Sirenia (Sea Cows/Dugongs and Manatees)
Family: Dugongidae (Dugongs or Sea Cows)
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Status | Taxon Profile |
| Hydrodamalis gigas | Zimmermann, 1780 | Steller's sea cow | 1768 | Bering Island, Commander Islands (= Kommandorskiye Islands), Russia | Extinct | Access |
Family: Trichechidae (Manatees)
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Status | Taxon Profile |
|
Trichechus hesperamazonicus
|
Perini et al., 2020 | Late Pleistocene | Rondônia, Brazil (western) | Extinct | Access | |
| Trichechus manatus bakerorum | Domning, 2005 | - | Late Pleistocene | North America | Extinct | Access |