Placerias was a 1 tonne Kanneymerid Dicynodont, (a mammal-like reptile) It was one of the last and largest of its kind, and went extinct in the Late Triassic. They had tusks on their faces, used in defence and for males fighting for mates and territory. As one of the last of its kind, Placerias is a good example of a species at a crossroads in evolutionary history; out with old, in with the new. Not only is Placerias the last of its kind at the end of the Triassic Period,(221-200) it is also the last of its kind at the end of the Upper Palaeozoic Era-Lower Mesozoic Era rule of the 'mammal like reptiles'. After its passing - and even whilst it was still around towards the end - the herbivorous niche that Placerias and its kind had mastered for millions of years, was taken by the newer plant eating Dinosaurs, such as the voracious Prosauropod Plateosaurus. These were far more versatile, and could graze upon Placerias' favoured low lying food, as well as the plants growing on the trees and taller fern related plants that the Placerias simply could not reach (in fact, Plateosaurus could just flatten trees and eat the chosen parts it wanted at leisure. By comparison, Placerias was a limited herbivore)
Placerias featured in the first episode of Walking with Dinosaurs - New Blood. The herd was ambushed by a Postosuchus, which successfully killed one, however it sustained a wound in the process. When it tried to attack again, it was spotted and the Placerias herd warded it off. However, in the end, they are all killed off by the dry season (not the species, but those in this region - this is confirmed in the book to the series, though not shown on-screen)
In the wet season they are seen to act much like hippos, bathing in the water during the hot afternoon.
Placerias weren't seen in any Walking with Dinosaurs specials.