A new Pan-sirenian from the late Eocene of Romania
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Abstract
Palaeogene sea-grass communities of Tethyan shallow marine ecosystems encompassed a diverse range of animals, including the ancestors of present-day sirenians. The fossil record of this group from the Eocene of Romania is relatively extensive; however, most occurrences consist only of isolated ribs and, less frequently, skull bones, vertebrae, or elements of the appendicular skeleton. Until now, such remains have typically been identified as Sirenia indet. or assigned to the catch-all taxon ‘Halitherium’. Here we describe a three‑dimensional, incomplete skull along with additional cranial and postcranial specimens from the late Eocene (Priabonian, Cluj Limestone Formation) of the Transylvanian Basin, Romania, and assign them to a new species within the stem group Pansirenia. The new taxon, Prototherium transylvanicum n. sp., possesses a dolichocephalic skull with large premaxillary symphysis, elongated nasals, enlarged infraorbital foramen, whereas the ventral extremity of jugal is positioned under the posterior edge of the orbit, but forward of jugal’s postorbital process. In our parsimony analysis P. transylvanicum n. sp. was erected as the sister species of P. ausetanum and positioned crownward of P. veronense on the cladogram, whereas another member of the genus (P. intermedium s.l.) occupies a more crownward position on the stem as the sister taxon of ‘Halitherium’ taulannense. Consistent with previous studies, we confirm that several endocranial features on the inner surfaces of the parietal and supraoccipital, such as the bony falx cerebri, tentorium osseum, and inner occipital protuberance, reported here for the first time in Prototherium, together with the morphology of muscular attachment on the ventral surface of the basioccipital, may carry the phylogenetic signal of, and contribute to, a better understanding of relationships among the pan‑sirenian taxa. The paraphyletic arrangement of Prototherium in the phylogenetic tree, similar to that observed for Eotheroides, indicates that a comprehensive taxonomic revision of the group is warranted.
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