Fossil Sirenia of the West Atlantic and Caribbean region. Ix. <i>Metaxytherium albifontanum</i>, sp. nov.

ABSTRACTWe describe a new species of the halitheriine dugongid genus <i>Metaxytherium</i> from the late Oligocene of Florida and South Carolina. The new species is represented by cranial and postcranial material, including parts of the axial and appendicular skeleton. <i>Metaxytherium albifontanum</i>, sp. nov., differs from other species of <i>Metaxytherium</i> by the following unique combination of plesiomorphic and derived characters: posterior end of nasal process of premaxilla broad and flat relative to what is observed in most other members of the genus (somewhat resembling <i>M. subapenninum</i>); ventral extremity of jugal under posterior edge of orbit (character 85[1]) (shared with <i>M. krahuletzi</i>); exoccipitals separated in dorsal midline (character 66[1]) (shared with all other species in the genus, except some <i>M. krahuletzi</i>); and innominate with acetabulum (nearly lost or lost in <i>M. crataegense</i>, <i>M. floridanum</i>, <i>M. serresii</i>). This new species was sympatric with two dugongines, <i>Crenatosiren olseni</i> and <i>Dioplotherium manigaulti</i>. The small tusks and cranial morphology of <i>M. albifontanum</i>, sp. nov., indicate that it was likely a consumer of small seagrasses. Our phylogenetic analysis is consistent with previous ones in placing Hydrodamalinae within a paraphyletic <i>Metaxytherium</i> spp. and placing the <i>Metaxytherium</i> spp. + Hydrodamalinae clade as the sister group to Dugonginae. <i>Metaxytherium albifontanum</i>, sp. nov., is the oldest known member of its genus; this might indicate that the group originated in the West Atlantic and Caribbean region and later dispersed to the Old World Tethys region. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP.