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.

Tuesday, February 25, 2014

¡Muerte Súbita en el Océano!

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].

Monday, January 27, 2014

Los roedores más antiguos del Caribe

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 (en esta localidad), y el otro de las Calizas Lares (de esta localidad; ver foto arriba). Respectivamente, estas formaciones se depositaron durante las épocas geológicas conocidas como Oligoceno temprano y Oligoceno tardío. 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 27-24 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 27 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 (megalonichido) 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 temprano 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. 

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.

Tuesday, January 14, 2014

The oldest Caribbean rodents

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 Rico
It’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 are the localities in Puerto Rico, Río Guatemala (RG), and Lares Limestone (LL). 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.

Wednesday, December 18, 2013

Back to the western Caribbean, Pt. 3

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!

Tuesday, December 3, 2013

Back to the western Caribbean, Pt. 2

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.