Steller's sea cow
The sea cow's spine is believed to have had seven cervical (neck), 17 thoracic, three lumbar, and 34 caudal (tail) vertebrae. Its ribs were large, with five of 17 pairs making contact with the sternum; it had no clavicles. As in all sirenians, the scapula of Steller's sea cow was fan-shaped, being larger on the posterior side and narrower towards the neck. The anterior border of the scapula was nearly straight, whereas those of modern sirenians are curved. Like other sirenians, the bones of Steller's sea cow were pachyosteosclerotic, meaning they were both bulky (pachyostotic) and dense (osteosclerotic). In all collected skeletons of the sea cow, the manus is missing; since "Dusisiren"—the sister taxon of "Hydrodamalis"—had reduced phalanges (finger bones), Steller's sea cow possibly did not have a manus at all.