The Duogonisauridae are the closest relatives of the elasmarians that we know of. They originated in the Eocene, with Protosirenisaurus messelia, which looked much like the desmostylians of HE. This individual species quickly spread out in diversity, with many species being found in Asia. Duogonisaurids were at their apex in the Miocene, with 10 genus and 8 species, grazing their way through the world’s waters, being watched by all sorts of predators, like mosasaurs, sharks and even some gigantic ammonites. However, when the Ice Age came, a lot of them went extinct, due to the colder waters, and these warm-blooded ornithopods were adapted to the warmer parts of the world, like southern China and the Caribbean, where they are found today. However, one species, ancestral Ornithopotamus were better adapted to the cold, thus forming the different species Arcticopotamus. Today, they are a rare group, consisting of only three members.
Ornithopotaminae (The Stubby Hippopod, the Hadwalrus and the Terra Hippopod)Edit
The genus Ornithopotamus is the most famous genus of duogonisaurid, and contains two genera: the widespread stubby hippopod, and the cold-adapted, walrus-like had walrus. The two could not be more different. Ornithopotamus originated in the Oligocene, and didn’t look too different from the stubby hippopod, Ornithopotamus microcheirus. When the Ice Age came, one subspecies managed to become more adapted to the water, thus creating the new species Arcticopotamus borealis, which lives in the Arctic.
The stubby hippopod, Ornithopotamus microcheirus, lives in the Caribbean, much like a dugong of HE. They travel in small groups of four to six to seven, bellowing and splashing in the water, much like a hippopotamus and dugong, hence their name. In the brief summer, the males, at 6.5 meters long, battle each other, with 500 kg of aquatic ornithopod bashing against each other’s sides. Whoever backs down last gets the smaller females of the harem, who are 4.5 meters long, making the stubby hippopods the second smallest member of their group. However, that does mean that they can gather in smaller places than their larger, more vulnerable relatives.
A more bizarre relative of the stubby hippopod, the hadwalrus seems more likely to be a different taxon rather than a different subspecies of Ornithopotamus. It is recently been discovered to be a different genus of duogonisaurid, thus being renamed Arcticopotamus, as it resembles a cold- and water-adapted Duogonisaurid, and its new name means "arctic hippopotamus". The change of genus name, due to anatomical studies, was efficient. However, not much is known about its behaviour and life style, so it is presumed to behave like a seal of HE.
Another subspecies of Ornithopotamus, the terra hippopod, Ornithopotamus asiaticus, is the most primitive member of the group, and is like the pygmy hippopotamus of HE, except the terra hippopod dwells near the Ganges River, and not the Congo, like its real life counterpart. Like the hadwalrus, terra hippo pods are not known well in terms of behavioural witnesses and eyewitnesses. They are reported, however, to be about 2.5 meters long and are thus far the smallest knownmember of the group. However, if it were in HE, it would be a big impact to the ecosystem that surrounds the Ganges River.