The Steller's sea cow (Hydrodamalis gigas) was hunted to extinction by 1768, while the genus Dusisiren is known from fossils dating from the middle Miocene to early Pliocene.
The Steller's sea cow, an ancient marine mammal, met its demise in 1768. Conversely, the genus Dusisiren, which inhabited the Earth during the Miocene and Pliocene periods, is known from fossil evidence.