Perplexisaurus

If there’s any equivalent to carcinization in mammals, it’s turning into an otter-beaver-like semi-aquatic form.

Because it just keeps happening.

Modern examples alone include otters, beavers, muskrats, giant otter shrews, desmans, aquatic genets, yapoks, lutrine opossums, and platypuses – and in the fossil record there were early pinnipeds, remingtonocetids, pantolestids, stagodontids, and Liaoconodon going as far back as the early Cretaceous. Even outside of the true mammals there were also Castorocauda, Haldanodon, and Kayentatherium during the Jurassic, and much further back in the late Permian there was the early cynodont Procynosuchus.

So a non-cynodont synapsid doing the exact same thing really isn’t all that surprising.

Perplexisaurus foveatus was a member of the therocephalians, a group of synapsids that were close evolutionary “cousins” of the cynodonts-and-true-mammals lineage. Similar in size to a modern rat, about 20cm long (8″), it lived in Western Russia during the Late Permian about 268-265 million years ago.

At the time this region was a river plain with a tropical climate, experiencing seasonal floods that turned the whole area into what’s known as “viesses” (a name based on the abbreviation “V.S.S.” standing for “very shallow sea”), vast shallow lake-seas that persisted for weeks or months at a time.

So this little animal has been interpreted as being semi-aquatic, swimming around and feeding on aquatic invertebrates and tiny fish and amphibians. Its skull had numerous pits around the front of its face, suggesting that it had a highly sensitive snout – probably whiskery, allowing it to hunt entirely by touch in dark murky water, but it’s also been proposed to have possibly had an electroreceptive sense similar to modern platypuses.

Brontornis

Brontornis burmeisteri was one of the largest flightless birds known to have ever existed, standing around 2.8m tall (9’2″) and estimated to have weighed 400kg (~880lbs).

Known from the early and mid-Miocene of Argentina, between about 17 and 11 million years ago, it’s traditionally considered to be one of the carnivorous terror birds that dominated predatory roles in South American ecosystems during the long Cenozoic isolation of the continent.

But Brontornis might not actually have been a terror bird at all – it may have instead been a giant cousin of ducks and geese.

The known fossil material is fragmentary enough that it’s still hard to tell for certain, but there’s some evidence that links it to the gastornithiformes, a group of huge herbivorous birds related to modern waterfowl.

If it was a gastornithiform, that would mean it represents a previously completely unknown lineage of South American giant flightless galloanserans. And, along with the gastornithids and the mihirungs, it would represent a third time that group of birds convergently evolved this sort of body plan and ecological role on entirely different continents during the Cenozoic.