Today sees the publication of the most recent addition to the series on fossil sirenians from the Western Atlantic and Caribbean (WAC) region (Velez-Juarbe and Domning, 2015). In our new paper we describe another new taxon from Puerto Rico (in July 2014 we described Priscosiren atlantica Velez-Juarbe and Domning, 2014). The material we describe in this new paper includes cranial and postcranial material from several individuals (Figures 1-5) and collected from several adjacent localities of the late Oligocene Lares Limestone in northwestern Puerto Rico*. We dubbed this new taxon Callistosiren boriquensis which translates into "Boriquen's most beautiful sirenian". Boriquén is the aboriginal name for the island of Puerto Rico, and "most beautiful" is in reference to the superb preservation of the type material (Figure 4).
*I've actually written and shown images of this fossil previously on this blog (here, here, here and here).
Figure 1. Callistosiren boriquensis is known from multiple elements of about five individuals (each color represents elements known from one or more specimens; white = unknown). Outline of skeleton modified from Cope (1890).
(Click on the image to see larger version.)The material we described in our paper includes two skulls, which actually account for the first and second sirenian skulls I found and collected, one in 2003, the other in 2005! The rest of the material we described which consists of ribs and vertebrae, was collected during an NSF-funded trip in 2009 with co-author Daryl Domning and with the help of my undergraduate advisor Hernán Santos and my colleagues Alvin Bonilla and Diana Ortega.
Figure 2. Left, me at the type locality during the first day (April 9, 2005) digging around the holotype skull (USNM 540765) (photo by MPT); top right, the skull (USNM 540765) during the second day (April 10, 2005) and ready to be jacketed; bottom right, early stages of preparation of the holotype skull (September 7, 2005).Figure 3. Top, some of the postcranial material referred to Callistosiren boriquensis prior to being collected, including the third lumbar (L3), sacral (S1) caudal (Ca1-4) vertebrae, and two chevrons (Ch). Below, my co-author Daryl Domning collecting other postcranial elements at type locality. Collected in June 2009.What is Callistosiren?
Callistosiren is a dugongine, which is the name given to the group of seacows that are more closely related to the dugong (Dugong dugon) of the Indopacific region than to Steller's seacow (Hydrodamalis gigas) and manatees. In fact, dugongines seemed to have originated and diversified in the Western Atlantic and Caribbean region and the group was present there until the mid to late Pliocene (Domning, 2001). Although one of the oldest dugongines, Callistosiren has morphological features that groups it amongst more derived members of the group. One of these features is that the enlarged tusks (I1 in Figure 4) of Callistosiren had enamel is confined to the medial (inner) surface, while the outside consist only of dentine. The result of this is that the lower edge of the tusks would wear off unevenly, forming a self-sharpening edge. This is something we also see in other dugongines such as some Dioplotherium and would presumably have been advantageous when cutting and uprooting seagrasses.

Figure 4. Dorsal, ventral and right lateral views of skull of Callistosiren boriquensis (modified from Velez-Juarbe and Domning, 2015:figs.1-3).Figure 5. Comparison between vertebrae (top) and ribs (bottom) of Callistosiren boriquensis (left) and Priscosiren atlantica (right). (Click on image to see larger version.) 
A lightweight among sirenians
When I first encountered the ribs and vertebrae of Callistosiren I was surprised by how skinny they were relative to those of other similarly sized sirenians such as Priscosiren (Figure 5). You see, sirenian bones are usually pachyosteosclerotic which means that they are dense and thickened (Domning and Buffénil, 1991). This is an adaptation that evolved very early in the evolutionary history of the group, with pachyostosis (thickened) and lightly osteosclerotic (dense) bones already present in one of the oldest sirenians, the middle Eocene Pezosiren portelli, and apparently becoming fully pachyosteosclerotic by the late Eocene (Buffrénil et al., 2010). This adaptation helps sirenians achieve neutral buoyancy and move in the water column with minimal effort, functioning in a similar fashion as a divers weight belt. There are few exceptions where sirenian bones deviate from this condition. One of these are the protosirenids, an extinct group of early sirenians, Callistosiren and extant dugong. One possible explanation for the lack of pachyostosis in dugong is that this species occasionally dives to depths greater than 10 meters, which is around when lungs begin to collapse, thus reducing buoyancy (Domning and Buffrénil, 1991). This may have been the case in Callistosiren, whose vertebrae and ribs are osteosclerotic, but not pachyostotic. Interestingly, Domning (2001) predicted the discovery of Caribbean sirenians with reduced ballast as another strategy for niche partitioning in sirenian multispecies communities and has now become true with the discovery of Callistosiren.


References

Buffrénil, V. de, A. Canoville, R. D'Anastasio, and D. P. Domning. 2010. Evolution of sirenian pachyosteosclerosis, a model-case for the study of bone structure in aquatic tetrapods. Journal of Mammalian Evolution 17:101-120.

Cope, E. D. 1890. The extinct Sirenia. American Naturalist 24:697-702.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 166:27-50.

Domning, D. P. and V. de Buffrénil. 1991. Hydrostasis in the Sirenia: quantitative data and functional interpretations. Marine Mammal Science 7:331-368.

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean region. XI. Priscosiren atlantica, gen. et sp. nov. Journal of Vertebrate Paleontology 34:951-964.

Velez-Juarbe, J., and D. P. Domning. 2015. Fossil Sirenia of the West Atlantic and Caribbean region. XI. Callistosiren boriquensis, gen. et sp. nov. Journal of Vertebrate Paleontology e885034

La entrada de hoy es una especial. Primero tenemos el honor de tener aquí a mi colega Catalina Pimiento que nos hablará de su más reciente publicación sobre tiburones fósiles. Segundo, es la primera vez que hago un "guest blog post" y espero no sea el último!
Catalina tomando los datos de unas vértebras fósiles de tiburón que encontramos en la Formación Chagres, en la costa caribeña de Panamá.Catalina, de nacionalidad colombiana, es actualmente candidata doctoral en la Universidad de Florida en Gainesville y además está asociada al Smithsonian Tropical Research Institute en Panamá. Durante su maestría, y ahora doctorado ha estudiado tiburones fósiles, con énfasis en material de Panamá (Pimiento et al., 2013a,b), y en descifrar la vida y existencia del tiburón más grande que ha existido, el Carcharocles megalodon (Pimiento et al., 2010; Pimiento and Clements, 2014). Sin más preámbulo los dejo con Catalina.
El Megalodón se extinguió hace 2.6 millones añosLa semana pasada salió publicado en la revista de acceso libre PLoS ONE, mi mas reciente estudio sobre el Megalodón, el tiburón más grande que ha existido (descargue el artículo aquí gratis!). Éste trabajo fue el resultado de un proyecto colaborativo con Chris Clements -experto en métodos matemáticos que permiten calcular fechas de extinción- y es parte de un proyecto más amplio, donde pretendo reconstruir la extinción de este gigante.
¿Por qué estudiar la extinción del Megalodón? El Megalodón resulta ser una especie muy importante, ya que era un súper-depredador. Los súper-depredadores son aquellos animales que están en lo más alto de la cadena trófica, y que no tienen amenazas por parte de otros depredadores. Éstos animales entonces mantienen la estabilidad de los ecosistemas a medida que controlan las poblaciones de sus presas. Por lo tanto, su eliminación produce efectos en cascada (afectando todos los niveles tróficos) con efectos catastróficos.
Dada su importancia, la extinción de los súper-predadores ha sido ampliamente estudiada por la ecología moderna. Estos estudios, sin embargo, han sido realizados en escalas temporales y geográficas muy limitadas y por lo general, con base en especies pequeñas. Asimismo, lo que se sabe sobre las extinciones de los súper-depredadores está basado en declives poblaciones o extirpaciones locales. El estudio de la extinción del Megalodón tiene entonces el potencial de ofrecer una perspectiva más amplia, no solo porque es una especie gigante y cosmopolita, sino porque tiene un amplio registro fósil que abarca millones de años.Algunos ejemplares de dientes de Megalodón, en este caso todos provenientes de Panamá. (Tomado de Pimiento et al., 2010.)Es por esto que la extinción del Megalodón ocupa desde hace ya algunos años la mayor parte de mi tiempo. Pero para lograrlo, el primer paso es saber cuándo sucedió. La extinción de las especies es algo que no podemos observar directamente. Aunque muchos científicos usan la fecha del fósil más reciente como una medida de la fecha de extinción, lo cierto es que las especies se extinguen tiempo después de la última vez que fueron registradas. Para calcular la fecha más probable de extinción, varios métodos basados en los últimos registros de las especies han sido desarrollados.
Los beneficios de las conferencias científicasEl año pasado, tuve el privilegio de asistir a una conferencia de Ecología (INTECOL) en Londres. Allí asistí a una charla sobre un trabajo experimental que probaba la eficacia de uno de los métodos que se han propuesto para calcular fechas de extinción. Me pareció paradójico que una charla donde se hablaba de protistas me resultara tan interesante, y decidí invitar al expositor (Chris Clements) a la charla que yo daría al día siguiente. En mi charla, hablé sobre mis estudios de la evolución del tamaño corporal del Megalodón, y de mis intenciones de hacer un meta-análisis de su registro fósil con el fin de reconstruir la extinción. Chris y yo nos reunimos más tarde ese día y decidimos estudiar la fecha de extinción del Megalodón, combinando los métodos con los que el trabaja, y mis ideas y resultados del meta-análisis.
El estudioEmpezamos por reunir los registros más recientes de la especie. Para eso, usamos como plataforma la Base de Datos de Paleobiología (PaleoBioDB). Como esta base de datos estaba incompleta (para Megalodón), colectamos todos los artículos que reportan la especie, y los adherirlos a la PaleoBioDB. Todos estos datos están accesibles al público.
Una vez construido el archivo de datos (#20 en la PaleoBioDB), evaluamos cada uno para asegurarnos de incluir en el análisis sólo aquellos que reportaban suficiente evidencia sobre la edad de los fósiles. Con este sub-grupo de datos, usamos el modelo de estimación linear óptima (OLE), el cual ha sido usado antes para calcular la fecha de extinción del Dodo. Este método calcula la fecha de extinción con base en la distribución de los registros más recientes. Como en nuestro caso, los registros no tienen una fecha absoluta, sino un rango de tiempo, re-muestreamos la edad de cada registro 10000 veces, desde su valor más alto, al mas bajo.
Los resultados sugieren que el Megalodón se extinguió hace 2.6 millones de años. Ya que se ha sugerido esta especie interactuaba con distintos grupos de ballenas, procedimos a contrastar los resultados con los patrones que se conocen de la evolución y diversificación de cetáceos.

Gráfica de distribución temporal de las fechas de extinción del Megalodón utilizando el modelo de estimación linear óptima. El área naranja representa la distribución de las fechas de extinción a través del tiempo, note que el pico está en el límite entre los periodos Plioceno y Pleistoceno. Las Barras horizontales en azul representan el rango de tiempo de los fósiles que fueron utilizados en el estudio, mientras que las barras grises fueron registros de fósiles cuyas edades no pudieron ser corroboradas y por ende no se utilizaron en el estudio. (Tomado de Pimiento and Clements, 2014.)¡Oh, sorpresa!La fecha de extinción del Megalodón, coincide con el límite entre los periodos Plioceno y Pleistoceno. Durante el Pleistoceno, las ballenas barbadas alcanzaron sus tamaños modernos gigantes. Por lo tanto, en nuestro estudio proponemos que el tamaño, y por ende, la función ecológica de las ballenas modernas, se estableció una vez se extinguió el tiburón más grande del mundo, el Megalodón.

Por ahora nuestro estudio solo proporciona la fecha de tan importante evento, y reconoce la coincidencia con la evolución del gigantismo en las ballenas modernas. Saber si un evento causó el otro, es nuestro siguiente paso.

ReferenciasPimiento, C., and C. F. Clements. 2014. When did Carcharocles megalodon become extinct? A new analysis of the fossil record. PLoS ONE 9(10):e111086.
Pimiento, C., D. J. Ehret, B. J. MacFadden, and G. Hubbell. 2010. Ancient nursery area for the extinct giant shark Megalodon from the Miocene of Panama. PLoS ONE 5:e10552.
Pimiento, C., G. González-Barbam D. J. Ehret, A. J. W. Hendy, B. J. MacFadden, and C. Jaramillo. 2013a. Sharks and rays (Chondrichthyes, Elasmobranchii) from the late Miocene Gatun Formation of Panama. Journal of Paleontology 87:755-774.
Pimiento, C., G. González-Barba, A. J. W. Hendy, C. Jaramillo, B. J. MacFadden, C. Montes, S. C. Suarez, and M. Shippritt. 2013. Early Miocene chondrichthyans from the Culebra Formation, Panama: a window into marine vertebrate faunas before the closure of the Central American Seaway. Journal of South American Earth Sciences 42:159-170.

Yes, fossil plants! This is a first in this blog, which is otherwise, heavily biased towards marine tetrapods. However, that doesn't mean that when I do fieldwork I only focus on collecting fossil vertebrates. this of course has resulted in a number of publication on fossil invertebrates (e.g. Schweitzer et al., 2006), and now plants. The paper which was just published in the journal International Journal of Plant Sciences is a collaborative work led by former Florida Museum of Natural History colleague Fabiany Herrera, one of the few experts on fossil plants from the Neotropics, and his former advisors Steven R. Manchester and Carlos Jaramillo. The paper is a follows up on a previous paper published about four years ago in the same journal (Herrera et al., 2010), and that seeks to better understand the evolutionary and paleobiogeographic history of a group of plants called Humiriaceae that are found in the Neotropics, and western Africa. This group is mainly composed of large trees, most greater than 20 meters tall, and fruits have woody parts with very particular morphology, which results in a relatively high preservation and identification potential.
Map showing the distribution of fossil Humiriaceae endocarps (symbols) and extant genera (dashed lines) (modified from Herrera et al., 2010:fig. 1).In the paper we describe fossilized endocarps (the inside part of the fruit) from the early Oligocene of Peru and Puerto Rico, and the late Miocene of Panama, and fossilized wood from the late Eocene of Panama (Herrera et al., 2014). The fossilized fruit from the Oligocene of Peru, which we dubbed Duckesia berryi, represents a new species of a tree that is nowadays only found in Amazonia, and is the oldest record of that genus. This not only shows that this particular taxon has an older history than previously thought, but it also shows that its former distribution was much more widespread. In addition to that, the fossil wood we describe, called Humiriaceoxylon ocuensis, shows that by the late Eocene parts of what is now Panama, was forested by large trees belonging to this particular group of plants. In addition, Fabiany had previously described a fossil Humiriaceae endocarp which he names Lacunofructus cuatrecasana from a locality near where the wood was found, and it may actually be that they represent the same tree (Herrera et al., 2012, 2014)*. This is a really cool find, as the region and where the fossils were collected, was not connected by land to neither North or South America, showing again, that overwater dispersal is not as much a problem for plants.
*Paleobotanists use different scientific names for the different parts of a plant as they are usually found separate, hence the endocarp has a name, and the wood another, even though they may be the same plant.
The fossil endocarp Duckesia berry (A-L) from the Oligocene of Peru, compared with the endocarp of the modern species D. verrucosa (M-O). (Modified from Herrara et al., 2014:fig. 1.)The fossil from Puerto Rico consists of an endocarp of Sacoglottis tertiaria, otherwise known from the Neogene of Peru, Ecuador, Colombia and Panama (Herrera et al., 2010). Several species of the genus Sacoglottis are still found today, in the Amazonian region and west Africa. The fossil from Puerto Rico is from the early Oligocene San Sebastian Formation, one of my favorite formations where I've spent many hours searching for fossils. Actually, the locality where I found the endocarp is not far from where Aktiogavialis puertoricensis, Priscosiren atlantica, and a Caviomorph rodent tooth were collected (Velez-Juarbe et al., 2007; Velez-Juarbe and Domning, 2014; Velez-Juarbe et al., 2014).
The fossil endocarp Sacoglottis tertiaria from the early Oligocene San Sebastian Formation of Puerto Rico.Fossil plants were previously described from the San Sebastian Fm. by previous workers, mainly, Arthur Hollick (1928) and Alan Graham and David Jarzen (1969). But none of the material they described indicated the presence of Humiriaceae in the island. In fact, they list many plant groups present in San Sebastian Fm. which are now absent from the flora of the island, now the Humiriaceae can be added to that list. As I recently said in a newspaper interview, Puerto Rico during the Oligocene was very different from nowadays, and there is still more to be discovered!

Assorted Musing
The fossil endocarp from Puerto Rico, was previously featured on this blog, it was the only thing I found in my two days of fieldwork in January 2009. I was a bit disappointed at first, but not any more!

I should also acknowledge my wife, it was because of her that I ended up visiting the Florida Museum of Natural History in the fall of 2012, which is where I met Fabiany, told him about the fossil endocarp, and I ended up being a co-author in his paper.

References

Graham, A., and D. M. Jarzen. 1969. Studies in Neotropical paleobotany. I. The Oligocene communities of Puerto Rico. Annals of the Missouri Botanical Garden 56:308-357.

Herrera, F., S. R. Manchester, and C. Jaramillo. 2012. Permineralized fruits from the late Eocene of Panama give clues of the composition of forests established early in the uplift of Central America.

Herrera, F., S. R. Manchester, J. Velez-Juarbe, and C. Jaramillo. 2014. Phytogeographic history of the Humiriaceae (Part 2). International Journal of Plant Sciences 175:828-840.

Herrera, F., S. R. Manchester, C. Jaramillo, B. MacFaddem, S. A. da Silva-Caminha. 2010. Phytogeographic history and phylogeny of the Humiriaceae. International Journal of Plant Sciences 171:392-408.

Hollick, A. 1928. Paleobotany of Porto Rico. Scientific Survey of Porto Rico and the Virgin Islands 7(3):177-393.

Schweitzer, C. E., M. Iturralde-Vinent, J. L. Hetler, and J. Velez-Juarbe. 2006. Oligocene and Miocene decapods (Thalassinidea and Brachyura) from the Caribbean. Annals of Carnegie Museum 75:111-136.

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean region: X. Priscosiren atlantica, gen. et sp. nov. Journal of Vertebrate Paleontology 34:951-964.

Velez-Juarbe, J., C. A. Brochu, and H. Santos. 2007. A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile. Proceedings of the Royal Society B 274:1245-1254.

Velez-Juarbe, J. T. Martin, R. D. E. MacPhee, and D. Ortega-Ariza. 2014. The earliest Caribbean rodents: Oligocene caviomorphs from Puerto Rico. Journal of Vertebrate Paleontology 34:157-163.

Today came out the most recent issue of the Journal of Vertebrate Paleontology. Amongst many other interesting papers, there is one by yours truly and former PhD advisor Daryl Domning. In our paper we describe a new sirenian taxon from early Oligocene deposits in Puerto Rico and South Carolina, its our second new species this year, as some months ago we published the description of Metaxytherium albifontanum Velez-Juarbe and Domning, 2014 (read more about it here). The fossil from Puerto Rico, which is fairly complete, comes from the same overall locality as some other fossils I've mentioned in previous posts, like Aktiogavialis puertoricensis Velez-Juarbe et al., 2007, and the oldest West Indian rodent (Velez-Juarbe et al., 2014).  This paper also marks the Tenth (!!!!) installment of the series on Fossil Sirenia of the West Atlantic and Caribbean Region, which Daryl started in 1988 (Domning, 1988)! Such long-lasting series are very uncommon!

The last time a new species of sirenian was described from Puerto Rico was 1959, when Roy H. Reinhart in his monumental work on Sirenia and Desmostylia, described Caribosiren turneri (see picture below) from the San Sebastian Formation in the northwestern part of the island. Caribosiren is a weird dugongid, it has a rostral deflection (downturning of the snout) of nearly 90º, and apparently no tusks!!
Caribosiren turneri Reinhart, 1959, from the San Sebastian Formation of Puerto Rico. Notice the extremely downturned snout  which always reminds me of Gonzo! The tip of the snout, although not preserved very well, hints at a lack of tusks.
(Photo courtesy of N.D. Pyenson) (Click on image to see larger version.)The new fossil is from the same formation as Caribosiren. We named our new species Priscosiren atlantica, in reference to its ancestral relationship to other fossil dugongids (prisco means ancient, former) and its occurrence in the Western Atlantic region.
Priscosiren atlantica is known from multiple elements of two individuals, one from the Puerto Rico (USNM 542417) the other from South Carolina (SC 89.254). Its one of the most complete early Oligocene sirenians known. (Outline of skeleton modified from Cope, 1890).
(Click on image to see larger version.)
Slides from a talk that Daryl and I gave at the 2013 SVP annual meeting. Here we point out to several of the characters that diagnose Priscosiren atlantica as well as its relationship to other dugongids.
(Click on image to see larger version.) Priscosiren is represented by at least two individuals (an adult and a subadult), with associated cranial and postcranial material, making it one of the best known early Oligocene sirenians. This species occupies a special place amongst other dugongids as it seems to be ancestral (hence its name) to a clade that includes Metaxytherium spp. + Hydrodamalinae, and Dugonginae (see above). More interestingly, is that Priscosiren is found in the same formation as Caribosiren in Puerto Rico, and Crenatosiren olseni in South Carolina, and hints at the presence of sirenian multispecies communities (Velez-Juarbe et al., 2012) during the early Oligocene.

The day we found the holotype specimen of Priscosiren (USNM 542417) was the same day we found the holotype of Aktiogavialis puertoricensis, which we were able to collect that same day. In contrast, collecting Priscosiren was an ordeal, it is a long story, of discovery, failed attempts at collecting it, loss of parts, and final recovery. So stay tuned for an upcoming post about that story!

References

Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean Region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:395-426.

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.

Velez-Juarbe, J., C. A. Brochu, and H. Santos. 2007. A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a nonmarine reptile. Proceedings of the Royal Society B 274:1245-1254.

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean Region. IX. Metaxytherium albifontanum. Journal of Vertebrate Paleontology 34:444-464.

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean Region. X. Priscosiren atlantica gen. et sp. nov. Journal of Vertebrate Paleontology 34:951-964.

Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7:e31294.

Velez-Juarbe, J., T. Martin, R. D. E. MacPhee, and D. Ortega-Ariza. 2014. The earliest Caribbean rodents: Oligocene caviomorphs from Puerto Rico. Journal of Vertebrate Paleontology 34:157-163.

Dear readers, things have been a bit quiet here, mostly because lots of exciting things have been happening! To begin, earlier this year Caribbean Paleobiology moved to the West Coast, after spending most of the last 6 and a half years between Washington DC, Florida and Panama. The reason for the move is that I am now an NSF Postdoctoral Fellow based with Jim Parham and at the John D. Cooper Archaeological and Paleontological Center, Department of Geological Sciences, California State University-Fullerton, and also, starting next month, I'll be the new curator of Marine Mammals (living and extinct) at the Natural History Museum of Los Angeles County!!
My postdoc project will be sort of a follow-up on a paper I published on sirenian multispecies assemblages a couple of years ago, now it will be taxonomically broader and focused on a different part of the world. By taxonomically broader I mean sirenians, desmostylians and aquatic sloths! All which were, or are considered, marine mammal herbivores.

Since arriving in California I've been busy visiting some sites like Sharktooth Hill, and museum collections, including the San Diego Natural History Museum, the museum at the Universidad Autónoma de Baja California, in Ensenada, and a return trip to Washington DC to attend the 2014 Secondary Adaptations meeting and of course the collections at the National Museum of Natural History in DC.
Sharktooth Hill National Natural Landmark in Bakersfield, California. The famous bone bed is about 10 meters or so below the car.Tania (my wife) hold the first neck vertebra of Hydrodamalis cuestae, which was the largest species of sea cow, ever! It reached more than 8 meters in length, large for a sea cow, but small when compared to some whales.One of the highlights of the 2014 SecAd meeting. We got a brief lecture on beaked whales from Jim Mead curator emeritus of marine mammals at the Smithsonian and one of the Worlds expert on that group of whales.
The other thing that's has kept me busy is that back in May, I was in Baja California Sur with several colleagues from Howard University (HU), New York Institute of Technology (NYIT), Universidad Autónoma de Baja California (UABC), and Universidad Autónoma de Baja California Sur (UABCS), most which you can see in the picture below. This trip was a continuation of work we did back in 2012 (see previous post about that trip). The trip was fun, and we found many interesting fossils.
Part of the BCS Paleo Project 2014 reopening the main quarry. From left to right, Arely Cedillo (UABCS), Gerardo González (UABCS), Ehecatl Hernández (UABCS), Brian Beatty (NYIT), Daryl Domning (HU), and Lizeth González (UABCS). Missing from the picture Azucena Solis (UABCS) and Fernando Salinas (UABC). Click on the picture to see the larger version.So, stay tune as new papers will be coming out soon and I'll get around to post some more about the Baja trip!!

Yesterday saw the publication (online) of the second issue of 2014 of Journal of Vertebrate Paleontology. Published in this issue is the description of the first new species of seacow from the Western Atlantic that I get to name. In collaboration with Daryl P. Domning, this is the latest installment in the series titled "Fossil Sirenia of the West Atlantic and Caribbean Region" which Daryl started in 1988 (Domning, 1988). Our new species, named Metaxytherium albifontanum is known from late Oligocene deposits in Florida and South Carolina. The generic name albifontanum translates into white springs (albus = white; fontanus = spring or fountain). But why did we choose that name? and what is Metaxytherium? Keep reading and you'll find out why and more. 
Scientific Names
The scientific name of organisms consist of two parts: the genus and the species. The genus is a more inclusive rank, whereas the species is more unique. In a way, you can think of the genus name as an equivalent to your last name, where there will be more members (e.g. siblings and/or parents) with that same last name, and the species name as your first name; the two, together, will form a unique combination which applies only to you. We use scientific names in order to infer relationships amongst organisms, and these are usually latinized so that they can be understood by anyone, anywhere, as a common language, instead of using the common name which changes by country and language. Now, when describing a new species and giving it a scientific name, you can choose whichever name you think appropriate, as long as its not your own (Linnaeus was the one exception; there are other rules for naming, which you can find here). You can name a species after a musician who was an inspiration, the country where it was found, or in honor of a fellow researcher, just to name a few examples.
Renowned paleontologist George Gaylord Simpson named several fossil sirenians from Florida (Simpson, 1932). Simpson had a thing for using cleverly latinized versions of formation or locality names for his new species. For example, he described some fossils from the Bone Valley district in central Florida and gave them the scientific name Felsinotherium ossivallense*, (ossivallense = Bone Valley), while another one he named Hesperosiren crataegensis*, which takes its name from Crataegus, the genus name of a plant commonly known as hawthorn, which in turn is also the name of the sedimentary unit, the Hawthorn Group, where Simpson's specimen was found. So, as a homage to G. G. Simpson and his work on the fossil sirenians from Florida we decided to use a latinized version of the name of the town of White Springs, FL, which is close to where the holotype (= name-bearing specimen) of our new species was collected; resulting in the combination Metaxytherium albifontanum.
*both Felsinotherium and Hesperosiren were later synonymized with Metaxytherium


Metaxytherium albifontanum is known from multiple elements of several individuals (each color identifies elements represented by one or more specimens; white = unknown). This makes it one of the most complete fossil sirenians known. (Outline of skeleton modified from Cope, 1890). (Click on the image to see larger version.)What is Metaxytherium
Metaxytherium is a widespread and relatively well-known genus of fossil dugongid. There are now a total of eight species under this genus, it has a wide temporal distribution, ranging from the late Oligocene through early Pliocene, and a broad geographical distribution, with species known from Europe, northern Africa, and the Americas. Most of the species known were described and named between 1822 and the first half of the 1900's, so, unexpectedly, there was a bit of a taxonomic mess (this happens more often than we'd like). Fortunately, since 1987, there have been several papers providing us with detailed descriptions of some of the known species, as well as phylogenetic analyses (e.g. Domning and Thomas, 1987; Domning, 1988; Aranda-Manteca et al., 1994; Domning and Pervesler, 2001; Sorbi, 2008; Sorbi et al., 2012). These works have help clarify some of the taxonomic confusion surrounding some of the old names, and even a new species was described, Metaxyterium arctodites Aranda-Manteca et al., 1994, from Baja California and California. That makes M. albifontanum the first species of Metaxytherium named in 20 years!! Meaning that we are not done learning about the diversity of this group, and more may still be waiting to be described.


Slides from a talk Daryl and I gave at the Society of Vertebrate Paleontology 2013 Annual Meeting. Here we use M. albifontanum to illustrate some of the features that characterize the genus Metaxytherium (top two and bottom left). The phylogenetic tree on the bottom right shows the relationship between Metaxytherium spp. and other sirenians (modified from figure 15 of our paper). (Click on the image to see larger version.) Our new species differed from all other known species in the group. Not only that, it is the geologically oldest species of Metaxytherium. Previous assumptions on the origins of Metaxytherium had hypothesized an European origin for the group, our discovery changes that and seems to indicate a Western Atlantic origin for the genus.

Relationships with Other SpeciesOne of the relevant results of our paper is that we got to properly define Metaxytherium. Our phylogenetic analysis (see tree above, bottom right) was consistent with previous work (e.g. Domning, 1994), showing a close relationship between Metaxytherium spp. and hydrodamalines (the group that include Steller's seacow). We also got some interesting results regarding the relationships amongst the different species of Metaxytherium. Our results indicate that the split between Metaxytherium albifontanum and the geologically younger M. krahuletzi (from the early Miocene of Europe), occurred before the late Oligocene, as the latter occupies a more basal position within the tree. The relationships within the group also seem to point to multiple dispersals across the Atlantic and/or a high degree in morphological convergence.
PaleoecologyMetaxytherium albifontanum was part of a sirenian multi-species assemblage in the late Oligocene of Florida, together with Dioplotherium manigaulti and Crenatosiren olseni. As part of that assemblage, we hypothesize M. albifontanum as a consumer of small-sized seagrasses such as eelgrass, while the other species likely fed on larger species. If this sounds familiar is because I wrote about this subject in a previous post. In fact, M. albifontanum was one of the species that inspired the iterative evolution project with Daryl and Nick Pyenson, which resulted in our open access publication in PLoS ONE (Velez-Juarbe et al., 2012). 
Assorted Random Musing: 

• I visited the Florida Museum of Natural History in 2011 to study one of the specimens (UF 49051), little did I know at that time that I would end up as a Postdoc here!
• You can see the name-bearing specimen, UF 49051, in the Florida Fossils: Evolution of Life and Land exhibit at the Florida Museum of Natural History.
• It so happened that I wrote this post from a desk at the Simpson Library of Paleontology, its filled with books and reprints donated by him, and...
• There are a lot of pictures of Simpson in this library, in some, he kind of looks like the long lost brother of Colonel Sanders...

Stay tuned as more new fossils seacows will be showing up here later this year!!

References
Aranda-Manteca, F. J., D. P. Domning, and L. G. Barnes. 1994. A new Middle Miocene sirenian of the genus Metaxytherium from Baja California: relationships and paleobiogeographic implications. Proceedings of the San Diego Society of Natural History 29:191-204.
Cope, E. D. 1890. The extinct Sirenia. American Naturalist 24:697-702.
Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean Region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:395-426.
Domning, D. P. 1994. A phylogenetic analysis of the Sirenia. Proceedings of the San Diego Society of Natural History 29:177-189.

Domning, D. P., and P. Pervesler. 2001. The osteology and relationships of Metaxytherium krahuletzi Depéret, 1895 (Mammalia: Sirenia). Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft 553:1-89.
Domning, D. P., and H. Thomas. 1987. Metaxytherium serressii (Mammalia: Sirenia) from the early Pliocene of Libya and France: a reevaluation of its morphology, phyletic position, and biostratigraphic and paleoecological significance; pp. 205-232 in N. Boaz, A. El-Arnauti, A. W. Gaziry, J. de Heinzelin, and D. D. Boaz (eds.), Neogene Paleontology and Geology of Sahabi. New York (Liss).
Simpson, G. G. 1932. Fossil Sirenia of Florida and the evolution of the Sirenia. Bulletin of the American Museum of Natural History 59:419-503.
Sorbi, S. 2008. New record of Metaxytherium (Mammalia, Sirenia) form the lower Miocene of Manosque (Provence, France). Geodiversitas 30:433-444.
Sorbi, S., D. P. Domning, S. C. Vaiani, and G. Bianucci. 2012. Metaxytherium subapenninum (Bruno, 1839) (Mammalia, Dugongidae), the latest sirenian of the Mediterranean Basin. Journal of Vertebrate Paleontology 32:686-707.
Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean Region. IX. Metaxytherium albifontanum sp. nov. Journal of Vertebrate Paleontology 34:444-464.
Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7:e31294.

Hoy sale publicado en la revista científica Proceedings of the Royal Society B el trabajo titulado Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea (lo pueden bajar GRATIS). El mismo, es el resultado de un proyecto colaborativo entre investigadores nacionales e internacionales y donde se combina el uso de herramientas tradicionales de la paleontología con equipos y técnicas innovadoras para obtener datos tales como digitalización 3D y fotogrametría. En este trabajo tomamos un enfoque multidisciplinario para descubrir que le ocurrió a un grupo de vertebrados marinos que murieron al mismo tiempo y posteriormente fueron depositados y preservados en lo que fuese una planicie de marea en la costa del norte de Chile a finales del periodo Mioceno (entre 6-9 millones de años atrás). La localidad donde se hizo el estudio se le conoce como Cerro Ballena, la cual está localizada en la Región de Atacama (cerca del desierto más seco del mundo), y al norte del pueblo de Caldera (lugar que inspiró al autor de Condorito y donde se venden las mejores empanadas que he comido).
Vista desde el extremo sur de Cerro Ballena, desde aquí se puede observar el pueblo de Caldera y océano Pacífico. La Carretera que se ve es parte de la Autopista Panamericana.Gracias a las fuerzas tectónicas que a través del tiempo han cambiado la costa occidental de América del Sur, Cerro Ballena se encuentra hoy día alejado de la costa y sobre el nivel del mar. Si "Cerro Ballena, Chile y cetáceos fósiles" les suena familiar en este blog, es porque hace casi dos años atrás fui parte de una expedición científica donde recolectamos datos para este trabajo (visiten las entradas anteriores sobre ese viaje aquí, aquí, aquí, aquí, y aquí).

El Descubrimiento
Previo a nuestro trabajo, ya se conocía sobre la existencia de fósiles en Cerro Ballena, por ende el nombre. Sin embargo, los fósiles que se encontraban allí no estaban completamente expuestos, por lo cual colectarlos para estudiarlos hubiera sido muy laborioso y costoso. Afortunadamente, durante los trabajos de ensanchamiento de la Autopista Panamericana, la cual pasa por la localidad, muchos de estos fósiles quedaron expuestos y se notó que estos sólo se encontraban en ciertas capas sedimentarias, todas pertenecientes a una formación geológica llamada Formación Bahía Inglesa. Al ser tan grande la cantidad de fósiles que quedaron expuestos tuvieron que detener el trabajo de ensanchamiento de la autopista para rescatar los mismos. Estos esfuerzos fueron liderados por un equipo de paleontólogos del Museo Paleontológico de Caldera, el Museo Nacional de Historia Natural de Chile y la Universidad de Chile, los cuales se encargaron de mapear la posición de cada fósil en su respectivo horizonte. Más tarde se unieron a ese esfuerzo los integrantes de la oficina de digitación 3D del Smithsonian quienes hicieron scans de los fósiles in situ para poder salvaguardar esa información ya que pasará mucho tiempo para que algunos de estos sean preparados y estudiados en detalle.

Algunas de las ballenas siendo preparadas para ser colectadas. Cada carpa negra indica la localización de una ballena. A la derecha Ana M. Valenzuela-Toro, una de las coautoras del trabajo junto al espécimen B33.El equipo de digitación 3D del Smithsonian. Adam Metallo (izquierda) y Vincent Rossi (derecha) utilizan varias herramientas para escanear a la ballena B33. Gracias al scan se pueden hacer imágenes como la que utilicé arriba para el banner de este blog al igual que imprimir copias 3D del mismo.Aquí las ballenas ya colectadas y guardadas en el Museo Paleontológico de Caldera. No es inusual encontrar fósiles de vertebrados marinos en esta parte del mundo, de hecho, más al norte en Perú se encuentra la Formación Pisco, la cual es similar en edad a la Formación Bahía Inglesa (ronda entre los 10-4 millones de edad) y es una de las formaciones geológicas más estudiadas y más conocidas por su diversidad de mamíferos marinos extintos. Sin embargo, Cerro Ballena es diferente a lo que se ha encontrado en la Pisco y estas diferencias son lo que hacen Cerro Ballena un lugar especial.

Miembros del Team Ballena tomando datos de los horizontes fosilíferos en Cerro Ballena.El Misterio de Cerro Ballena
En Cerro Ballena logramos identificar cuatro horizontes fosilíferos. Cada horizonte contenía un conjunto de vertebrados marinos, siendo la atracción principal la presencia de esqueletos completos o casi completos de ballenas barbadas, algunas hasta de 8 metros (26 pies) de largo. Nuestras observaciones indicaban que lo que pasó en Cerro Ballena fueron varios eventos de varamiento masivo. Quizás ya hayan escuchado sobre varamiento masivos de mamíferos marinos, ya que es un fenómeno que generalmente capta la atención de lo medios noticiosos. De hecho, muchos de los los varamientos masivos que ocurren hoy día generalmente incluyen a los cetáceos dentados (odontocetos: delfines, marsopas, cachalotes, etc). Un causante principal de este tipo de varamiento resulta como efecto secundario del uso de sonar por las marinas de guerra. Sin embargo los eventos que ocurrieron en Cerro Ballena tomaron lugar millones de años atrás, cuando nuestros ancestros eran muy primitivos y ni siquiera habían salido de África, así que podemos descartar esa causa para lo que ocurrió allí. Lo peculiar de Cerro Ballena, es que junto con las ballenas barbadas también encontramos otros vertebrados marinos, incluyendo cachalotes, delfín-morsa, focas, perezosos acuáticos y marlines. Esta ocurrencia multi-taxonómica señala a algún otro tipo de mecanismo que afectó por igual a todos estos vertebrados marinos y causó su varamiento masivo. Afortunadamente (bueno, quizás no para los animales) varamientos masivos que incluyen distintos grupos de vertebrados marinos ocurren hoy día. Estudios detallados de este tipo de varamientos han determinado que los mismos ocurren por intoxicación causada por floración de algas nocivas (también conocidos como marea roja). Las mareas rojas son comunes en zonas de surgencia, y gracias a estudios previos, sabemos que la costas de Chile y Perú son zonas de surgencia desde hace millones de años. Esta peculiar localidad no solo nos permite una ventana al pasado y descubrir un ecosistema marino con organismos distintos a los que vemos hoy día, si no que también nos permitió descubrir que eventos de marea roja, muy similares a los que todavía observamos hoy día y que continúan afectando a los vertebrados marinos han estado ocurriendo durante millones de años. Incluso, podemos predecir que otros depósitos fosilíferos ricos en vertebrados marinos en zonas de turgencia, como por ejemplo la Formación Pisco en Perú, puede que hayan preservado eventos como los que descubrimos en Cerro Ballena.
Nuestro trabajo en Cerro Ballena aún no termina, todavía nos queda describir en detalle muchos de los organismos que vivieron, y murieron en la costa chilena hace millones de años atrás.

Para mayor información sobre nuestro proyecto visiten la página oficial de Cerro Ballena.

En la página de Smithsonian X 3D pueden ver parte los fósiles que fueron escaneados e incluso si tienes acceso a una impresora 3D, imprimir tu copia personal de los fósiles.

También visiten la página del Pyenson Lab donde encontrarán más fotos y entradas sobre las distintas expediciones a Chile.

Visiten también:
Not Exactly Rocket Science
Smithsonian Science
Smithsonian Magazine
Science Magazine
PhysOrg
BBC News
Washington Post

Referencia:

Pyenson, N. D., C. S. Gutstein, J. F. Parham, J. P. Le Roux, C. Carreño Chavarría, H. Little, A. Metallo, V. Rossi, A. M. Valenzuela-Toro, J. Velez-Juarbe, C. M. Santelli, D. Rubilar Rogers, M. A. Cozzuol, and M. E. Suárez. 2014. Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea. Proceedings of the Royal Society B [in press].

Ya estamos en enero, el primer mes del nuevo año y con el llega la primera edición del año de la revista científica Journal of Vertebrate Paleontology. En este ejemplar se han publicado muchos trabajos interesantes, incluyendo varios sobre mamíferos marinos, lo cual es un tema recurrente en este blog. Sin embargo, en esta entrada hablaremos de otros fósiles. En esa misma edición ha salidos publicado un trabajo donde mis colegas y yo describimos fósiles de roedores de Puerto Rico (Vélez-Juarbe et al., 2014). Estos fósiles son únicos ya que son la evidencia más antigua de roedores caviomorfos en las Antillas Mayores, y nos ayudan a entender el cuando llegaron los vertebrados terrestres a la región, lo cual ha sido tema de debate durante varias décadas.

Roedores fósiles de Puerto Rico
No es la primera vez que se encuentran fósiles de roedores en Puerto Rico. De hecho, es bien conocido que durante el Pleistoceno* en Puerto Rico, La Española, Cuba, Jamaica, y algunas de las Antillas Menores, habitaban distintos grupos de roedores endémicos, perezosos terrestres, monos, y musarañas (Woods y Sergile, 2001). Muchos de estos fósiles de mamíferos terrestres del Pleistoceno fueron descritos a principios del siglo pasado (e.g. Anthony, 1918), aunque han habido descubrimientos más recientes (Turvey et al., 2006). Algunos de los roedores fósiles que han sido descritos de estas islas eran gigantes, como por ejemplo, Amblyrhiza inundata de la isla de Anguila, la cual tenía una masa corporal similar a la de un oso negro americano (Biknevicious et al., 1993)!
*periodo geológico que comenzó hace 2.6 millones de años y duró hasta hace 10,000 años

Siendo más específico, durante el Pleistoceno, en Puerto Rico habitaban al menos tres especies de ratas espinosas (Heteropsominae), y posiblemente dos especies de hutías gigantes (Heptaxodontidae) (información adicional aquí). Un tercer grupo de roedores endémicos que existió durante el mismo tiempo, en incluso todavía habita algunas de las otras Antillas, eran las hutías capromíidas, pero hasta donde sabemos estas nunca habitaron Puerto Rico. Todos estos grupos de roedores pertenecer a un grupo taxonómico más grande llamados caviomorfos. Los caviomorfos son endémicos de Sur América; sus ancestros llegaron de África alrededor de 54 millones de años atrás (Antoine et al., 2012). Una vez llegan a Sur América, los caviomorfos se diversifican y se dispersan a través de todo el continente y el Caribe. Algo muy similar también ocurrió con los primates suramericanos (platirrinos) (Kay, 2014), los cuales tienen una historia casi tan antigua como los roedores caviomorfos.
Foto tomada a principios de enero cuando visité de nuevo la localidad de las Calizas Lares donde encontré el diente incisor.Los nuevos fósiles de Puerto Rico consisten de un par de dientes incisores, uno proveniente de la Formación San Sebastián, y el otro de las Calizas Lares (ver foto arriba). Respectivamente, estas formaciones se depositaron durante las épocas geológicas conocidas como Oligoceno temprano (29.78-26.51 Ma) y Oligoceno tardío (26.51-24.73 Ma) (Ortega-Ariza et al., 2015). Cuando encontré los fósiles allá para el 2005, me comuniqué con Ross MacPhee, curador de mamíferos del Museo Americano de Historia Natural en Nueva York, y quien durante años ha tenido interés en los orígenes de la fauna terrestre de las Antillas Mayores. Basado en lo que ya conocíamos sobre el registro fósil de Puerto Rico, Ross y yo sospechábamos que estos dientes incisores pertenecían a un roedor caviomorfo. Sin embargo, teníamos un problema, como pueden observar en la foto abajo a la derecha, los incisores son muy sencillos, ya que carecen de las crestas, cúspides y valles que uno vería en un molar, esto nos hacía difícil el poder identificarlos usando solo sus características externas. Lo siguiente que se nos ocurrió fue tratar de ver la estructura microscópica (microestructura) del esmalte, esta si preserva características que nos podrían ayudar a identificar el diente y saber a que grupo de roedores pertenecía. Estudiar la estructura microscópica de los dientes toma varios pasos: hay que hacer un corte transversal del diente, pulir la superficie y finalmente, utilizando un microscopio electrónico de barrido, ver la microestructura del diente. Para llevar a cabo esta tarea decidimos contactar a Thomas Martin, paleontólogo de la Universidad de Bonn, en Alemania y quien es uno de los expertos en el estudio de microestructura de los dientes. Luego convencer a Thomas, le enviamos los fósiles, y luego de varios meses, nos envió un correo electrónico con detalles de los resultados.
A la izquierda una representación de como son los roedores caviomorfos mostrando la posición del diente incisor. A la derecha el diente incisor fósil de la Formación San Sebastián. Arriba, imagen de microscopio electrónico de barrido mostrando la estructura microscópicas del incisor (píquenle a la imagen para que la vean más grande).  El correo que nos envió Thomas fue muy alentador. Después de todo, resultó que nuestros fósiles si pertenecían a roedores caviomorfos, confirmando lo que ya sospechábamos. Ahora que sabíamos a que tipo de roedor pertenecían los dientes, y su importancia respecto a los orígenes de la fauna antillana, deseábamos obtener edades más precisas para las localidades. Para esto me comuniqué con mi amiga y colega Diana Ortega-Ariza, candidata doctoral de la Universidad de Kansas. Diana hizo su maestría en el Departamento de Geología en la Universidad de Puerto Rico (mi alma mater) donde estudió las distintas unidades calizas del norte de la isla, incluyendo las Calizas Lares. Como parte de su estudio ella obtuvo edades radiométricas utilizando isótopos de estroncio* preservados en los tubos calcíticos que servían de hogar a el bivalvo Kuphus incrassatus, el cual es uno de los fósiles más comunes en rocas del Oligoceno y Mioceno. Los resultados de ese estudio isotópico revelaron que las Calizas Lares se depositaron entre 26.51-24.73 millones de años atrás durante una era geológica llamada Chattiano la cual es la subdivisión más joven del Oligoceno**. Esa edad la podíamos entonces utilizar para estimar que la Formación San Sebastián, la cual se encuentra debajo de la Lares, tiene una edad mayor de 26.51 millones de años, en otras palabras, que esa formación se depositó durante el Rupeliano, la cual es la subdivisión más antigua del Oligoceno.
*Este tipo de análisis funciona de forma similar al Carbono 14, con la ventaja que nos sirve para fechar fósiles más viejos. Las edades máximas que se pueden obtener con Carbono 14 son de 50,000 años, mientras que el estroncio nos sirve para calcular fechas de hasta cientos de millones de años.
**Todo el periodo Oligoceno duró entre 33.9-23.0 millones de años atrás y tiene dos subdivisiones Chattiano y Rupeliano.

Orígenes de los vertebrados terrestres de las Antillas Mayores
Charles Darwin nunca estuvo en las Antillas. Aún así, la fauna de la región no pasó desapercibida y este incluso escribió en uno de sus libros más populares Voyage of the Beagle que "El caracter suramericano de los mamíferos antillanos parece indicar que este archipiélago estuvo en algún momento unido al continente sureño, y que subsiguientemente ha sido un área de subsistencia." Darwin, al igual que muchos otros antes y después de el, tenía razón respecto al lugar de origen de los mamíferos terrestres de las Antillas. Sin embargo, una de las preguntas más debatidas no ha sido el donde, sino el cuando llegaron los ancestros de los vertebrados terrestres de las Antillas.

Por años, el debate se ha centrado en dos hipótesis: una propone que estos llegaron a la región mediante múltiples eventos de dispersión a lo largo de los últimos 60 millones de años (e.g. Hedges et al., 1992), la otra, que llegaron alrededor del mismo tiempo durante un solo evento de dispersión (e.g. MacPhee e Iturralde-Vinent, 1995). La hipótesis de GAARlandia* propone que entre el Eoceno tardío y Oligoceno temprano las islas de Cuba, Española, y Puerto Rico junto con la Cresta de Aves formaron un puente terrestre casi continuo que los unió con el norte de Sur América (vean la figura abajo). Este puente terrestre, aunque de poca duración - probablemente estuvo formado entre 37.8-28.1 millones de años atrás - sirvió como un corredor para la dispersión de vertebrados terrestres hacia las masas terrestres que más tarde pasarían a ser las Antillas Mayores (para un resumen detallado de la evidencia geológica vean Iturralde-Vinent y MacPhee [1999]). Esto significa que, idealmente, deberíamos encontrar fósiles de mamíferos terrestres en depósitos del Eoceno tardío-Oligoceno temprano que representen a los mismos grupos que conocemos del Pleistoceno.
*Greater Antillean Aves Ridge land (MacPhee e Iturralde-Vinent, 1995)
Figura 1 de nuestra publicación. Aquí mostramos las distintas localidades (A) en Sur América donde se encuentran roedores fósiles del Eoceno y Oligoceno junto con la localidad de Domo de Zaza (DZ) en Cuba donde se han encontrado roedores del Mioceno temprano. En la figura B vemos las localidades de Puerto Rico, Río Guatemala (RG) y Calizas Lares (LL). C muestra la reconstrucción paleogeográfica de la región del Caribe durante el Eoceno tardío-Oligoceno temprano. Durante este periodo Cuba, La Española y Puerto Rico estaban unidos a la Cresta de Aves formando un puente terrestre conectando con el norte de Sur América.El registro fósil de la región no nos ha fallado y nos ha dado algunos fósiles que apoyan esta segunda hipótesis. Uno de los primero que se descubrieron fue parte de un fémur (hueso del muslo) de un perezoso terrestre (megaloniquido) en la Formación Juana Díaz, al suroeste de Puerto Rico, la cual se depositó alrededor de 31 millones de años atrás (MacPhee e Iturralde-Vinent, 1995). Los roedores que describimos en nuestro trabajo son similarmente antiguos, y juntos representan la evidencia más temprana de la presencia de perezosos terrestres y roedores caviomorfos en la región.

A lo largo del Mioceno se encuentran otros fósiles de vertebrados terrestres en la región de la Antillas Mayores, estos al igual que los del Oligoceno pertenecen a grupos que existieron durante el Pleistoceno. El Mioceno es el periodo geológico que le sigue al Oligoceno y que duró entre 23 a 5.3 millones de años. Estos fósiles del Mioceno incluyen perezosos terrestres, primates platirrinos, y hutías del Mioceno temprano de Cuba (MacPhee et al., 2003), una iguana y una boa del Mioceno medio de Puerto Rico (MacPhee y Wyss, 1990), al igual que varias especies de ranas, guecos y lagartijas del Mioceno medio de La Española (e.g. De Queiroz et al., 1998; Daza y Bauer, 2012). Como podrán notar la lista de fauna del Mioceno es más larga y diversa que la del Oligoceno. La ausencia de algunos de estos en los depósitos más antiguos se podría atribuir al registro fósil, el cual es imperfecto, ó podría ser una ausencia real, implicando que estos organismos llegaron más tarde durante otros eventos de dispersión luego de la fragmentación de GAARlandia (Dávalos, 2004). Por ejemplo, basándose en el registro fósil y relojes moleculares, se ha estimado que los primates platirrinos llegaron a la región durante el Mioceno temprano (Cooke et al., 2011; Kay, 2014). En comparación, el grupo de sapos endémicos de las Antillas Mayores, los cuales se les conoce con el nombre científico de Peltophryne (y es el grupo que incluye el sapo concho), tienen un registro fósil que solo se extiende al Cuatenario (Pregill, 1981). Sin embargo utilizando relojes moleculares se ha estimado que los sapos Peltophryne llegaron a la región caribeña mucho antes, durante el Eoceno tardío-Oligoceno temprano lo cual sería consistente con la hipótesis de GAARlandia (Alonso et al., 2012).

Así que como pueden ver, la evidencia que tenemos hasta ahora apunta a un origen más complicado de los vertebrados terrestres de las Antillas Mayores y parece que ambas hipótesis han jugado un rol en el origen de los mismos. Además, como mencionamos brevemente en nuestro trabajo, no todo tiene que haberse dispersado de Sur América a las Antillas. Por ejemplo, los gaviales gryposuquinos pudieron utilizar ese puente terrestre para dispersarse del Caribe a Sur América. Para lograr entender mejor esta complicada historia se necesita hacer más trabajo y más descubrimientos en la región. Trabajar en los trópicos no es fácil por la extensa vegetación y limitada exposición de las rocas, sin embargo, la recompensa es grande cuando se hacen descubrimientos como los que acabamos de publicar.


Referencias

Ali, J. R. 2012. Colonizing the Caribbean: is the GAARlandia land-bridge hypothesis gaining a foothold? Journal of Biogeography 39:431-433.
Alonso, R., A. J. Crawford, and E. Bermingham. 2012. Molecular phylogeny of an endemic radiation of Cuban toad (Bufonidae: Peltoprhyne based on mitochondrial and nuclear genes. Journal of Biogeography 39:434-451.
Anthony, H. E. 1918. The indigenous land mammals of Porto Rico, living and extinct. American Museum of Natural History, Memoirs 1(2):324-435.
Antoine, P.-O., L. Marivaux, D. A. Croft, G. Billet, M. Ganerod, C. Jaramillo, T. Martin, M. J. Orliac, J. Tejada, A. J. Altamirano, F. Duranthon, G. Fanjat, S. Rousse, and R. Salas Gismondi. 2012. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B 279:1319-1326.
Biknevicious, A. R., D. A. McFarlane, and R. D. E. MacPhee. 1993. Body size in Amblyrhiza inundata (Rodentia: Caviomorpha), an extinct megafaunal rodent from the Anguilla Bank, West Indies: estimates and implications. American Museum Novitates 3079:1-25.
Dávalos, L. M. 2004. Phylogeny and biogeography of Caribbean mammals. Biological Journal of the Linnean Society 81:373-394.
Daza, J. D., and A. M. Bauer. 2012. A new amber-embedded sphaerodactyl gecko from Hispaniola, with comments on morphological synapomorphies of the Sphaerodactylidae. Breviora 529:1-29.
De Queiroz, K., Ling-Ru Chu, and J. B. Losos. 1998. A second Anolis in Dominican amber and the systematics and ecological morphology of Dominican amber anoles. American Museum Novitates 3249:1-23.
Hedges, S. B., C. A. Hass, and L. R. Maxson. 1992. Caribbean biogeography: molecular evidence for dispersal in West Indian terrestrial vertebrates. Proceedings of the National Academy of Sciences of the United States of America 89:1909-1913.
Iturralde-Vinent, M. A., and R. D. E. MacPhee. 1999. Paleogeography of the Caribbean region: implications for Cenozoic biogeography. Bulletin of the American Museum of Natural History 238:1-95.
Kay, R. F. 2014. Biogeography in deep time – what do phylogenetics, geology, and paleoclimate tell us about early platyrrhine evolution? Molecular Phylogenetics and Evolution In press.
MacPhee, R. D. E., and M. A. Iturralde-Vinent. 1995. Origins of the Greater Antillean land mammal fauna, 1: new Tertiary fossils from Cuba and Puerto Rico. American Museum Novitates 3141:1-31.
MacPhee, R. D. E., and A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-45. 

Ortega-Ariza, D., E. K. Franseen, H. Santos-Mercado, W. R. Ramírez-Martínez, and E. E. Core-Suárez. 2015. Strontium isotope stratigraphy for Oligocene-Miocene carbonate systems in Puerto Rico and the Dominican Republic: implications for Caribbean processes affecting depositional history. Journal of Geology 123:539-560.
Pregill, G. 1981. Late Pleistocene herpetofaunas from Puerto Rico. University of Kansas Museum of Natural History Miscellaneous Publication 71:1-72.
Turvey, S. T., F. V. Grady, and P. Rye. 2006. A new genus and species of ‘giant hutia’ (Tainotherium valei) from the Quaternary of Puerto Rico: an extinct arboreal quadruped? Journal of Zoology 270:585-594.
Velez-Juarbe, J., T. Martin, R. D. E. MacPhee, and D. Ortega-Ariza. 2014. The earliest Caribbean rodents: Oligocene caviomorphs from Puerto Rico. Journal of Vertebrate Paleontology 34:157-163.
Woods, C. A., and F. E. Sergile (eds.). 2001. Biogeography of the West Indies: Patterns and Perspectives, second edition. CRC Press, Boca Raton, Florida, 608 pp.

Its January 2014, and with it comes the first issue of the Journal of Vertebrate Paleontology. There are many interesting papers, including several ones on fossil marine mammals, which are a frequent subject in this blog. However this post will be about another paper in that same issue, where several of my colleagues and myself describe fossil rodents from Puerto Rico (Velez-Juarbe et al., 2014). These are not just any fossil rodents, they are the oldest evidence of caviomorph rodents in the Greater Antilles, and help us further understand the timing of arrival of terrestrial vertebrates to the region, an issue which has been the matter of debate for several decades now (keep reading).
An account of fossil rodents from Puerto RicoIt’s not the first time that fossil rodents have been found in Puerto Rico. In fact, it is well known that during the Pleistocene, Puerto Rico, Hispaniola, Cuba, Jamaica, and several of the Lesser Antilles, were home to endemic groups of rodents and other land mammals (Woods and Sergile, 2001). Many of these Pleistocene mammals were described in the early 1900’s (e.g. Anthony, 1918), although there have been some more recent discoveries as well (Turvey et al., 2006). Some of the rodents included giant forms, with some, like Amblyrhiza inundata, had body masses similar to those of the American black bear (Biknevicious et al., 1993)! During the Pleistocene Puerto Rico was home to about  two or three species of heteropsomine spiny rats (Echymyidae), and possibly two species of plate-tooth (Heptaxodontids). A third group that is still present in the region, are the Capromyids, but these, apparently, never reached Puerto Rico. All of these groups of rodents, are part of a larger, more inclusive group of rodents known as caviomorphs. caviomorphs are endemic to South America, their ancestors arriving from Africa about 54 million years ago (Antoine et al., 2012). Once in South America caviomorphs underwent an explosive radiation, spreading throughout the continent and as we now know, the Caribbean, early on in their evolutionary history. A similarly fast radiation also happened with South American primates (Platyrhines) (Kay, 2014), which share a comparable history to that of the caviomorphs.This picture is from last week, when I revisited the Lares limestone site where i found the rodent incisor.The new fossils from Puerto Rico consist of a couple of isolated incisors, one from the early Oligocene San Sebastian Formation (from this locality), and the other from the late Oligocene Lares Limestone (from this locality; also see picture above). When I found the first fossils back in 2005, I contacted Ross MacPhee, curator of mammals at the American Museum of Natural History, and who has had a long interest in the origins of the Greater Antillean land mammal fauna. Based on what we know about the fossil record of Puerto Rico, Ross and I suspected these incisors were from a caviomorph. However, we had a problem, as you can see in the picture below, isolated incisors are really hard to identify based only on external features, as they are very simple and lack the cusps, valleys and ridges that characterize their molars (this is true for nearly all mammals). We then thought about looking at the enamel microstructure, as it does preserved features that can be extremely useful in identifying isolated finds like ours. Studying the enamel microstructure usually involves making cross-sections of the teeth, the cut surfaces are polished, etched in a light acid, and observed with the aid of scanning electron microscope (SEM's). To do this, we decided to contact Thomas Martin at Universität Bonn, an authority on enamel microstructure. After recruiting Thomas, we sent him the fossils, and within several months, he emailed us back with the description and interpretation of the fossils. Lateral (left) and anterior (right) views of the San Sebastian caviomorph incisor. Here the fossil was still partially surrounded by rock and had not been sectioned to study the enamel microstructure. Figure 2 from our paper. Here we show the cross section outline and the enamel microstructure of the San Sebastian caviomorph (left column) and Lares caviomorph (right column).Our fossils did belong to a caviomorph, thus confirming our initial suspicions and excitement about the discovery. Because of the importance of these fossils, we wanted to get as precise dates on the localities as possible, so I contacted my friend and colleague Diana Ortega-Ariza, a PhD candidate at the University of Kansas. For her masters at the University of Puerto Rico, Diana studied several of the limestone units in Puerto Rico, including the Lares Limestone. As part of her study, she obtained radiometric dates using isotopic signals preserved in the calcitic tubes that serve as home to the bivalve Kuphus incrassatus, which is commonly found in Oligocene through Miocene marine deposits. Based on the results she obtained, we are now able to say that the Lares Limestone was deposited between 27-24 million years ago during a geologic age called Chattian which is the youngest sub-division of the Oligocene. We could also used that timeframe to place deposition of the underlying San Sebastian Formation as older than 27 million years ago, or during the age known as Rupelian, the oldest subdivision of the Oligocene (the whole Oligocene period lasted between 33.9-23.0 million years ago).
Origins of the Greater Antillean land vertebrate fauna“The South American character of the West Indian mammals seems to indicate that this archipelago was formerly united to the southern continent, and that it has subsequently been an area of subsidence.” Charles R. Darwin The Voyage of the Beagle
That is one of my favorite sentences in Voyage of the Beagle. Charles Darwin never visited the Greater Antilles, but he was right about where did the mammals of the region originated. However, one of the long-standing questions regarding the origins of Greater Antillean land vertebrates is not where, but when did they arrived. For years the debate has been whether they arrived to the region at different intervals throughout the Cenozoic (e.g. Hedges et al., 1992) or in tandem during a single dispersal event (e.g. MacPhee and Iturralde-Vinent, 1995). The GAARlandia* hypothesis postulates that during the late Eocene-early Oligocene the islands of Cuba, Hispaniola and Puerto Rico together with the Aves Ridge formed a continuous, or nearly continuous landspan connected to northern South America (see figure below). This landspan, even though short-lived - it probably lasted between about 37.8 to 28.1 million years ago, or less - would have served as a corridor for the dispersal of land vertebrates into what eventually became the Greater Antilles (see Iturralde-Vinent and MacPhee [1999] for a very detailed overview of the geologic evidence). Ideally, we should be finding fossils representing the different groups of Pleistocene and recent Greater Antillean land vertebrates in late Eocene-early Oligocene deposits, and we do, at least in part. *Greater Antillean Aves Ridge land (MacPhee and Iturralde-Vinent, 1995)Figure 1 from our paper. Here we show the various localities (A) in South America where Eocene and Oligocene rodents are known and Domo de Zaza (DZ) in Cuba, where early Miocene rodents are known. In B are the localities in Puerto Rico, Río Guatemala (RG), and Lares Limestone (LL). C is the paleogeographic reconstruction of the Caribbean region during the late Eocene-early Oligocene. During this time Cuba, Hispaniola and Puerto Rico were joined with the Aves Ridge (C) forming a nearly continuous landspan connected to northern South America.The fossil record of the region has so far provided a few clues supporting this hypothesis as well. One of the first ones found was a femur (leg bone) of a ground sloth (megalonychid) in the early Oligocene Juana Diaz Formation in southwestern Puerto Rico which was deposited about 31 million years ago (MacPhee and Iturralde-Vinent, 1995). The rodents described in our work are just as old, and together they are the earliest evidence of these two groups in the region.Throughout the Miocene (the period between 23-5.3 million years ago) in the Greater Antilles there are other occurrences of terrestrial vertebrates that were present during the Pleistocene and some which are even still around today. There are early Miocene sloths, rodents and primates from Cuba (MacPhee et al., 2003), a boa and an iguana from the early Miocene of Puerto Rico (MacPhee & Wyss, 1990), as well as a number of frogs, geckos and anoles from the middle Miocene of Hispaniola (e.g. De Queiroz et al., 1998; Daza and Bauer, 2012). The absence of some of these groups in Oligocene rocks in the Greater Antilles could be due to the scarcity of the fossil record, or could indeed be real, implying that some of these groups arrived by random overwater dispersal after fragmentation of GAARlandia (Dávalos, 2004). For example, based on fossils and molecular data, primates have an estimated time of arrival to the region during the early Miocene (Cooke et al., 2011; Kay, 2014). On the other hand, toads of the genus Peltophryne which is endemic to the region, are known only from Pleistocene deposits (Pregill, 1981) but molecular estimates place their split from their closest relatives during the late Eocene-early Oligocene (Alonso et al., 2012).So, as you can see, the evidence seems to point to a more complex origin of the Greater Antillean land vertebrates and does not seem to favor one over the other. Also, not everything had to have come from South American to the Greater Antilles. As we mentioned briefly in our paper, organisms that were present in the Antilles, such as gryposuchine gavials, could have used that same corridor to disperse to the southern continent. Further unraveling of this complex history can only be achieved by more fieldwork and discoveries in the Greater Antilles. 
References
Ali, J. R. 2012. Colonizing the Caribbean: is the GAARlandia land-bridge hypothesis gaining a foothold? Journal of Biogeography 39:431-433.
Alonso, R., A. J. Crawford, and E. Bermingham. 2012. Molecular phylogeny of an endemic radiation of Cuban toad (Bufonidae: Peltoprhyne based on mitochondrial and nuclear genes. Journal of Biogeography 39:434-451.
Anthony, H. E. 1918. The indigenous land mammals of Porto Rico, living and extinct. American Museum of Natural History, Memoirs 1(2):324-435.
Antoine, P.-O., L. Marivaux, D. A. Croft, G. Billet, M. Ganerod, C. Jaramillo, T. Martin, M. J. Orliac, J. Tejada, A. J. Altamirano, F. Duranthon, G. Fanjat, S. Rousse, and R. Salas Gismondi. 2012. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B 279:1319-1326.
Biknevicious, A. R., D. A. McFarlane, and R. D. E. MacPhee. 1993. Body size in Amblyrhiza inundata(Rodentia: Caviomorpha), an extinct megafaunal rodent from the Anguilla Bank, West Indies: estimates and implications. American Museum Novitates 3079:1-25.
Dávalos, L. M. 2004. Phylogeny and biogeography of Caribbean mammals. Biological Journal of the Linnean Society 81:373-394.
Daza, J. D., and A. M. Bauer. 2012. A new amber-embedded sphaerodactyl gecko from Hispaniola, with comments on morphological synapomorphies of the Sphaerodactylidae. Breviora 529:1-29.
De Queiroz, K., Ling-Ru Chu, and J. B. Losos. 1998. A second Anolis in Dominican amber and the systematics and ecological morphology of Dominican amber anoles. American Museum Novitates 3249:1-23.
Hedges, S. B., C. A. Hass, and L. R. Maxson. 1992. Caribbean biogeography: molecular evidence for dispersal in West Indian terrestrial vertebrates. Proceedings of the National Academy of Sciences of the United States of America 89:1909-1913.
Iturralde-Vinent, M. A., and R. D. E. MacPhee. 1999. Paleogeography of the Caribbean region: implications for Cenozoic biogeography. Bulletin of the American Museum of Natural History 238:1-95.
Kay, R. F. 2014. Biogeography in deep time – what do phylogenetics, geology, and paleoclimate tell us about early platyrrhine evolution? Molecular Phylogenetics and Evolution In press.
MacPhee, R. D. E., and M. A. Iturralde-Vinent. 1995. Origins of the Greater Antillean land mammal fauna, 1: new Tertiary fossils from Cuba and Puerto Rico. American Museum Novitates 3141:1-31.
MacPhee, R. D. E., and A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-45. 
Pregill, G. 1981. Late Pleistocene herpetofaunas from Puerto Rico. University of Kansas Museum of Natural History Miscellaneous Publication 71:1-72.
Turvey, S. T., F. V. Grady, and P. Rye. 2006. A new genus and species of ‘giant hutia’ (Tainotherium valei) from the Quaternary of Puerto Rico: an extinct arboreal quadruped? Journal of Zoology 270:585-594.
Velez-Juarbe, J., T. Martin, R. D. E. MacPhee, and D. Ortega-Ariza. 2014. The earliest Caribbean rodents: Oligocene caviomorphs from Puerto Rico. Journal of Vertebrate Paleontology 34:157-163.

Woods, C. A., and F. E. Sergile (eds.). 2001. Biogeography of the West Indies: Patterns and Perspectives, second edition. CRC Press, Boca Raton, Florida, 608 pp.

This will be, for now, the final part of this series. This is going to be a bit of a tease, as I'll go over some of the cetacean find we've made in the last several months won't go into many details as to what each of the fossils are. That will be the subject of future posts, once the fossils are properly described and published. There are a good amount of pictures to make up for it, so enjoy!

Trash road cetacean
As you may have read previously (here, here and here) collecting fossil vertebrates in the Chagres Formation is not an easy task and takes some planning before collecting each specimen. Back in the summer I found what seemed to be the remains of a fossil cetacean partially exposed on on the wave cut platform (see pictures below). To get to this locality we had to walk through a 10 meter stretch of road that is always full of trash, hence the locality name. As for the fossils, not a lot of it was exposed, and the day when we found it, we were on another mission. So we ended going back to the site to collect the fossils two days before Thanksgiving Day, and like most other digs here, we only had about four hours before the high tide took over.
Left: The exposed fossil; right: Chris (Summer 2013 intern) looking at it somewhat in disbelief. Finally, in November we collected the fossil. James and I started digging the trench around the fossil, soon after the other interns joined the digging party.Zach, Sarah, Elena and James (Fall 2013 interns) are happily posing with the jacketed fossil, it only took us about 2 and a half hours. And liftoff!! We take the jacket to the truck and off to STRI where it will be properly prepared.

Chagres Norte dolphin
Back in early September, I had the chance to go prospecting in the Chagres Formation with two of my colleagues from invertebrate paleontology at the Florida Museum of Natural History, Roger Portell and Austin Hendy. They've previously done some more work in the marine units here in Panama, so it was good to go out with them and see new localities. One of these, was located further north of the village of Piña than I'm used to. Getting there involved a really muddy road, fortunately, we had all terrain vehicles, and it was actually fun driving through it.The site, which I dubbed Chagres Norte, was one of the northern-most localities near the village of Piña.At this site as with others along this whole coast, the Chagres Formation is exposed along the wave-cut platforms and sea cliffs. One of the fossils we knew was there (Roger and Austin had found it some days earlier) was part of the vertebral column of a small cetacean.Elena (Fall 2014 intern), Roger and Austin collect the cetacean vertebrae. This is one of the reasons I like these guys, even of they specialize in invertebrates, they know not to ignore vertebrate fossils and will collect them.

This was Elena's second day in the field. She got hooked on the Chagres and even "claimed" the fossil saying that she was going to do the prep work, which she did.The partial vertebral column we collected back in September. This is after Elena's careful and fantastic prep job.Chagres Sur odontocete
Later that day, we went to another locality, this one south of Piña, so I gave it the obvious name of Chagres Sur. At this site I spotted some cetacean fossils sticking out of the sea cliff (see picture below).One of the localities south of Piña, where I spotted some cetacean bones (you can see the bones towards the center right). For reasons I can't remember, Elena is staring in the wrong direction.At that point, I didn't know what this fossil was, and we were also running out of daylight, so we left it there, and hoped to come back another day to collect it. It wasn't until a couple of weeks ago (1st week of December), that I decided to re-visit the locality with the interns. It was then, upon seeing this fossil again, that I had one of those, aha! moments and I realized what it was. So we had to collect it!Here I am with the Chagres Sur odontocete, just before we removed it.I won't go into details of what the fossil is at this moment (I warned you this was a post to spark your curiosity). But, if you plan on attending the 10th North American Paleontological Convention in Florida next February, you'll definitely find out more about it!
So stay tuned, you'll hear more about these discoveries in 2014!

The previous post was to give you a brief introduction into the geology of the Chagres Formation, which is where we are focusing part of our collecting efforts. This next post is to give you an idea of what happens when we find fossils of large marine vertebrates in the Chagres.

Often, when we find fossils in the Chagres these are on the rock exposed in the wave-cut platform along the beach (although there are exceptions). The benefit of this is the relatively easy access, the downside, is that we usually have only about 4 hours (spanning between the period before, during and after, the low tide) to collect the fossil. Back in April, during one of our trips to the Caribbean coast, we saw a partial marlin mandible exposed on one of the wave-cut platforms (picture below). That day we were prospecting, that is, looking for new localities and new fossils that were exposed so that we could plan to collect them in the near future. This was one of those finds.
A partial marlin mandible exposed on the wave-cut platform (anterior to the left).The near future ended up being July. And so it was that together with Carlos De Gracia (a STRI intern whose main interest are fossil fishes), and my summer 2013 interns, Chris, Christina, and Silvia (previously featured here) we set out to the Caribbean to collect that fossil marlin.

Collecting the fossil took us three days. The first day was cut short and we couldn't do much work as the weather turned bad, and we had to leave after about an hour of work. Day two was purely devoted to digging a trench around the fossil so that we could wrap it in a protective plaster jacket for proper removal and transportation back to STRI (see picture below). This is a near obligatory task and method of proper collection of fossil vertebrates and has been used at least  since the late 1800's. While digging around it, we realized that we had more than we thought, the fossil consisted of mandible and skull, which meant we had to dig deeper, and wider around the fossil to be able to remove it completely.
Day 2 of the excavation. From left to right: Carlos De Gracia (STRI intern) and my summer 2013 interns, Christina, Chris and Silvia, make the trench around the marlin skull and mandible.After we dug a deep enough trench around the fossil, we were ready to put a plaster jacket around it. Except that by then it was late, and the tide was coming back in, meaning we had to jacket the specimen another day. Finally, on our third day at this particular site, were were able to put a jacket around the fossil (see pictures below).Day 3 of the excavation. Christina and Silvia are finish the jacket protecting the marlin skull and mandible.This is the locality, if you click on the image you can see Silvia (near the center) and Christina (to the right); behind her is the jacket (the white blob on the ground).After the plaster dried we undercut the block and flipped it so that we could remove excess rock and make it a bit lighter to carry back to the truck and then drive back to STRI (see pictures below). This specimen, as well as several other marlins that have been collected from the Chagres (including the one mentioned here), will be prepared and studied by Carlos.
After we popped and overturned the jacket,  me, Chris, and Carlos removed some of the excess rock in order to make it lighter.Liftoff!! Even after trimming some of the rock off, this was still a pretty heavy block.Other fishes known from the Chagres include a variety of bony fishes (mainly know from otoliths, which I mentioned in Part 1) as well as a several species of sharks (of which cookie-cutter sharks are one of the most common). Marlins are also relatively common and easy to recognize in the field; in fact, this year alone, we have collected several other skulls, mandibles and vertebrae.
Because they are common, the fossil marlins of the Chagres have not gone unnoticed, unlike the marine mammals. In 1978, Harry L. Fierstine described the first fossil marlin known from Panama. The fossil, consisting of a nearly complete skull, represented a new species, which he named Makaira panamensis. Modern relatives of Makaira panamensis include the black and the blue marlins. A second fossil marlin from Panama was described in 1999 (Fierstine, 1999). This one was found in the late Miocene Gatun Formation, which underlies the Chagres Fm. The fossil consisted of a partial rostrum, and was identified as Makaira cf. M. nigricans, the same species as the blue marlin (Fierstine, 1999). This implies that this particular species has been around for several million years, or more likely, that some extant members of this group are morphologically conservative and show very little differences from its fossil relatives.  
I'm sure we'll learn more about the fossil fishes of the Chagres and Gatun formations in the not so distant future. For now, stay tuned as this series is not yet over!

Literature Cited
Fierstine, H. L. 1978. A new marlin, Makaira panamensis, from the Late Miocene of Panama. Copeia 1978:1-11.
Fierstine, H. L. 1999. Makaira sp., cf. M. nigricans Lacépede, 1802 (Teleostei: Perciformes: Istiophoridae) from the Late Miocene, Panama, and its probable use of the Panama Seaway. Journal of Vertebrate Paleontology 19:430-437.

After a few years, I thought it was fair to change the look of the blog a little bit. If you look up I've changed the banner, to one thats better (I think) and less crowded than the previous one. The pictures on the new title banner are all from different localities I've been doing fieldwork over the last couple of years and expect to continue to do so.

As for the old one, here's what was in it.
1) Pleistocene beach deposits in Isabela, Puerto Rico2) Illustration of the skull of a new dugongid taxon (more on this in 2014)3) Portunid crab from the San Sebastian Formation4) Cross-bedded sandstones of the San Sebastian Formation5) Tooth of Physogaleus contortus from the Lares Limestone6) Tooth of Hemipristis serra from the Juana Diaz Formation7) Outcrop of the Lares Limestone along road 111 in San Sebastian, Puerto Rico8) Illustration of the skull of Dugong dug on showing the muscle attachment sites, modified from Domning (1977)9) Mandible of Nesophontes edithae, one of several extinct Pleistocene mammals from PR 
Of course, feel free to guess where the pictures in the new banner were taken and leave your comments below. Good luck!!

Its been quite a while since the last post here at Caribbean Paleobiology. Lots of traveling and working hard on publishing parts of my dissertation as well as my current research projects here in Panama (stay tuned for more on this next year) have kept me extremely busy.

As I have mentioned previously, my work during this postdoc requires that I lead a group of interns (you can learn more about the internship here) as we search for terrestrial vertebrates in early Miocene deposits exposed on the Pacific side of the Panama Canal (see previous post). However, every now and then, as you may have seen in previous posts (here and here), we get to go to the Caribbean side of Panama in search of late Miocene marine vertebrates in the Chagres Formation. This is the first part of a series about our recent efforts to collect fossil marine vertebrates and to better understand the geology of the Chagres Fm.
Map of the northern part of the Panama Canal Basin. Here you can see the extension of the Chagres Formation and its members (map from Collins et al., 1996). (Click on the image to see a larger version.)
The Chagres Formation
This formation, exposed on the northern part of the Panama Canal Basin (see map above), generally consist of three distinct members or facies: Toro Member, silty sandstone facies, and Rio Indio facies (Collins et al., 1996). Age estimates for the deposition of the Chagres have been made using Foraminifera (which are extremely good index fossils). As a result, we known that the formation was deposited between 8.6-5.6 million years ago (Collins et al., 1996), during the final part of a geologic period known as the Miocene.
Toro Point, located southwest of the Caribbean exit of the Panama Canal, located within Ft. Sherman, which is a former US military base.The Toro Member is the basal unit of the formation, and consist of cross-bedded coquinas and medium to coarse sands (see picture below). Coquina, is a term used to describe a sedimentary deposit that consists mostly, if not entirely, of shell fragments. In the case of the Toro Member, it is made up almost entirely of echinoid (sea urchin) and barnacle fragments, together with other less common bivalves and gastropods. Both, the types of invertebrates that make up the coquina, as well as the cross-bedding is indicative of high-energy, shallow marine habitats (Hendy, 2013)
Cross beds of the Toro Member, as exposed in Toro Point.Disregarding what the geology and macroinvertebrates suggest, the Toro Member has been interpreted as being deposited at much deeper depths (several hundreds of meters), by a high-energy stream flowing from the Pacific Ocean towards the Caribbean sea, and thus representing the final connection between these two oceans (Collins et al., 1996). This interpretation, is based on the occurrence of deep-water fossils of Pacific affinities within the silty sandstone facies.
The silty sandstone facies of the Chagres Formation, as exposed in Playa Tortuguilla, located northeast of Fuerte San Lorenzo, and the mouth of the Chagres River. From left to right: James, Sarah, Elena and Zach (Fall 2013 interns) are studying the trace fossils of the Chagres. About 4-5 kilometers southwest of Toro Point, is where the main part of the Chagres Formation, the silty sandstone facies, is exposed. This is the most extensive of the members, going from southwest of Toro Point to about ~6 kilometers southwest of the village of Piña. Foraminifera (or forams for short) are not only used for estimating when marine units were deposited, but can also serve as index fossils for depositional depth, and environment. Forams collected from the silty sandstone facies of the Chagres were used for estimating the depth of this part of the formation, resulting in an estimate of somewhere between 200-500 meters (Collins et al., 1996).
Outcrop of the silty sandstone facies of the Chagres Formation near the village of Piña.Forams are not the only fossils known from these units. Fierstine (1978) described a fossil marlin which he dubbed Makaira panamensis, an extinct species only known from this place and time. Other fossils found in these facies are fish otoliths. Otoliths are fish ear bones; they can be identified fairly accurately, and, similar to forams, they can be used as index fossils. A preliminary study of the otolith fauna of the silty sandstone facies collected near the village of Piña, suggests that these facies were deposited somewhere between 100-700 meters (De Gracia et al., 2012). This is a broader estimate, than that obtained using the forams, but still consistent with the idea that the silty sandstone facies represent relatively deep marine environments. These units, have so far, proven to be the most productive in terms of vertebrate fossils, thus most of our efforts have been in this area. In fact, back in 2011, I was near Piña, collecting a fossil dolphin* as part of the Pyenson Lab, and, more recently, with the Spring 2013 interns we collected a fossil sperm whale and parts of a marlin skull. (More about even more recent discoveries in the following iterations of this series).
*You can see more of the fossil dolphin collected during the Pyenson Lab 2011 expedition here!
Outcrop of the Río Indio facies of the Chagres Formation, somewhere south of La Boca del Indio. Towards the southwest, along the opposite site of the basin, between Palmas Bellas and Rio Gobea, is where we find the Rio Indio facies. These facies are characterized by siltstones and sandstones (Collins et al., 1996). Estimates of the depositional environment of these facies are variable, but generally much shallower than those of the silty sandstone facies (see below). Based on forams, it ranged from 50-80 meters, whereas estimates based on fish otoliths (= fish ear bones) it ranges from 0-100 meters (Collins, 1996; Collins et al., 1996; Aguilera and Aguilera, 1999). Just today was our first time visiting some of the Río Indio localities, and although we didn't find any vertebrates, we did find mollusks which are consistent with the shallower depth interpretations of previous workers.

So, stay tuned for the upcoming installments of this series!


Literature Cited

Aguilera, O., and D. R. de Aguilera. 1999. Bathymetric distribution of Miocene to Pleistocene Caribbean teleostean fishes from the coast of Panama and Costa Rica. Bulletins of American Paleontology 357:251-270.

Collins, L. S. 1996. Environmental changes in Caribbean shallow waters relative to the closing Tropical American Seaway; pp. 130-167, in J. B. Jackson, A. Budd, and A. Coates (eds.), Evolution and Environment in Tropical America. University of Chicago Press, Chicago, Illinois.

Collins, L. S., A. G. Coates, W. A. Berggren, M.-P. Aubry, and J. Zhang. 1996. The late Miocene Panama isthmian strait. Geology 24:687-690.

De Gracia, C., J. Carrillo-Briceño, W. Schwarzhans, and C. Jaramillo. 2012. An exceptional marine fossil fish assemblage reveals a highly productive deep-water environment in the Central American Seaway during the late Miocene. Geological Society of America Abstracts with Programs 44:164.

Fierstine, H. L. 1978. A new marlin, Makaira panamensis, from the late Miocene of Panama. Copeia 1978:1-11.

Hendy, A. J. W. 2013. Spatial and stratigraphic variation of marine paleoenvironments in the middle-upper Miocene Gatun Formation, Isthmus of Panama. Palaios 28:210-227.

Soon after the last post, I headed out to the US, for a short collection trip. During this trip, I visited both the Florida Museum of Natural History (FLMNH), and the National Museum of Natural History (NMNH) as I needed to compare my notes on some fossil cetaceans from the late Miocene of Panama with material housed in those institutions. It was also an opportunity to see my wife as well as spend some quality time with some good friends.

Gainesville, FL
At the Florida Museum of Natural History, I focused on comparing the Panamanian material with several fossil toothed whales in the collections, mainly from the late Miocene and early Pliocene of Florida. There are some interesting specimens at the FLMNH and I was able to make some useful comparisons. I also took some time to look at the exhibits in the museum, which I had not fully done yet.
Me, pointing out to the Florida dugongid triad, of which I wrote early last year (Vélez-Juarbe, et al., 2012). These are part of one of the exhibits at the Florida Museum of Natural History. Not everyday you get to see fossils you've worked on as part of an exhibit. One of those is a new species, so stay tuned!!
Washington, DC
At the Smithsonian in Washington, DC, I had the opportunity to look at both extant and fossil whales. For this, I went to the Smithsonian's Museum Support Center (MSC) which is where the extant whales are housed. If you study whales and dolphins of any kind, this is the place to go! The collection at the MSC allows us to look at more than one individual of a certain species, which gives us a better understanding of differences in the morphology due to age (juveniles vs adults) or sex (males vs females), or just variation within a species. We need to know this, specially when it comes to describing fossil species.
The "whale warehouse", one of the several storage facilities at the Smithsonian's Museum Support Center. If you need to look at skeletons of extant whales, this is the place to go!The skull of Bohaskaia monodontoides a fossil beluga which Nick Pyenson and myself described last year (Vélez-Juarbe & Pyenson, 2012). Now part of a temporary exhibit called "Whales: From Bone to Book". Make sure you see it if you're in the DC area, its awesome!!I also looked at several fossil whales, mostly physeteroids, which is the group that include sperm whales and pygmy sperm whales.
Some of the fossil whale I studied at the NMNH. Left: cast of the skull of Aulophyseter morricei, a small sperm whale from the middle Miocene of California (Kellogg, 1927). Right: the skull of Aprixokogia kelloggi, a fossil pygmy sperm whale from the early Pliocene of North Carolina (Whitmore & Kaltenbach, 2008).Panama
After the US tour, I returned to Panama. Fieldwork so far, has been pretty standard along the canal. One of the recent highlights, was the visit of Bruce MacFadden, who brought a fantastic group of school teachers from California and Florida. We all did some fieldwork along the canal and also went to some localities of the Gatun Formation. At one of the Gatun localities the teachers had prepared an in situ paleontological workshop for a group of local schoolchildren, which was a wonderful experience for all of us involved!
The students were measuring diversity within a meter square grid.It was not all fieldwork. We also had the chance to go birdwatching along the Pipeline trail in Gamboa, where we did get to see several birds, as well as a lot of other fauna along the trail.
On our hike along the Pipeline trail, led by George Angehr of the BioMuseo, and also author  of Birds of Panama (an excellent reference).
Some of the fauna we saw along the Pipeline trail. Clockwise from top left: leaf beetle (Platyphora haroldi); brown-throated three-toed sloth (Bradypus variegatus); black-tailed trogon (Trogon melanurus); striped rocket frog (Silverstonneia flotator).So I guess that's it for now. But stay tuned as more discoveries are made in the canal and elsewhere here in Panama!


References
Kellogg, R. 1927. Study of the skull of a fossil sperm-whale from the Temblor Miocene of southern California. Carnegie Institution of Washington Publication 346:1-23.

Vélez-Juarbe, J., and N. D. Pyenson. 2012. Bohaskaia monodontoides, a new monodontid (Cetacea: Odontoceti: Delphinoidea) from the Pliocene of the Western North Atlantic Ocean. Journal of Vertebrate Paleontology 32:476-484.

Vélez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages in the past ~26 million years. PLoS ONE 7(2):e31294.

Whitmore, F. C., Jr., and J. A. Kaltenbach. 2008. Neogene Cetacea of the Lee Creek Phosphate Mine, North Carolina; pp. 181-269 in C. E. Ray, D. J. Bohaska, I. A. Koretsky, L. W. Ward, and L. G. Barnes (eds.), Geology and Paleontology of the Lee Creek Mine, North Carolina, IV. Virginia Museum of Natural History Special Publication 14.

A little more than a month ago I got an email regarding a fossil find near the construction site of the new canal locks on the Atlantic side of Panama. The photo that came with the email was a bit blurry and with no scale, so it could as well be a small fossil, or even an invertebrate. However, I took the chance as it was, after all, an opportunity to look at outcrops on that part of the canal (most of our work is towards the Pacific side). And so it was, that the spring interns (previously featured here and here) and myself ended up driving towards Colón with the hopes that the fossil was some sort of interesting vertebrate.

One thing I must mention, is that security is very tight in the canal, much more so near the construction sites. So that day, we only had about 20 minutes to look at the fossil and eventually come up with a plan to collect it at some later time, if it was worth it.

And it was! Upon seeing the fossil, I immediately recognized it as a baleen whale jaw. Most of what we could see was a cross section of it (see below), which meant that however long the jaw was, it was going straight into the wall.
Part of a baleen whale jaw, in cross section.It is not the first time that fossil whales have been found in Panama. A 2010 paper by Mark Uhen of George Mason U. and colleagues (including yours truly) described all that was known of the fossil marine mammals of Panama. Admittedly, it wasn't much, but we were able to confirm the presence of dugongid sirenians, toothed whales (odontocetes) and baleen whales (mysticetes) (Uhen et al., 2010).   Since then, more and better material has been found, including a couple of odontocete skulls that I have helped collect from the late Miocene Chagres Formation (see here and here), as well as other things you'll hear about later this year at SVP.

The new whale mandible was found in the Gatun Formation of late Miocene (12-8 Ma) age (Collins et al., 1996). The Gatun is better known for the abundance of invertebrates (e.g. Woodring, 1957; Hendy, 2013) and for having deposits that represent nursery sites for Carcharocles megalodon (Pimiento et al., 2010). Previous reports of whales from the Gatun include odontocete ribs (Uhen et al., 2010), so finding a baleen whale is a first!

Like I mentioned above, that day we only had a very limited amount of time, and the fossil was worth rescuing. And so it was that over the next month or so I began coordinating with the Panama Canal Authority to go back and collect the fossil. Just last week we were able to go back. This time I had a new group of interns, and over the course of two days we were able to collect the fossil.

The summer interns at the dig site. Chris (at far left) prospects, while Christina and Silvia dig around the whale jaw.  You can see the construction of the new locks in the background.Unfortunately, due to the nature of the outcrop we only had a limited space and depth to dig. So we had to make the best out of it. Sadly, that meant that if the jaw was longer than our depth limit, we had break it.
The whale jaw, prior to being jacketed.
Me posing with the now jacketed whale jaw fragment. 
The exact affinities of the whale jaw remain a mystery, for now. Hopefully once it is prepared I'll be able to determine what it is. So stay tuned!


References

Collins, L. S., A. G. Coates, W. A. Berggren, M.-P. Aubry, and J. Zhang. 1996. The late Miocene Panama isthmian strait. Geology 24:687-690.

Hendy, A. J. W. 2013. Spatial and stratigraphic variation of marine paleoenvironments in the middle-upper Miocene Gatun Formation, Isthmus of Panama. Palaios 28:210-227.

Pimiento, C., D. J. Ehret, B. J. MacFadden, and G. Hubbell. 2010. Ancient nursery area for the extinct giant shark Megalodon from the Miocene of Panama. PLoS ONE 5(5):e10552.

Uhen, M. D., A. G. Coates, C. A. Jaramillo, C. Montes, C. Pimiento, A. Rincón, N. Strong, and J. Velez-Juarbe. 2010. Marine mammals from the Miocene of Panama. Journal of South American Earth Sciences 30:167-175.

Woodring, W. P. 1957. Geology and paleontology of Canal Zone and adjoining parts of Panama. Geology and description of Tertiary mollusks (gastropods: Trochidae to Turritellidae). U.S. Geological Survey Professional Paper 306-A:1-146.

Its been a while since I posted news on fossil sirenians. I've been very busy with fieldwork, manuscripts, among other things. The Spring interns have now gone back home. So, while I wait for the arrival of the next round of interns, here's the latest on fossil sirenians.


Where are sirenians found

With the exception of the now extinct Steller's seacow (Hydrodamalis gigas), all extant sirenians have tropical to subtropical distribution, with some species having a notably broad latitudinal and longitudinal distribution (Marsh et al., 2011). But, when we look at the fossil record of sirenians, we see a slightly different pattern of distribution, mostly tied to tectonic and/or climatic events. For example, during parts of the Cenozoic global temperatures were higher than today (Zachos et al., 2001), so you find fossils of sirenians far off their modern range (e.g. Belgium). These climatic variations amongst other physical drivers have played a prominent role in the distribution of seagrasses and seacows (expect more on this in the nearby future).

Nowadays, in the Western Atlantic and Caribbean (WAC) region, the most common and widespread sirenian is the West Indian Manatee (Trichechus manatus) whose range extends from as far north as the Carolina's (with some individuals reaching New England) to northeastern Brazil; another species found in the region is the Amazonian manatee (Trichechus inunguis) which lives in the Amazon basin (see map below). But, it hasn't always been like this. Throughout most of the Cenozoic, dugongids, a group of sirenians are now restricted to the Indo-Pacific region, were the predominant seacow group in the WAC, including multispecies communities in the region (Domning, 2001; Velez-Juarbe et al., 2012a; see previous post on this subject). Fossil of dugongids in the WAC are found in deposits as far north as Maryland, and as far south as Argentina. However, these southernmost dugongids, are poorly known, and have had a somewhat rocky taxonomic history.


From Metaxytherium to Dioplotherium a case of mistaken identity

The most common, and temporally and geographically widespread seacow genus known is the Halitheriine dugongid Metaxytherium. Species of this genus are known from late Oligocene through Pliocene deposits, and are found from the Eastern Pacific, Caribbean, Western and Northern Atlantic, and Western Tethys regions (e.g. Domning, 1988; Sorbi et al., 2012). Therefore it shouldn't have been much of a surprise when Roy H. Reinhart (1976) described a molar from the late Miocene Paraná Formation of Entre Ríos, Argentina as that of Metaxytherium. The importance of this find, lies in that prior to its discovery, the youngest species of Metaxytherium known from the WAC was the middle Miocene M. floridanum, which is not known outside of Florida (Domning, 1988). The Paraná molar was then, the youngest and southernmost record of the genus from the Western Atlantic.

However, species of Metaxytherium display a generally conservative morphology, and because of this, it has had a long, somewhat convoluted, taxonomic history. This is, fortunately, slowly being resolved as most species of Metaxytherium have been re-described (e.g. Domning, 1988; Domning & Pervesler, 2001; Sorbi et al., 2012) and studied in detail within the last 25 years, giving us, paleosirenologist a better idea of the valid species within the genus and variation within each species. Since Reinhart's description, several workers (Cozzuol, 1996; Cione et al., 2000; Domning, 2001) have disagreed with his interpretation regarding the affinities of the Argentinian molar. All of them referring the Paraná molar to Dioplotherium, still a dugongid, but one that belongs to the Dugonginae, a group very different from that to which Metaxytherium belongs. And indeed, the overall morphology of the tooth conforms well with what we know about Dioplotherium, it is in fact, very similar to those of Dioplotherium cf. D. allisoni from the early Miocene of Brazil (Toledo & Domning, 1991). This meant that Metaxytherium may have gone extinct in the WAC at the end of the middle Miocene (Domning, 1988), and that the genus only reached as far south as northeastern Brazil (Toledo & Domning, 1991), or did it?

Left: Map showing the distribution of Miocene seacows throughout the Americas. (ER = Entre Ríos).
Right: Map showing the distribution of extant sirenian in the Americas.
(Click on the map to view larger version.)

New fossils from the Paraná Formation

A couple of years ago I received an email from an Argentinian colleague, Jorge Noriega from CONICET in Diamante, informing me of a new discovery from the Paraná Formation in Entre Ríos. The new fossils consisted of left and right partial maxillae and most of the molars of a single individual (see figure below). At this point I was close to finishing my PhD, which meant that I had look at a lot of specimens and was well acquainted with the morphology of most, if not all Oligocene through Pliocene sirenians. Once I looked at the pictures of the new material, I quickly recognize these as most likely representing a species of Metaxytherium.
Molars of Metaxytherium from the late Miocene Paraná Formation. 1-2) left maxilla and M1-3 in occlusal view. 3-4) right maxilla and M3 (modified from Velez-Juarbe et al., 2012b)Now, I must admit that dugongid teeth are not the most diagnostic, so figuring out if these actually belonged to Metaxytherium was not an easy and quick task. After a considerable amount of reading, and detailed observations of material from various species of Metaxytherium as well as other dugongids I was confident they belonged to that genus. And so, working together with Jorge and Brenda Ferrero (also from CONICET in Diamante) we took on the task of formally re-designating the fossil described by Reinhart (1976) as well as describing the new material which actually represented a species of Metaxytherium (Velez-Juarbe et al., 2012b). The new Parana molars are quite similar to those of the middle Miocene Metaxytherium floridanum, but, their dimensions are below the range exhibited by M. floridanum and may represents a different species. One of the positive outcomes resulting from this work, was realizing that teeth of dugongids can sometimes be of taxonomic usefulness. We noticed, that the molars of some of the more derived species of Metaxytherium often have additional cusp and/or cuspules, a derived character which is not observed in Dioplotherium or any of its kin (i.e. Dugongines). The contemporaneous presence of both, Dioplotherium and Metaxytherium is not something unheard of. This same duet, occurs in the late Oligocene of Florida, early Miocene of Brazil and possibly in the middle Miocene of California and Baja California (Domning, 2001; Velez-Juarbe et al., 2012a). This again shows that multispecies communities and niche partitioning seems to have been the norm, not the exception, throughout sirenian history.


References

Cione, A. L., M. M. Azpelicueta, M. Bond, A. Carlini, J. Casciotta, M. A. Cozzuol, M. de la Fuente, Z. Gasparini, F. Goin, J. Noriega, G. Scilato-Yané, L. Soibelzon, E. Tonni, D. Verzi, and M. G. Vucetich. 2000. Miocene vertebrates from Entre Ríos Province, Argentina. INSUGEO, Serie Correlación Geológica 14:191-238.

Cozzuol, M. A. 1996. The record of the aquatic mammals in southern South America. Münchner Geowissenschaftliche Abhandlungen A30:321-342.

Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:295-426.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 1:27-50.

Domning, D. P., and P. Pervesler. 2001. The osteology and relationships of Metaxytherium krahuletzi Depéret, 1895 (Mammalia: Sirenia). Abhandlungen der Senckenbergischen Naturforschenden Gessellschaft 553:1-89.

Marsh, H. D., T. J. O'Shea, and J. E. REynolds, III. 2011. Ecology and conservation of the Sirenia: dugongs and manatees. Cambridge University Press, 521p.

Reinhart, R. H. 1976. Fossil sirenians and desmostylids from Florida and elsewhere. Bulletin of the Florida State Museum, Biological Sciences 20:187-300.

Sorbi, S., D. P. Domning, S. C. Vaiani, and G. Bianucci. 2012. Metaxytherium subapenninun (Bruno, 1839) (Mammalia, Dugongidae), the latest sirenian of the Mediterranean Basin. Journal of Vertebrate Paleontology 32:686-707.

Toledo, P. M., and D. P. Domning. 1991. Fossil Sirenia (Mammalia: Dugongidae) from the Pirabas Formation (Early Miocene), northern Brazil. Boletim do Museu Paraense Emílio Goeldi, Série Ciencias da Terra 1:119-146.

Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012a. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7(2):e31294.

Velez-Juarbe, J., J. I. Noriega, and B. S. Ferrero. 2012b. Fossil Dugongidae (Mammalia, Sirenia) from the Paraná Formation (late Miocene) of Entre Ríos Province, Argentina. Ameghiniana 49:585-593.

Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686-693.

A couple of Friday's ago, we were set to return to the locality where we had been excavating a relatively large whale skull. Last time we were there we manage to make the jacket around the skull, but the plaster did not dry quickly enough, and we had to leave it, as it was late in the day and the tide was coming in. Unfortunately, due to the change in time of the low tide (happening later and later in the day) as well as other technical problems, we could not go back as soon as we wanted. So we ended up waiting a whole week to return and hopefully finish the job.
A local girl, Pedro, Nicole and Samantha pose next to the jacket.To our surprise, the jacket held up during the eight days that passed since we made it. Those were good news as it meant that our work and effort from the previous week was not lost and that we didn't had to make a new jacket. Plaster bandages are hard if not impossible to get here in Panama, so I was extremely happy we didn't had to use more than we already had.
Pedro, a local kid, Erik, Nicole and Samantha happily pose next to the large jacket as we get ready to move it to the truck.We were able to remove the jacket and get it into our truck without further incidents, this wouldn't have been possible without the interns who are doing a great job! To top it off, we even found another tooth associated with the skull. Its not the first one, Aaron had already collected two, which were somewhat incomplete, but hinted at the affinities of the skull. The new tooth we collected is complete, and I can now confidently say that it belongs to a physeterid (a sperm whale)!! Sperm whales are found nowadays in the Caribbean, but their fossil record in the region is relatively poor, with only a handful of reports from a few sites. So this is a fantastic find!One of the teeth associated with the skull in the jacket. Notice the large root and small enameled crown (to the left of the photo).

Stay tuned, as I'm sure we'll keep finding many other interesting fossils here in Panama.

As part of the PCP-PIRE we not only get to look for fossils and study the geology of Panama along the canal. We also get to prospect and collect at other localities. Yesterday, we made the two hour drive to the Caribbean side of the country, where late Miocene marine units are exposed along the beach. If this sounds familiar, is because I had been there a couple of years ago, where, as part of the Pyenson Lab we went to collect a really nice fossil dolphin skull.

On our way to the locality we had to go through the Gatún Lock, and wait for several ships to go through before we could cross.Going to this locality means we have to really plan ahead, as the late Miocene deposits will be best exposed at low tides. That also means that we only have about a four hour window to prospect and collect.
As the water recedes, the rock is exposed and its time to prospect!!Ideally, we can find and collect specimens on a single day (within that 4 hour window), others may take longer, and require to return to the site one or more additional days.

Here Samantha and Pedro work on a project they stated with Aaron several months ago, excavating a large whale skull.We worked two sites simultaneously this day. Pedro, Samantha and Erik continued an excavation they started several months ago with Aaron. They are digging around what seems to be a large whale skull. Nicole and I were about 15-20 meters southwest of where they were. We were busy digging what seems to be part of yet another whale skull. The skull seems to be broken or at least there's a skull and postcranial elements associated with it, so we collected these in two jackets (see picture below).

Here we take a break and have some snacks and talk with the local kids while the two small plaster jackets (center of the pictures) dry out so we can remove them and take them back to the lab.We'll go back today to finish off the large whale skull, and who knows what else we'll find. So stay tuned!

In recent years the efforts to know the fossil terrestrial vertebrates of Panama have been revitalized, in part thanks to the expansion of the canal and the efforts of Panama Canal Project-PIRE in collaboration with the Panama Canal Authority. Vegetation grows fast in the tropics, so good fossiliferous deposits are covered and basically lost within years, even months, of being exposed. The new cuts being made for the expansion of the canal offer a unique opportunity to further understand the geology and paleontology of the area.
Interest in the fossil vertebrates of Panama started when Robert H. Stewart, a geologist with the Panama Canal Company, alongside his assistant, started finding and collecting fossil vertebrate remains in the early 1960's. The fossils were being collected from sediments of the Cucaracha Formation exposed along the Gaillard Cut, one of the artificial valleys that was crucial to the making of the canal. Frank C. Whitmore Jr. (who sadly passes away a little more than a year ago) was then a paleontologist with the US Geological Survey (and expert on fossil mammals) and eventually got involved with the collecting and studying of the Panamanian fossil. He and Stewart published the results of their study in 1965 (Whitmore & Stewart, 1965). Prior to these discoveries, very little was known of the fossil vertebrate fauna of the Central American region, and these were actually the first Miocene fossils found between Honduras and Colombia (Whitmore & Stewart, 1965). Up to that point it was not known wether Central America had been separated from North or South America (some even said both) during the Cenozoic, and if so, for how long? So the discovery of Miocene terrestrial mammals in Panama was a big deal!
The Gaillard Cut and Centenario Bridge in the early morning.One of the main results of Whitmore & Stewart's study was that the Miocene Panamanian fauna was of holarctic* affinities. That meant that at least through the early Miocene, Panama was connected to North America, even though its geographically much closer to northwestern South America**. The fauna studied by them consisted of turtles, crocodylians, horses, rhinos, oreodonts and protoceratids (which I mentioned in a previous post). The mammal assemblage of this fauna is very similar to coeval faunas in North America.
*a term used for the biogeographic region comprising the northern continents.
**we now know that they remained separated by a marine passageway known as the Central American Seaway until about 3 million years ago (Duque-Caro, 1990; Coates et al., 1992).
Another closer look at the Gaillard Cut. Here you can see sediments of the Cucaracha Formation with Centenario Bridge in the Background.The fauna described by Whitmore & Stewart was eventually called the Gaillard Cut Local Fauna (Ferrusquía-Villafranca, 1978; Rich & Rich, 1983; MacFadden, 2006). However, the fossils that make up this fauna had not been described in detail. It wasn't until until Bruce MacFadden of the Florida Museum of Natural History took on the task of describing them, 40 years after they had been collected (MacFadden, 2006). As a result, the composition of the Gaillard Cut Local Fauna has changed due to new discoveries, and will most likely continue to do so in the upcoming years. So, stay tuned as I'll cover this subject on the next post.

*Access to this and all other paleontological localities along the canal brought to you thanks to the courtesy of the Panama Canal Authority (ACP).

References

Coates, A. G., J. B. C. Jackson, L. S. Collins, T. M. Cronin, H. J. Dowsett, L. M. Bybell, P. Jung, and J. A. Obando. 1992. Closure of the Isthmus of Panama: the near-shore marine record of Costa Rica and western Panama. GSA Bulletin 104:814-828.

Duque-Caro, H. 1990. Neogene stratigraphy, paleoceanography and paleobiogeography in northwestern South America and the evolution of the Panama Seaway. Plaeogeography, Palaeoclimatology, Palaeoecology 77:203-234.

Ferrusquía-Villafranca, I. 1978. Distribution of Cenozoic vertebrate faunas in middle America and the problems of migrations between North and South America. Instituto de Geología, Universidad Nacional Autónoma de México 101:193-329.

MacFadden, B. J. 2006. North American Miocene land mammals from Panama. Journal of Vertebrate Paleontology 26:720-734.

Rich, P. V., and T. H. Rich. 1983. The Central American dispersal route: biotic history and paleogeography; pp. 12-34 in D. H. Janzen (ed.), Costa Rican Natural History. University of Chicago Press, Chicago, Illinois.

Whitmore, Jr., F. C., and R. H. Stewart. 1965. Miocene mammals and Central American Seaways. Science 148:180-185.

Just a week and a half ago (March 20-21, 2013) was the 62nd Annual Meeting of the Geological Society Southeastern Section, held in San Juan, Puerto Rico. This two day meeting was a great venue, not only to see some interesting presentations, but was also an opportunity to meet colleagues I had not seen in a while. One of the sessions during the first day was chaired by my friend Alvin Bonilla-Rodríguez of the University of Kansas, and myself. The aim of the session, titled: Multidisciplinary Approaches to Caribbean Stratigraphy and Paleontology, was to find out what our colleagues are up to these days. It was both our first time chairing a session, so we were both a little nervous, but I think it went pretty well. We had a great set of talks as well as poster presentations. Overall it was a fantastic meeting, hat-tip to the organizers for doing such a great job!

The title slide of my GSA talk. 
Of course, going to Puerto Rico for a meeting also meant I would stick around for a few days more.
And so I did. It was time to see my family, but also go to the field and revisit some localities.

Friday after the meeting I returned once again to my favorite early Oligocene locality (see previous posts here, here and here). It hasn't rain a lot in Puerto Rico lately, so the exposure was even better as this locality is exposed along the banks of a river. This gave me the opportunity to spend the morning measuring and describing in detail the main fossiliferous section.
The lowermost marine units was remarkable for the presence of the clam Lucina collazoensis (you can see several of them near the center of the picture). Overall, the sequence consists of alternating terrestrial and shallow marine horizons. It is in one of those marine horizons where I have collected several fossil vertebrates, including side-neck turtles, sirenians and rodents among others.

The main part of the section, you can see the terrestrial (brownish-redish units) and the marine (grayish units).Of course, this wasn't the only day I went to the field. The next day I set out to Ponce, in the southern coast of Puerto Rico, where I will meet with colleagues from the Florida Museum of Natural History, as well as others interested in seeing Oligocene and Miocene marine deposits in that area. It was sort of an unofficial post-meeting field trip.

Our first stop in Ponce, where early Oligocene marine deposits are exposed.Some of the fossils found at this locality. Left, some crinoid stem fragments. Crinoids were once inhabitants of shallow seas, but since the end of the Paleozoic, they are more typical of deeper settings. Right, a shark tooth, probably a carcharhinid. After spending a couple of hours at this locality we were ready to move on to the next outcrop. Unfortunately, my field vehicle would not start, and had to get towed back home.
My field vehicle, acting up...The others, went on (we were on three vehicles), hopefully they found interesting fossils.

I'm back in Panama (it was a very short trip to PR). So stay tuned for upcoming entries on the geology and paleontology of this beautiful country.