Roedores endémicos del Caribe: una mirada cercana a la microestructura de los incisivos

 Esta semana ha salido una nueva publicación en el Journal of Mammalian Evolution donde junto con un nutrido grupo de colegas describimos la microestructura del esmalte de los incisivos de los roedores caviomorfos caribeños (Marivaux et al., 2022). Los lectores habituales de este blog recordarán que el tema de los roedores caribeños es uno que tocamos con cierta frecuencia, desde las diversas entradas sobre los roedores más antiguos de la región (Partes 1, 2 y 3) hasta un resumen de las diversas especies que han existido en Puerto Rico. Para los que quizás no estén tan familiarizados o necesiten un resumen, les daré un poco de contexto el cual también servirá para entender parte de los motivos detrás del nuevo estudio.

Mapa de distribución de especies actuales de jutías (modificado de Fabre et al., 2014). 

Actualmente en las Antillas existe un grupo de roedores endémicos pertenecientes a la subfamilia Capromyinae, coloquialmente conocidos como jutías. Aunque actualmente hay alrededor de 13 especies (ver mapa arriba), en el pasado, particularmente durante el periodo Cuaternario existían muchas más y gozaban de una distribución más amplia (Woods et al., 2001; Fabre et al., 2014; Courcelle et al., 2019). En adición a esto, existía dos grupos adicionales de roedores caviomorfos endémicos, los Heteropsomyinae y los "Heptaxodontidae" o "jutías gigantes" (Woods et al., 2001; MacPhee, 2009; Upham, 2017). Los Capromyinae y Heteropsomyinae son parte de una radiación endémica de "ratas espinosas" antillanas (Echimyidae), que aparecen en la región por primera vez en el Mioceno temprano de Cuba, representados por la especie Zazamys veronicae (MacPhee & Iturralde-Vinent, 1995). Sin embargo, la relación entre las "jutías gigantes" y otros grupos de roedores caviomorfos ha sido un tema de debate por mucho tiempo, resultando en distintas hipótesis sobre cuales son sus parientes actuales más cercanos (ver resumen en MacPhee, 2011).

Para añadirle a el tema de las "jutías gigantes", en 2020 describimos dos especies de roedores del Oligoceno temprano de Puerto Rico, Borikenomys praecursor y una segunda especie, parecida a Borikenomys, pero más grande (Marivaux et al., 2020). Los resultados del análisis filogenético de ese trabajo sugieren un parentesco entre Borikenomys y Elasmodontomys obliquus ambas especies a su vez cerca a la familia Dinomyidae y con Amblyrhiza inundata en una posición más basal, pero todos dentro del grupo conocido como Chinchilloidea. Mientras que los Capromyinae y Heteropsomyinae son parte de la familia Echimyidae en el grupo Octodontoidea. Elasmodontomys y Amblyrhiza son dos de las especies tradicionalmente clasificadas como parte de Heptaxodontidae ("jutías gigantes"). Por lo cual, nuestros resultado sugieren que Borikenomys y algunas de las "jutías gigantes" posiblemente representan una radiación endémica de Chinchilloidea que llegaron a la región a finales del Eoceno, hace unos 33 millones de años atrás. No obstante, el deseo de utilizar todas las fuentes de información morfológicas posibles nos llevó al trabajo que recién publicamos.

Relaciones evolutivas entre los roedores caviomorfos del Caribe. Octodontoidea (color vino) incluye a las jutías (Capromyinae + Heteropsomyinae), mientras que en azul se observa al clado Chinchilloidea, el cual incluye a Borikenomys praecursor y al menos dos de las "jutías gigantes" (Elasmodontomys obliquus y Amblyrhiza inundata). Modificado de Marivaux et al. (2020).

Para tratar de entender mejor las relaciones entre las distintas especies de roedores endémicos caribeños nos dimos la tarea de analizar la microestructura del esmalte de los dientes incisivos de los Capromyinae, Heteropsomyinae, Heptaxodontidae y Borikenomys (Marivaux et al., 2022). Este tipo de análisis requiere que los incisivos se corten longitudinalmente para luego examinar esa superficie utilizando un microscopio electrónico de barrido (scanning electron microscope), para así observar los detalles de la microestructura de la parte interna del esmalte.

Aquí se observa un incisivo cortado longitudinalmente y las zonas y subzonas del esmalte que se examinan en detalle a diferentes aumentos. Tomado de Marivaux et al. (2022).

Para que nuestro trabajo fuera lo más completo posible, utilizamos especímenes de varias colecciones para así tener representantes de la mayor cantidad de especies de roedores caviomorfos caribeños (actuales y extintos) como fuera posible, con un total de 18 especies. Decidimos estudiar la microestructura del esmalte ya que la misma tiene lo que nos referimos como señal filogenética. En otras palabras, la microestructura de los incisivos de roedores tiene una morfología específica y distintiva para cada grupo y nos puede dar una buena idea respecto a qué grupo pertenecen los especímenes que se están examinando. Esta es una herramienta muy útil, especialmente en casos donde se requiere información adicional o cuando solamente encontramos incisivos y no hay otros dientes. Y esto fue el caso en un trabajo previo, del 2014, donde haciendo este tipo de análisis logramos demostrar que los roedores caviomorfos ya estaban en las Antillas para el Oligoceno temprano (aquí hay más detalles sobre ese trabajo). 

Los caviomorfos presentan varios tipos de organización de los cristales de hidroxiapatita que conforman la parte interna del esmalte de los dientes. Los primeros dos tipos se clasifican como Sbt. 1 y Sbt. 2 incluyendo una etapa transicional que se le conoce como Sbt. 1-2. Estos tipos son los más plesiomórficos (o primitivos), mientras que el tercero, Sbt. 3 es el más derivado o avanzado y es el arreglo con mayor resistencia estructural. Entre los roedores caviomorfos los tipos Sbt. 1 y 2 se ven en tres grupos: Erethizontoidea (e.g. coendúes y puercoespines), Cavioidea (e.g. capibaras y agutíes) y Chinchilloidea (e.g. pacaranas y chinchillas); mientras que el Sbt. 3 es exclusivo de los Octodontoidea (e.g. jutías y ratas espinosas). Cada tipo de microestructura de esmalte aparece muy temprano durante la historia evolutiva de cada grupo, prácticamente, cada grupo ya está diferenciado desde el Eoceno-Oligoceno (Martin, 2004, 2005; Boivin et al., 2019).

Los resultados de nuestro estudio muestran que los Capromyinae (e.g. Isolobodon portoricensis y Capromys pilorides) y los Heteropsomyinae (e.g. Boromys torrei), tienen microestructura de esmalte tipo Sbt. 3 (ver figura abajo). Esto es consistente con su clasificación dentro de Octodontoidea y con resultados de otros estudios morfológicos y moleculares.

Detalle de la microestructura de esmalte de varias especies de caviomorfos caribeños, específicamente los Capromyinae Isolobodon portoricensis y Capromys pilorides, y Heteropsomyinae, representado por Boromys torrei. En las imágenes a la derecha se puede apreciar el mayor grado de entrelazamiento de los cristales de hidroxiapatita que forman el esmalte (modificado de Marivaux et al., 2022).

Mientras tanto, en los "Heptaxodontidae" la microestructura del esmalte observada es de los tipos Sbt.1 en Clidomys sp., y Sbt. 1-2 (intermedio) en Elasmodontomys obliquus y Amblyrhiza sp., el cual también ocurre en Borikenomys praecursor (ver figura abajo). Esta morfología, junto con la de sus molares, sugiere que estas especies están emparentadas y pertenecen dentro de Chinchilloidea, lo cual es congruente con el análisis filogenético que publicamos hace unos años (Marivaux et al., 2020). Adicionalmente, Clidomys y Amblyrhiza también comparten características de la región auditiva con otros Chinchilloidea. 

Detalle de la microestructura de esmalte de varias especies de caviomorfos caribeños, específicamente los "Heptaxodontidae" Elasmodontomys obliquus y Amblyrhiza sp., y Borikenomys praecursor. En las imágenes a la derecha se puede observar la organización menos compleja de los cristales de hidroxiapatita que forman el esmalte (modificado de Marivaux et al., 2022).

Sin embargo, estos resultados contrastan con los de un estudio de ADN antiguo (ADNa) donde sugieren que Elasmodontomys es un Capromyinae (Woods et al., 2021), lo cual implicaría que las complejas características dentales compartidas entre Borikenomys, Clidomys, Elasmodontomys y Amblyrhiza evolucionaron convergentemente. Implica además que en Elasmodontomys ocurrió una reversión evolutiva en la microestructura de los incisivos, de tener un antepasado con Sbt. 3 a tener la versión más plesiomórfica y estructuralmente menos estable de Sbt. 1-2. Esto difiere del patrón general que se observa en los Octodontoidea (incluyendo Capromyinae), los cuales presentan microestructura tipo Sbt. 3 desde finales del Eoceno y sería un tipo de reversión evolutiva sin precedente, ya que la presión selectiva es a reenforzar los incisivos, no a debilitarlos.

Otra alternativa a esta discrepancia entre resultados morfológicos y moleculares es que sea el resultado de un error de muestreo en el estudio de Woods et al. (2021). La probabilidad de esto se debe a que los restos de Elasmodontomys se encuentran frecuentemente en la misma localidad que los de Heteropsomys (e.g. McFarlane, 1999; Vélez-Juarbe & Miller, 2007), e incluso Isolobodon (pers. obs.). Partiendo de esto, la mejor forma de resolverlo será extraer ADNa de restos que sin duda sean de Elasmodontomys (e idealmente otras especies de "jutías gigantes"). También hay que concentrar esfuerzos de campo para encontrar fósiles que ayuden a completar el registro fósil de los roedores caviomorfos caribeños. 

Literatura

Courcelle, M., M.-K. Tilak, Y. L. R. Leite, E. J. P. Douzery, and P.-H. Fabre. 2019. Digging for the spiny rat and hutia phylogeny using a gene capture approach, with the description of a new mammal subfamily. Molecular Phylogenetics and Evolution 136:241–253.

Fabre, P.-H., J. T. Vilstrup, M. Raghavan, C. Der Sarkissian, E. Willerslev, E. J. P. Douzery, and L. Orlando. 2014. Rodents of the Caribbean: origin and diversification of hutias unravelled by next-generation museomics. Biology Letters 10:20140266.

MacPhee, R. D. E. 2009. Insulae infortunatae: establishing a chronology for Late Quaternary mammal extinctions in the West Indies. In: Haynes, G. (ed.) American Megafaunal Extinctions at the End of the Pleistocene. Springer, Dordrecht, pp. 169–193.

MacPhee, R. D. E. 2011. Basicranial morphology and relationships of Antillean Heptaxodontidae (Rodentia, Ctenohystrica, Caviomorpha). Bulletin of the American Museum of Natural History 363:1–70.

MacPhee, R. D. E. and M. A. Iturralde-Vinent. 1995. Origin of the Greater Antillean land mammal fauna, 1: new Tertiary fossils from Cuba and Puerto Rico. American Museum Novitates 3141:1–30.

Marivaux, L., L. W. Viñola-López, M. Boivin, L. Da Cunha, P.-H. Fabre, R. Joannes-Boyau, G. Maincent, P. Münch, N. S. Stutz, J. Vélez-Juarbe, and P.-O. Antoine. 2022. Incisor enamel microstructure of West Indian caviomorph hystricognathous rodents (Octodontoidea and Chinchilloidea). Journal of Mammalian Evolution. DOI: 10.1007/s10914-022-09631-7

Marivaux, L., J. Vélez-Juarbe, G. Merzeraud, F. Pujos, L. W. Viñola López, M. Boivin, H. Santos-Mercado, E. J. Cruz, A. Grajales, J. Padilla, K. I. Vélez-Rosado, M. Philippon, J.-L. Léticée, P. Münch, and P.-O. Antoine. 2020. Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies. Proceedings of the Royal Society B 287:20192806.

Martin, T. 2004. Incisor enamel microstructure of South America's earliest rodents: implication for caviomorph origin and diversification. In: Campbell, K. E. (ed.) The Paleogene Mammalian Fauna of Santa Rosa, Amazonian Peru. Natural History Museum of Los Angeles County Science Series 40:131–140.

Martin, T. 2005. Incisor enamel schmelzmuster diversity in South America's oldest rodent fauna and early caviomorph history. Journal of Mammalian Evolution 12:405–417.

McFarlane, D. E. 1999. Late Quaternary fossil mammals and last occurrence dates from caves at Barahona, Puerto Rico. Caribbean Journal of Science 35:238–248.

Upham, N. S. 2017. Past and present of insular Caribbean mammals: understanding Holocene extinctions to inform modern biodiversity conservation. Journal of Mammalogy 98:913–917.

Vélez-Juarbe, J., and T. E. Miller. 2007. First report of a Quaternary crocodylian from a cave deposit in northern Puerto Rico. Caribbean Journal of Science 43:273–277.

Vélez-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., R. Borroto-Páez, and C. W. Kilpatrick. 2001. Insular patterns and radiations of West Indian rodents. In: Woods, C. A., & Sergile, F. E. (eds.) Biogeography of the West Indies: Patterns and Perspectives. CRC Press, Boca Raton, pp. 335–353.

Woods, R., I. Barnes, S. Brace, and S. T. Turvey. 2021. Ancient DNA suggests single colonisation and within-archipelago diversification of Caribbean caviomorph rodents. Molecular Biology and Evolution 38:84–95.

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.

Bad weather, ancient oceans and modern seagrasses… a brief visit to Puerto Rico

Summertime is normally when geologist and paleontologist engage in fieldwork. For me the last two summers have been different; I’ve spent both teaching in the human anatomy lab at USUHS, which has been a fantastic experience. However, being busy in the summer months hasn’t really stopped me from doing a little fieldwork, fortunately, I work mostly in the Caribbean region where the weather is generally nice and the only thing to worry about is hurricane season…

And so it was that I had the chance to go to Puerto Rico at the end of the summer and in the midst of hurricane season. Every time I go there is both for pleasure and work; I get to see my family, enjoy the food and scenery and with a healthy dose of fieldwork, it makes for the perfect vacation. This time I arrived two days before hurricane Irene (then still a tropical storm) hit the island. I was fortunate to be staying in the northwestern part of the island, which did much better than most other parts. We got rain, lots and lots of it, which kind of messed up my plans for fieldwork a little bit.

Meanwhile, while it rained, I stayed busy looking through fossils I had collected during my years as an undergrad; mostly fish teeth (bony and cartilaginous) and otoliths, which I’ll use for some projects on the works. It wasn’t until five six, days after my arrival that it was sunny and dry enough to go out to the field. Without much time to go to different places, I decided that my best chances for fieldwork were in the vicinity of my hometown, basically here and here.

The early Oligocene "mystery" bone I found.

So first I went to the Río G locality where early Oligocene deposits are exposed along the banks of the river. Its one of my favorites and almost always I find something of interest. With all the rain, I was both worried and hopeful. Worried that cool stuff was being eroded away, but hopeful in that new stuff would be exposed. After prospecting for a while and not finding anything more than some sirenian ribs, I made it to the “bonebed” (previously featured here). This time around all that I found was an interesting piece of bone (see picture above), and as it turned out, I had good reasons be worried. If you look at the picture, the part of the bone towards the bottom had broken off, recently, probably during the rain and increased water levels earlier in the week. It doesn’t seem to be a rib, which is why I think its interesting, but due to its incompleteness I’m still not sure what it is… it sounds a bit frustrating, but the best thing to do is to turn that frustration into motivation to keep looking!

 My favorite beach in the Atlantic coast of Puerto Rico. Just how I like it, early in the morning and nearly devoid of people.

My other field excursion was to the beach. Working with marine organisms that thrive in shallow marine environments is always a good excuse for a trip to the beach (specially in the tropics). Staying in my hometown meant that my favorite beach on the Atlantic coast of Puerto Rico was only a 15-minute drive away! I didn’t see any manatee (wasn’t expecting to anyways) but did get to see some seagrass beds (see picture below).

It was wavy and shallow (~1m) hence all the suspended sediment. The turtle grass blades (leaves) are about 0.5-1 cm wide and ~10-12 cm long.

Most seagrass beds in the Western Atlantic and Caribbean region consist of several species, with Thalassia testudinum (turtle grass), Halodule beaudettei (shoal grass), and Syringodium filiforme (manatee grass) as the more common ones. However, the seagrass bed that I was looking at was monospecific (= only one species present). As far as I could tell it consisted solely of turtle grass. Monospecific beds of turtle grass are not uncommon, in fact, Thalassia is what is known as a climax species. That means that it is the dominant species of seagrass; other species (like the ones mentioned above) are only present in small, disturbed patches or at the periphery of the beds. The dominance of turtle grass over other seagrass species and its consequences (like mass die-offs) in historical times has been partly blamed on overkill of large marine herbivores, mainly seacows and green turtles (Jackson et al., 2001). However, this could be slightly different when viewed from a deeper historical perspective. I hope to bring more on this sometime in the upcoming months…

Jackson, J. B. C. et al. 2001 Historical overfishing and the recent collapse of coastal

ecosystem. Science 293, 629-638.

A river runs through an Oligocene sea: parte III

So, keeping up with stuff I’ve collected at the Río G locality (for previous entries about this locality go here and here), I bring you some of the sirenian material that I collected last January. It is not much, but it adds to stuff I’ve collected previously (as you’ll see).

In tropical regions, a lot of times, good outcrops are along riverbanks. Puerto Rico is no exception and that is why the Rio G locality is so good, the exposure is kept “fresh” because of the nearly constant river erosion. Of course the drawback is that fossils are also lost if nobody visits these type of localities at least once a month or after big rainstorms (at least that’s what I used to do).

The picture above shows one such example. I spotted this bone fragment on the wall, very close to water level (a little more than half a meter). And, as you can see in the inset, the surface facing away from the rock looks freshly broken. I did collect the fossil, and unsuccessfully looked for additional fragments nearby.

Above is the picture of the fossil, in dorsal view (anterior towards the top), and the interpretative drawing. As it turns out the fossil was part of a sirenian skull. What was left of the fossil, is the anterior part of the frontals (Fr) and the nasals (N), the supraorbital processes of the frontals are missing. The convex frontal roof and shallow nasal incisure (the concave area between the frontals) are some characters that identify this fossil as belonging to a halitheriine dugongid. In fact, it is very similar to the same part of a much more complete skull that I collected from that locality several years ago (see below).

The figure above shows the more complete skull. A and B show a close-up dorsal view (anterior towards the top) of the area that was preserved in the fragmentary fossil. C is a dorsal view of the skull (anterior to the right) with the outline of the enlarged area in A. As you can see the frontal and its relationship with the nasals look much the same as the fragmentary fossil. It also displays a shallow nasal incisure at the posterior end of the mesorostral fossa (MRF) and convex frontal roof. In the more complete skull the premaxilla (Pmx) partially cover the nasals and the supraorbital processes (SOP) are preserved. (In A and C it is missing the left nasal process of the premaxilla which is loose and needs to be re-attached, but I was able to put it in the drawing).

I’m pretty certain that the fragmentary fossil belongs to the same species as the more complete specimen; it was a pity that part of it was lost previous to it being found. If you’re well acquainted with extinct sirenians, you can probably guess what genus this skull belongs to. So, go ahead and make a guess!

A river runs through an Oligocene sea: part II

This is the first post of the year and, hopefully, more will follow. Anyways, today I bring you a brief overview of fieldwork that I did back in January while I was in Puerto Rico. I had written in a previous occasion about this locality (you can read part I here) and unlike back then, I did find some vertebrate fossils.

The picture above shows one of the most productive outcrops along this locality. As you can see there are about four distinct units. I and III are paleosols (ancient soil horizons) whereas II seems to be shallow marine/brackish and IV shallow marine deposits. Unit II has yielded good fossils in the past, including a sirenian skull and associated axial skeleton, croc teeth, rodent teeth and some nurse shark teeth (gynglymostomatids) (update: you can read about newer discoveries at this site and other nearby ones here, here, here, here, and here). These beds are part of the San Sebastian Formation of early Oligocene age, which in the past have yielded other interesting fossils such as the sirenian Caribosiren turneri (Reinhart, 1959) and the gharial Aktiogavialis puertoricencis (Vélez-Juarbe et al. 2007), among others.

Like I mentioned in the intro, this time around I did find some cool stuff!

In the photo above you can see a closeup of unit II showing some of the fossils as I found them and before I started digging. The red circles are for turtle shell fragments while the green is a sirenian rib. Yes, I know, they are somewhat difficult to see but click on the picture and look carefully, you’ll see them.

The sirenian rib was isolated and easy to collect; it is fairly normal to find isolated sirenian ribs in the San Sebastian Fm and other Oligocene and Miocene localities in Puerto Rico. In contrast, while digging around the turtle shell fragments shown in the picture above, I kept stumbling upon more fragments, until it was apparent that this represented a partially disarticulated turtle shell. Not only that, but there was also an associated left pelvis (shown in the picture below), not bad!!

One of the first posts on this blog was an overview of what's known of the fossil side-neck turtles from Puerto Rico. In it I mentioned that some pelomedusid (a more technical name for side-necks) material from the San Sebastian Fm. had been described by Wood (1972) as an unknown taxon. In fact, Wood (1972) not only described an incomplete shell and plastron but also an associated pelvis. Maybe this material I collected represents additional specimens of that unknown taxon. However, comparison with the description as well as with other turtle fossils from the overlying Lares Limestone will have to wait until after the specimens are prepared (you can get a glimpse of the preparation process here). Below you can see the jackets with the specimens inside.

Preliminarily, I am quite certain that this San Sebastian turtle is a pelomedusoid just by the morphology of the pelvis. Also, there was one other fossil collected that day (is in the jacket in the far left), which was both interesting and frustrating, but I'll leave that for next time!

Recommended Literature

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

Vélez-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.

Wood, R. C. 1972. A fossil pelomedusid turtle from Puerto Rico. Breviora 392:1-13.

This post was updated April 28, 2020

Prep Work: Update

Wow! It’s been a while since I posted something. Working with some of the material collected back in August when I went to Puerto Rico to do fieldwork with my advisor has kept me busy. In addition, I had no computer for a while, just after posting the previous post, my computer’s hard drive died! Luckily, not much was lost.

Back in June I wrote about some prep work I had been doing on a sirenian skull from Puerto Rico. Well I am glad to say that four years after I collected said skull (in 2005), it is nearly done! So, here are some pictures, from the time it was collected until now.

In the picture above (from 2005) I am in the outcrop with my hand next to where the fossil is. This is a Late Oligocene limestone unit from northern Puerto Rico.

Here is a dorsal and right lateral view of how the fossil looked around 2006 (and actually it looked like that for the last 2 years). You might notice that on the top picture there is a bone floating in the matrix next to the braincase, this is the left squamosal, which is disarticulated.

Here is how the fossil looks like now (2009), with most of the matrix gone and the left squamosal removed. Beautiful, don't you think?!

If you know something about sirenians, you might have noticed that this is a dugongine (large tusks [broken, unfortunately], thickened supraorbital process of frontal, etc.). It is actually quite similar to Dioplotherium manigaulti from the Early Miocene of South Carolina and Florida (Cope, 1883; Domning, 1989). Nonetheless, the Puerto Rican skull is older, Late Oligocene, and it also has some primitive characters that sets it apart from D. manigaulti. This skull along with another one from the same locality make up an important part of my thesis. Fortunately, some postcranial material that was collected this summer, from the same outcrop and same unit, is referable to this taxon. This material also displays differences from other known sirenian postcrania. Pretty cool stuff!!

Previous post about sirenians:

Sirenian diversity in the past

De la tierra al agua (English version here)

Domningia and other Indian sirenians

What's wrong with the hands of Steller's sea cow

Cope, E. D. 1883. On a new extinct genus of Sirenia from South Carolina. Proceedings, Academy of Natural Sciences of Philadelphia 1883:52-54.

Domning, D. P. 1989. Fossil Sirenia of the West Atlantic and Caribbean region. II. Dioplotherium manigualti Cope, 1883. Journal of Vertebrate Paleontology 9:415-428.

Sirenian diversity in the past

Its been quiet here for a while as I’ve been busy working on the preparation of two sirenians skull, as well as getting ready for the upcoming field season.

It’s also been a while since I wrote something about sirenians so, here it goes.

Living sirenians can be divided into two families, Trichechidae (manatees) and Dugongidae (dugongs). Most people are probably more familiar with the manatees, after all, there are three species, West Indian, Amazonian and African, whereas there is only one species of dugong. The geographic distribution of extant sirenians is such that there is mostly no overlap between the different species. As the only living herbivorous marine mammals, it might be that by living in separate regions it reduced the chances of competing for the same resources (i.e. seagrasses). But what about in the past, what does the fossil record of sirenian tells us about their paleoecology.

When we look at the fossil record, sirenians were much more speciose, including multispecies communities in some regions (Domning, 2001). Now lets look at one good example.

The Late Oligocene of Florida

The Late Oligocene sirenian fauna of Florida includes at least three species of dugongids*. The dugongines, Crenatosiren olseni and Dioplotherium manigaulti, and the halitheriine Metaxytherium sp. (Domning, 1989, 1997, 2001). (See illustration below).

*The family Dugongidae includes three subfamilies: Dugonginae, Halitheriinae & Hydrodamalinae.

Illustration of known Late Oligocene sirenians from Florida (all at the same scale). Top, Crenatosiren olseni (modified from Domning, 1997); middle, Dioplotherium manigaulti (from Domning, 1989); bottom, Metaxytherium sp. (this last drawing based on a very similar skull from Puerto Rico, tusks not preserved, but presumed to be small as in the Fl specimen). The numbers in the circles are the degrees of rostral deflection. Mandibles absent in the middle and bottom specimens.

These three species, as you can see, differ in size, and to a lesser degree in rostral deflection. Also different from each other is the size of their tusks, increasing in size from Metaxytherium - C. olseni - Dioplotherium manigaulti. Taken as a whole, these differences (specially tusks size) could be indicators of different feeding habits, with small-tusked sirenians feeding of small rhizomes* and large-tusked sirenians feeding on larger ones (Domning, 2001; Domning & Beatty, 2007). Dugongids most likely used their tusks as a tool to dig out the rhizomes, with the most extreme specialization observed in the dugongines, including very large blade-like tusks as well as cranial adaptations that seemed to have help withstand the forces exerted when digging (Domning & Beatty, 2007).

*Rhizomes = the nutrient-rich, underground stems of seagrasses.

Other examples of sirenian multispecies communities are found in the Early Oligocene of Puerto Rico and the Early Miocene of India, among others (more on this sometime in the future). In addition, in the Pacific, sirenians were not the only herbivorous marine mammals. In the northern Pacific region, sirenians seem to have shared their resources with the desmostylians (see picture below), an interesting (and bizarre) group of mammals that lived from the Oligocene to the Miocene and were presumably feeding and spending time in the marine realm (Domning et al., 1986; Inuzuka et al., 1994). Whereas, in the southeastern Pacific, fossils of aquatic sloths (Thalassocnus spp.) have been found in the same formations as sirenians (Muizon & McDonald, 1995; Canto et al., 2008; Muizon & Domning, 1985; Bianucci et al., 2006; Domning & Aguilera, 2008).

Mounted cast of Palaeoparadoxia tabatai taken at the AMNH.

So, why is it so different in modern times, why do we see such a reduced diversity of sirenians and/or lack of any other herbivorous marine mammals? There has been, apparently, little change in the marine seagrass communities since the Eocene, so what happened? The answers for these and other questions could be answered with more fossils and more research. For now, we can certainly say that, like their close relatives, the proboscideans (elephants), sirenians are the last remnants of a once much more diverse group of animals.

References

Bianucci, G., S. Sorbi, M. E. Suárez & W. Landini. 2006. The southernmost sirenian record in the eastern Pacific Ocean, from the Late Miocene of Chile. Comptes Rendus Palevol 5:945-952.

Canto, J., R. Salas-Gismondi, M. Cozzuol & J. Yáñez. 2008. The aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the Late Miocene of north-central Chile: biogeographic and ecological implications. Journal of Vertebrate Paleontology 28(3):918-922.

Domning, D. P. 1989. Fossil Sirenia of the West Atlantic and Caribbean region. II. Dioplotherium manigaulti Cope, 1883. Journal of Vertebrate Paleontology 9:415-428.

Domning, D. P. 1997. Fossil Sirenia of the West Atlantic and Caribbean region. VI. Crenatosiren olseni (Reinhart, 1976). Journal of Vertebrate Paleontology 17:397-412.

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

Domning, D. P. & O. A. Aguilera. 2008. Fossil Sirenia of the West Atlantic and Caribbean region. VIII. Nanosiren garciae, gen. et sp. nov. and Nanosiren sanchezi, sp. nov. Journal of Vertebrate Paleontology 28:479-500.

Domning, D. P. & B. L. Beatty. 2007. Use of tusks in feeding by dugongid sirenians: observations and tests of hypotheses. Anatomical Record 290:523-538.

Domning, D. P., C. E. Ray & M. C. Mckenna. 1986. Two new Oligocene desmostylians and a discussion of Tethytherian systematics. Smithsonian Contributions to Paleobiology 59:1-56.

Inuzuka, N., D. P. Domning & C. E. Ray. 1994. Summary of taxa and morphological adaptations of the Desmostylia. Island Arc 3(4):522-537.

Muizon, C. de & D. P. Domning. 1985. The first records of fossil sirenians in the southeastern Pacific Ocean. Bulletin du Muséum National d’Histoire Naturelle (Paris) (4)7, Sect. C, no. 3:189-213.

Muizon, C. de & H. G. McDonald. 1995. An aquatic sloth from the Pliocene of Perú. Nature 375:224-227.

A day in the field, Tertiary

This time our field area is in northern Puerto Rico. We decided to visits a couple of outcrops of the Late Oligocene Lares Limestone. If the name of the formation sounds familiar you either know about the geology of Puerto Rico or, have read about it on a previous post.

One of these localities (see picture below), I have visited at least since 2000, and up until very recently, we thought that the only formations present there were the Early Oligocene San Sebastián Formation and the overlying Lares Limestone. Now, thanks to new information regarding the stratigraphy of the Tertiary limestones of the north coast of Puerto Rico (Ortega Ariza, 2009), we know that in this locality, overlying the Lares Ls, there are also units of the Montebello Limestone. The age of the Lares Limestone and Montebello Limestone were designated as Late Oligocene – lower Early Miocene and upper Early Miocene, respectively (Seiglie & Moussa, 1984). New data, using strontium isotopes obtained from tubes of the pelecypod Kuphus incrassatus, seems to indicate, instead, that both formations span the Late Oligocene (Johnson et al., 2006; Ramírez et al., 2006; Ortega Ariza, 2009). If this is correct (more samples need to be run, hint, hint!!) I will like this outcrop even more (sorry, can't hide my love for the Oligocene)!!

Here's the one of my favorite outcrops, where the Lares and Montebello limestones are exposed. The arrow points to a sirenian fossil that is yet to be collected.

Of course, what I’ve been mostly searching in these localities are sirenian remains, but like I mentioned on that previous post, other vertebrates have also been collected. Interestingly, the best sirenian remains have been collected from the upper Lares Limestone, with a total (so far) of two skulls, and a set of nine articulated vertebrae (see picture below). There are more fossils but those will be collected in due time. As for the sirenian skulls, well, they are an important part of my thesis work and I will discuss them at some point in the future.

Some articulated sirenian vertebrae, these have already been collected. This is an earlier picture, there were three more vertebrae behind the one labeled Ca1, the ones anterior to L3 were collected earlier.

References

Johnson, C. C., W. R. Ramírez, L. R. Mark, S. Y. Hernandez, E. A. Barrow, M. Hegewald & J. Velez. 2006. Oligocene reef deposits linked to OPD site 999 with strontium isotope stratigraphy. Geological Society of America Abstracts with Program 38:557.

Ortega Ariza, D. L. 2009. Establishing a high resolution sequence stratigraphy and sea-level curve for Tertiary limestones, Puerto Rico. M.S. thesis, University of Puerto Rico, Mayagüez, Puerto Rico, 132 pp.

Ramírez, W. R., C. C. Johnson, M. Martínez, M. C. Torres & V. Ortiz. 2006. Strontium isotope stratigraphy from Kuphus incrassatus, Cenozoic limestones, Puerto Rico. Geological Society of America Abstracts with Program 38:90.

Seiglie, G. A. & M. T. Moussa. 1984. Late Oligocene-Pliocene trangressive-regressive cycles of sedimentation in northwestern Puerto Rico. American Association of Petroleum Geologist Memoir 36:89-95.

Domningia and other Indian sirenians

Over the last 12 years a number of fossil sirenians have been described from Eocene through Miocene deposits from India. This has not stopped as, new taxa are been discovered and described; much of the effort is spearheaded by Sunil Bajpai of the Dept. of Earth Sciences, Indian Institute of Technology and J. G. M. Thewissen of the Dept. of Anatomy and Neurobiology, NEOUCOM (Thewissen Lab). So far all the fossil sirenians from India have been collected from outcrops in the Kachchh District near the western coast of the country; this area is better known for primitive cetaceans such as remingtonocetids (Kumar & Sahni, 1986).

Eocene

The oldest Indian sirenians come from the Middle Eocene Harudi Formation; a total of three species representing two families: Protosiren sp. (Protosirenidae), Eotheroides babiae, Eosiren sp. (Dugongidae, Halitheriinae) (Bajpai et al. 2006). Other species belonging to those genera are found in Eocene deposits in northern Africa (Domning, 1996) indicating a southern Tethyan influence, better referred to as the Indo-African Region of the Tethys Realm (Harzhauser et al. 2002). There should be more on Eocene sirenians from India, sometime this year.

Oligocene

So far only one Oligocene sirenian is known from this region, Bharatisiren indica (Dugongidae, Dugonginae) from the Maniyara Fort Formation of Late Oligocene age (Bajpai et al. 2006). This is the oldest dugongine found in this region, and it is as old as the dugongines, Crenatosiren olseni and Dioplotherium manigualti from the Western Atlantic (Domning, 1989; Domning, 1997) and a new taxon from Puerto Rico. Dugongines are a group that is thought to have evolved in the Western Atlantic and Caribbean Region (Domning, 2001), the occurrence of B. indica seems to point to a latest Eocene or Early Oligocene origin for the group with subsequent trans-Atlantic dispersal to the Indo-African Region. An alternative scenario, is the origin of dugongines in the Mediterranean region of the Tethys Realm with subsequent east and west dispersal, unfortunately no Early or Late Oligocene dugongines are known from this region (the names of the paleobiogeographic areas based on Harzhauser et al. 2002).

Lateral view of the skull of B. indica from Bajpai et al. (2006).

Miocene

During the Early Miocene there seems to have been a radiation of dugongines in this region. With at least two taxa known Bharatisiren kachchhense, Domningia sodhae* from Khari Nadi Formation (Bajpai & Domning, 1997; Thewissen & Bajpai, 2009), and another currently under study, it is an good example of multispecies communities like the ones present in the Western Atlantic and Caribbean Region (Domning, 2001). As you can see in the composite picture below, a notable difference between B. kachchhense and Domningia sodhae is the rostral deflection, which probably reflects different degrees of specializations for bottom feeding (Domning, 2001). They seem to have had similar shape of their tusks, large and more-or-less oval in cross-section, this morphology most likely aided in obtaining large seagrass rhizomes (Domning, 2001; Domning & Beatty, 2007), although probably at different levels due to the differences in rostral deflection. Interestingly, it seems that there were no post-Eocene halitheriines.

*Domningia sodhae was aptly named after Dr. Daryl P. Domning of Howard University, world renowned paleosirenologist, a well deserved recognition.

Lateral view of B. kachchhense (top; from Bajpai & Domning, 1997) and Domningia sodhae (bottom; image reversed, from Thewissen & Bajpai, 2009).

Where are the halitheriines?

So far no post-Eocene halitheriines are known from the Oligocene and Miocene of India, at least two possible explanations come to mind: (1) they were present but no fossils have been found yet, or; (2) they were totally absent. An explanation for the second alternative could be provided by the invertebrate fauna. Based on gastropod fauna it seems that, during the Oligocene, changes in the geological settings in the Tethys Realm led to changes in the ocean currents and what was previously known as the Indo-African Region was subsequently divided into the Mediterranean-Iranian and Western Indian-Eastern African provinces of the Western Tethyan Region (Harzhauser et al. 2002). Subsequently, during the Early Miocene, further fragmentation of the Western Indian-Eastern African Province led to an increase of South-East Asian influence and the formation of the Proto-Western Indian Ocean Province; this separation was further augmented by the closure of the Eastern Mediterranean seaway during the latest Early Miocene (Harzhauser et al. 2002). The progressive isolation of what would become the Proto-Western Indian Ocean Province from a Tethyan influence might have prevented halitheriines from entering the region, especially after the Late Oligocene, leading to specialization and radiation of dugongines in this part of the world.

 References

Bajpai, S. & D. P. Domning. 1997. A new dugongine sirenian from the Early Miocene of India. Journal of Vertebrate Paleontology 17(1):219-228.

Bajpai, S., J. G. M. Thewissen, V. V. Kapur, B. N. Tiwari & A. Sahni. 2006. Eocene and Oligocene sirenians (Mammalia) from Kachchh, India. Journal of Vertebrate Paleontology 26(2):400-410.

Domning, D. P. 1989. Fossil Sirenia of the West Atlantic and Caribbean Region. II. Dioplotherium manigaulti Cope, 1883. Journal of Vertebrate Paleontology 9:415-428.

Domning, D. P. 1996. Bibliography and index of the Sirenia and Desmostylia. Smithsonian Contributions to Paleobiology 80:1-611.

Domning, D. P. 1997. Fossil Sirenia of the West Atlantic and Caribbean Region. VI. Crenatosiren olseni (Reinhart, 1976). Journal of Vertebrate Paleontology 17:397-412.

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

Domning, D. P. & B. L. Beatty. 2007. Use of tusks in feeding by dugongid sirenians: observations and tests of hypotheses. The Anatomical Record 290:523-538.

Harzhauser, M., W. E. Piller & F. F. Steininger. 2002. Circum-Mediterranean Oligo-Miocene biogeographic evolution – the gastropods’ point of view. Palaeogeography, Palaeoclimatology, Palaeoecology 183:103-133.

Kumar, K. & A. Sahni. 1986. Remingtonocetus harudiensis, new combination, a Middle Eocene Archeocete (Mammalia, Cetacea) from western Kutch, India. Journal of Vertebrate Paleontology 6(4):326-349.

Thewissen, J. G. M. & S. Bajpai. 2009. A new Miocene sirenian from Kutch, India. Acta Palaeontologica Polonica 54(1):7-13.

A river runs through an Oligocene sea

The subject of this post is about my second and final day of fieldwork in Puerto Rico. Yes, I only managed to get two days of fieldwork because these were actually some very short vacations and on top of that it was very rainy. Anyways, I already wrote about my first day of fieldwork during which I searched for tetrapods in the Late Oligocene Lares Limestone. Now on my second day I went out to one of my favorite localities, herein referred to as Río G. This locality consists of exposures of the Early Oligocene age San Sebastián Formation along the banks of a river (See the picture below with me as scale and outcrops on each side of the river). The exposures along this river are considered as typical of the basal part of this formation (Monroe, 1980). The lithology of this formation is varied, with some layers representing ancient soils, river channels, deltaic deposits as well as marine units. Of course this is all in a sequence that makes sense with the tectonic history and paleogeography of the region, an interesting subject, which I will not touch at this moment, but might be discussed sometime in the future.

Now, some interesting tetrapods have been recovered from this formation, such as the sirenian Caribosiren turneri, described by Reinhart in 1959. Also from this formation are known pelomedusid turtles, which were previously discussed here. From the Río G locality, one of the more recent discoveries is the skull of the gryposuchine gavialid Aktiogavialis puertoricensis (Velez-Juarbe, et al. 2007). Other tetrapods found here, include sirenians, part of a croc axial skeleton and the oldest-but-crappiest rodent fossil from the Caribbean region. Some of these, like the sirenians are part of my thesis project, whereas the others are still awaiting description or for better material to turn up.

Unfortunately, same as with the prospecting in the Lares Limestone, no new or even useful vertebrate fossils were found in Río G. The most interesting fossil I found was a plant fossil that might be a seed or some sort of fruit (see picture below of the seed/fruit together with a schematic drawing – the fossil measures about 27 mm across). If it actually turns out to be a seed/fruit it would not be the first time that plant “megafossils” are found in the San Sebastián Formation; about 88 taxa of plant macrofossils from this formation were described by Sir Arthur Hollick in the 1920’s (Graham, 1996). I have yet to see Hollick’s (1926, 1928) papers; therefore I still don’t know if my fossil is similar to any of the material he described.

Well, at least since Río G is along a body of water, it turned out a nice place to do some bird watching. I have on previous occasions observed some of the birds along this river, with the difference that now I had a camera with a good zoom allowing me to take some nice pictures. The composite picture below include, clockwise beginning with the upper left: male Molothrus bonariensis (shiny cowbird); Butorides striatus (green-backed heron); Egretta caerulea (little blue heron); Actitis macularia (spotted sandpiper, this one has the winter plumage hence the lack of spots).

An interesting fact about the shiny cowbird is that it is an invasive species from South America, first reported from the Caribbean region during the latter half of the 1800’s (Post & Wiley, 1977a). It is also a brood parasite; in Puerto Rico it parasitizes about 16 different species of birds with a preference for the yellow-shouldered blackbird (Agelaius xanthomus) (Post & Wiley, 1977b; Pérez-Rivera, 1986). These are actually bad news as the yellow-shouldered blackbird is an endemic to the Puerto Rico bank.

On the earlier half of the day, while stalking a green-backed heron (Butorides striatus), I was unwillingly reminded to always keep an eye of where I put my feet. The reason was that while trying to stealthily sneak up to see where the bird was standing, I almost ended up stepping on a couple of fairly large green iguanas (Iguana iguana) (see composite picture below)!

This was actually the first time I have seen green iguanas in the wild in this part of the island. Iguanas are an introduced pest in Puerto Rico therefore their occurrence in this locality took me totally by surprise, although I am aware that they are getting more common around the island, specially in the east and north where it is more humid (I believe they are still not present in the drier southern coast or that they are much less common there). Green iguanas are doing really well in Puerto Rico; the reason might be that once they reach an adult size, nothing, except maybe humans, will eat them. Perhaps another reason for their success is that until several thousand years ago there were Anegada rock iguanas (Cyclura pinguis) in Puerto Rico (Pregill, 1981); are then green iguanas just filling in an empty niche left over by the extinction of the Anegada rock iguana from Puerto Rico? This is unlikely; rock iguanas (Cyclura spp.) are adapted to xeric environments, which, unlike today, were present in northern PR during the Pleistocene (Pregill & Olson 1981). This means that the habitat that was occupied by C. pinguis in northern Puerto Rico, no longer exist there (rock iguanas are not the only xeric-adapted tetrapod to go extinct in northern PR [op. cit.]). All I know is that from now on I will have to keep an eye out for green iguanas while doing fieldwork, at least in northern Puerto Rico.

References

Graham, A. 1996. Paleobotany of Puerto Rico-from Arthur Hollick’s (1928) scientific survey paper to the present. Annals of the New York Academy of Sciences 776: 103-114.

Hollick, A. 1926. Fossil walnuts and lignite from Porto Rico. Journal of the New York Botanical Garden 27:223-227.

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

Monroe, W. H. 1980. Geology of the middle Tertiary formations of Puerto Rico. US Geological Survey Professional Paper 953:1-93.

Pérez-Rivera, R. A. 1986. Parasitism by the shiny cowbird in the interior parts of Puerto Rico. Journal of Field Ornithology 57(2):99-104.

Post, W. & J. Wiley. 1977a. The shiny cowbird in the West Indies. Condor 79:119-121.

Post, W. & J. Wiley. 1977b. Reproductive interactions of the shiny cowbird and the yellow-shouldered blackbird. Condor 79:176-184.

Pregill, G. K. 1981. Late Pleistocene herpetofaunas from Puerto Rico. University of Kansas Museum of Natural History, Miscellaneous Publications 71:1-72.

Pregill, G. K. & S. L. Olson. 1981. Zoogeography of the West Indian vertebrates in relation to Pleistocene climatic cycles. Annual Review of Ecology and Systematics 12:75-98.

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 & 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.