Umoonasaurus demoscyllus was a small short-necked plesiosaur, about 2m long (6’6″), that lived in the polar shallow seas covering much of what is now Australia 115 million years ago during the Early Cretaceous.
Its known fossil remains include a specimen nicknamed “Eric”, one of the most complete opalized vertebrate skeletons ever found.
While most of its body was fairly generalized for a plesiosaur, its skull was unusually ornamented. A raised ridge along the middle of its snout shows evidence of supporting a larger keratinous crest, and smaller ridges over each of its eyes may have also had similar structures. These crests were fairly delicate so were probably mainly used for visual display, and might have been brightly colored.
Tsaidamotherium hedini was a ruminant ungulate living around 11 million years ago during the late Miocene, in the northeastern part of the Tibetan Plateau in what is now Northwestern China. Although it’s known only from partial skull remains it was probably similar in body size to a large sheep, about 80cm tall at the shoulder (2’7″).
Since its discovery in the 1930s it’s traditionally been classified as part of the muskox lineage, but in 2022 it was proposed to actually be a giraffoid very closely related to the newly-discovered Discokeryx.
Tsaidamotherium had some extremely unusual headgear, with highly asymmetrical “horns” (actually ossicones if was a giraffoid). The left one was small and positioned above the eye, while the right one was shifted back and towards the middle of the forehead, and was expanded out into a wide bony disk that would have supported a large helmet-like domed keratin covering.
Its skull also had a very large nasal cavity resembling that of the modern saiga antelope, suggesting it may have convergently evolved a similar sort of complex air-filtering snout to deal with dry cold air in its mountainous habitat.
Champsosaurus might look a lot like an unarmored crocodilian, but it was actually only very distantly related to them – this animal was part of a completely extinct reptile lineage known as choristoderes, and its very gharial-like appearance was the result of convergent evolution.
Found in freshwater habitats across North America and Europe, several different species of Champsosaurus are known from around the middle of the Late Cretaceous through to the end of the Paleocene, surviving through the devasting K-Pg mass extinction 66 million years ago.
Champsosaurus laramiensis here lived in western North America and ranged right across the time of the extinction event, dating to between about 70 and 62 million years ago. Around 1.5m long (~5′), it had a flattened skull that was very wide at the back, supporting powerful jaw muscles, with a long narrow toothy snout that could sweep rapidly through the water to snap at fish in a similar manner to modern gharials. Its nostrils were right at the tip of its snout, and it may have used it like a snorkel, only sticking the very end out of the water to breathe.
Skin impressions show it was covered in numerous tiny scales, most less than 0.5mm in size (0.01″), which wouldn’t have been particularly visible from a distance.
There also seems to have been some sexual dimorphism in this species, with females having much more well-developed limb bones – allowing them to occasionally haul themselves out onto the shore to lay eggs, while males were probably fully aquatic and unable to support themselves on land.
Despite looking more like some sort of scaly tubeworm, Rhenopyrgus viviani here was actually an echinoderm, distantly related to modern starfish, brittle stars, sea urchins, crinoids, and sea cucumbers.
It was part of an extinct Paleozoic echinoderm lineage known as edrioasteroids, which lived attached to the seabed or on hard surfaces like the shells of other marine animals, using the tube feet on their five arms to catch food particles from the water around them.
Living during the Silurian, about 435 million years ago, in what is now Quebec, Canada, it stood around 3-4cm tall (1.2-1.6″), firmly anchored into the seafloor sediment by a bulbous sac-shaped base. Its long stalked body was somewhat flexible, and it was able to partially contract the top feeding region down under a “collar” of large scale-like armor plates.