Herein, we describe a new early Miocene dugongine from marine deposits of the Culebra Cut (Gaillard Cut) of the Panama Canal. The new taxon, Culebratherium alemani, gen. et sp. nov., represents one of the few records of late Aquitanian–early Burdigalian sirenians and the oldest sirenian from Central America. A phylogenetic analysis places Culebratherium in a clade with Dioplotherium cf. D. allisoni (Miocene of Brazil), Dioplotherium allisoni (Miocene of Baja California Sur, Mexico, and California, U.S.A.), and Dioplotherium sp. (Pliocene of Yucatan, Mexico). Similar to these taxa, Culebratherium is characterized by the presence of large incisor tusks, a premaxillary symphysis without a boss, a premaxilla-frontal suture forming a butt joint, and a moderately downturned rostrum. In addition, Culebratherium exhibits prominent occipital-cervical attachment sites for enlarged neck musculature. These features taken together are interpreted as adaptations for uprooting large, deeply buried seagrass rhizomes. Other dugongines with similar, yet convergent, dental and facial adaptations are known from earlier or coeval deposits in Puerto Rico, Florida, South Carolina, California, Baja California Sur, Brazil, and India and were constituents of sympatric paleocommunities of sirenians. Only fragmentary evidence of a second smaller and unidentifiable sirenian species is known from the Culebra Formation, but future discoveries may reveal a similar sympatric paleocommunity during the early Miocene of Panama. Finally, we used the results of the phylogenetic analysis to propose the new clade Pan-Sirenia as the most inclusive group consisting of stem and crown groups and redefine the Sirenia, Dugongidae, and Dugonginae clades.