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.

6 comments:

Brian Lee Beatty said...

I'm really happy to see this come out, Jorge! You've done a terrific job of it, and I'm sure there are many other sirenians waiting for you for years to come.
Cheers,
Brian Beatty

J. Velez-Juarbe said...

Me too Brian!! Thanks and stay tuned as indeed more stuff will be coming out!!

Jordi Balaguer Bruguera said...

Felicidades, Jorge, por el nuevo artículo. A ver cuando puedo conseguirlo. Por cierto, en el blog ya hablaste de su cráneo hace algún tiempo, antes de describirla, ¿verdad?

Y una cosa que me tiene intrigado: el elevado número de especies y el grado de distribución del género. Lo más habitual en sirenios són géneros con 2 o 3 especies, poco más. Y en cambio Metaxytherium parece haberse diversificado mucho y también repartido mucho por el globo...

JORDI B B said...

Felicidades, a ver cuando puedo leer el artículo. Muchas horas de trabajo acumulado y ahora dando frutos. Por cierto, hace algunos meses ya habías colgado algo referido al cráneo, aún sin "nombre", ¿verdad?

Por cierto, hay algo que me tiene un poco intrigado: la variedad (8 especies) y el rango geográfico del género. Es algo poco habitual en sirenios, generalmente con pocas especies por género(2 o 3; raramente más o a menudo géneros monoespecíficos) o distribución más limitada.

Parece ser un género con buenas capacidades colonizadoras y adaptativas, se diversifica y se distribuye por el globo entre finales del Oligoceno y principios del Plioceno. Muy llamativo...

J. Velez-Juarbe said...

Saludos Jordi y muchas gracias!!
Estas en lo cierto, esta especie ya la había mencionado por acá :)

Si, como dices, usualmente en los sirenios tienes pocas especies dentro de un género, y en general los géneros son de duración corta. Metaxytherium es inusual, tiene alto número de especies, amplia distribución geográfica y rondó por lo océanos por mucho tiempo, del Oligoceno tardío al Plioceno temprano.

J. Velez-Juarbe said...

Pues creo que parte del éxito de este género es como mencionas, su buena capacidad adaptativa. No más ver el formidable ejemplo del Mediterráneo. Donde primero reducen su tamaño (camino a la crisis del Mesiniano) y luego volviéndose más grande y con mejores herramientas (incisores más grandes) para socavar los pastos marinos.