Friday, March 13, 2015

There are sharks in those hills!

It was late January, when, alongside some of my colleagues from Vertebrate Paleontology, we headed north towards California's Central Valley, leaving behind the heavy traffic and skyscrapers of LA. More specifically, we were heading to Bakersfield to spend part of the weekend excavating at the world-renowned paleontological site of Sharktooth Hill.
Left: shark teeth are abundant in this area, hence the name. Right: the Sharktooth Hill National Natural Landmark, some of the earlier localities are around this hill, like the pits on the middle of the hillside towards the right. These photos were taken in the spring of 2014.
The hills northeast of Bakersfield where Sharktooth Hill is located; this photo was taken earlier this year (my personal favorite time to go there). 
A brief introduction to STH
Ancient marine deposits known as the Round Mountain Silt are exposed throughout the hills northeast of Bakersfield. Within this deposit there is a particularly dense accumulation of bones of (mainly) marine organisms, known as the Sharktooth Hill (STH) Bonebed. Since the early 1900's, many fossils have been discovered and described from this site, including cetaceans, birds, pinnipeds, and turtles (e.g. Kellogg, 1931; Howard, 1966; Mitchell, 1966; Barnes, 1988; Lynch and Parham, 2003). The bonebed is regarded as one of the most densest accumulation of marine organisms, and is one of the densest accumulation of fossil whales, rivaled only by Cerro Ballena in Chile (Pyenson et al., 2009; Pyenson et al., 2014)!
The Sharktooth Hill Bonebed, here we can see some large ribs of a mysticete being cleaned and you can get an idea of the high density of bones. 
This accumulation was deposited in the seafloor between 15.9-15.2 million years ago, and for many years after its discovery, there were a variety of hypotheses as to what caused such a high concentration of bones. It wasn't until 2009, when Nick Pyenson and his colleagues published the results of a very thorough study detailing how it came to be. The major finding was that the bonebed formed during a period of low sediment deposition that lasted about 700 thousand years. Because of the slow sedimentation, the bones of the dead organisms were not buried soon after death and were easily scavenged and scatters throughout the ocean floor, resulting in a mélange of bones. The paper also highlights that the assemblage may not represent a single snapshot ancient ocean life in California, but that researchers have to keep in mind that these organisms died over a period of several hundred thousand years. This makes the STH bonebed different from other dense marine tetrapod assemblages such as Cerro Ballena where the bonebeds were formed over much shorter spans and can be considered as more precise snapshots in time.

The ongoing NHM dig
The Natural History Museum of LA has had a long history of digging at STH, going back more than 50 years, and we probably hold the largest collection of material from that site. Recently, after a long hiatus, we've had the opportunity to start an excavation at a new site in the area*. At this new site the bonebed is close to the surface, which reduces the amount of time we spend removing overburden.
Setting up our quarry. Vanessa (middle) and Sam (far right) prepare the grid that marks our site. Lisa (far left) picks to tools of the trade she'll be using this day.
For now, a lot of what we do during our digs is carefully removing overburden and exposing the bonebed square meter by square meter. It may sound a bit slow, but we do it this way as part of our plan is to eventually be able to reconstruct the bonebed digitally and have a really good record of how the different bones at our excavation were related to each other before removal. So as you may guess, once a square meter(s) of the bonebed are exposed, we make sure we take a lot of photos before removing the fossils from the ground. The work is methodical and can be tedious at some times (i.e. when you're not finding bones) but in the end it is very rewarding.
Vanessa and Sam work on the northeast corner of our quarry. To the left are a bunch of mysticete ribs, and a few vertebrae and skull fragment all jumbled up.
What's next?
Even after so many years of work at the STH Bonebed, there are still mysteries to solve, new species to be described and/or redescribed based on new finding. So, as we continue our dig at STH, stay tuned for more updates as well as upcoming publication on fossils from this amazing and unique deposit!

*Our dig is possible thanks to the generosity of the landowners who are really supportive of our work out there, and also very enthusiastic, often participating in the dig as well; and to people who have donated money to cover for expenses.

References

Barnes, L. G. 1988. A new fossil pinniped (Mammalia: Otariidae) from the middle Miocene Sharktooth Hill Bonebed, California. Contributions in Science 396:1-11.

Howard, H. 1966. Additional avian records from the Miocene of Sharktooth Hill, California. Contributions in Science 114:1-11.

Kellogg, R. 1931. Pelagic mammals from the temblor Formation of the Kern River region, California. Proceedings of the California Academy of Sciences 19:217-397.

Lynch, S. C., and J. F. Parham. 2003. The first report of hard-shelled sea turtles (Cheloniidae sensu lato) from the Miocene of California, including a new species (Euclastes hutchisoni) with unusually plesiomorphic characters. PaleoBios 23:21-35.

Mitchell, E. D. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-46.

Pyenson, N. D., C. S. Gutstein, J. F. Parham, J. P. Le Roux, C. Carreño Chavarría, A. Metallo, V. Rossi, H. Little, A. M. Valenzuela-Toro, J. Velez-Juarbe, C. M. Santelli, D. Rubilar Rogers, M. A. Cozzuol, and M. E. Suárez. 2014. Repeated mass stranding of Miocene marine mammals from the Atacama of Chile point to sudden death at sea. Proceedings of the Royal Society B 281:20133316.

Pyenson, N. D., R. B. Irmis, L. B. Barnes, E. D. Mitchell Jr., S. A. McLeod, and J. H. Lipps. 2009. Origin of a widespread marine bonebed deposited during the middle Miocene Climatic Optimum. Geology 37:519-522.

Tuesday, January 27, 2015

Its the 11th installment of Fossil Sirenia of the West Atlantic and Caribbean Region!

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 (hereherehere 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

Tuesday, October 28, 2014

Por invitación: Catalina Pimiento nos habla de cuando se extinguió el Megalodón

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 años
La 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 científicas
El 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 estudio
Empezamos 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.

Referencias
Pimiento, 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.

Wednesday, September 3, 2014

New paper on fossil plant from the Neotropics

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.

Wednesday, July 9, 2014

Its the 10th installment of Fossil Sirenia of the West Atlantic and Caribbean Region!

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.

Tuesday, June 24, 2014

Time for a brief update!

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!!

Wednesday, March 5, 2014

Florida gets a new species of fossil seacow!

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 Species
One 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.

Paleoecology
Metaxytherium 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.