|Reconstruction of Steller's sea cow (Hydrodamalis gigas)|
By Emőke Dénes (Natural History Museum in London) (CC BY-SA 2.5)
A recent paper with a "stellar" cast of authors (here) uses molecular data to firmly establish the position of Steller's sea cow within crown Afrotheria; with additional morphological data it also shows shows how the species fits into the fossil record.
Steller's sea cow (Hydrodamalis gigas) belongs with the dugong (Dugong dugon) in Family Dugongidae whereas the three species of manatee belong to Trichechidae. Together they make up the Order Sirenia, which is sister to the elephant Order Proboscidea.
|Endotheliochorial placenta of the Amazonian manatee |
Fetal (fc) and maternal (mc) capillaries are present
The allantoic sac of elephants and manatees has four chambers and we have shown this to be a shared, derived character of the superorder Afrotheria (here).