Ok, so while I slowly prepare a more lengthy post. Here’s the answer from last post. The skull I showed last time is that of a species of Metaxytherium, exactly which one, well, I’ll talk about that in the future. That skull is from Early Oligocene deposits, therefore it is several million years older than other reported species of Metaxytherium.
Here’s the skull in lateral and dorsal views. (Notice that part of the rostrum is missing.)
It is somewhat similar to M. crataegense (=M. calvertense [Aranda-Manteca et al., 1994]) from the Early Miocene of the Western Atlantic and Caribbean, as well as to other species of Metaxytherium, but, it also displays plesiomorphic conditions not seen in those other species. 
Another possibility would be Caribosiren turneri (drawing above modified from Reinhart, 1959), from the Early Oligocene of Puerto Rico. But, unlike Caribosiren the rostrum of this critter doesn’t seem to have been as extremely downturned; also it belonged to an animal at least 15% larger than Caribosiren. Other Oligocene halitheriines such as Halitherium schinzii from the European Early Oligocene, have different morphology of the parietal as well as much larger nasals; Eosiren imenti, known from the Early Oligocene of Egypt (Domning et al., 1994), is even more primitive than Halitherium schinzii, as it still has permanents premolars and canines, among other characteristics.
So, as far as I can tell, it seems to be a primitive Metaxytherium. There are other skulls from Early or Late Oligocene of the western Atlantic, which are very similar to this one, possibly the same species, that’s one thing I have to figure out as part of my thesis. If you’re going to the SVP meeting this year, you might learn more about this critter.
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.
Domning, D. P., P. D. Gingerich, E. L. Simons and F. A. Ankel-Simons. 1994. A new Early Oligocene dugongid (Mammalia, Sirenia) from Fayum Province, Egypt. Contributions from the Museum of Paleontology, the University of Michigan 29(4):89-108.
Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.
Ciertamente interesante, la pieza. Aunque la asignación a Metaxytherium es sorprendente, teniendo en cuenta la datación, ya que este género se asocia sobretodo al Mioceno. De todas maneras, ¿que posibilidaes hay que pueda ser algo parecido a la conexión entre Halitherium y algunos géneros típìcamente caribeños?
ReplyDeleteSaludos Jordi,
ReplyDeleteGracias por tu comentario, muy buena pregunta! Lo interesante de este espécimen, es que es más parecido a Metaxytherium que a cualquier otro género dentro de los Halitheriinae del Oligoceno (Eosiren, Halitherium ó Caribosiren) y no es lo suficientemente diferente para merecer un nuevo género; de hecho, es muy parecido a M. crataegense del Mioceno temprano del Atlántico occidental y Caribe.
Puede que exista una conexión entre Halitherium schinzii ya que es el taxon hermano de Caribosiren y los Metaxytherium spp. Sin embargo, yo tengo la sospecha que Halitherium nunca estuvo presente en el Caribe y Atlántico occidental, los fósiles de esa región asignados a ese género son muy incompletos, y sospecho que representan algo diferente dentro de Halitheriinae. Esta subfamilia aparece por primera vez en América del Norte durante el Eoceno medio, existe un cráneo (que están describiendo) que tiene afinidades con los Halitheriinae de la costa sur del Tethys (algo como Eotheroides). Es posible que de algo derivado de ese espécimen, haya surgido los otros Halitheriinae caribeños.