Fossil range: Late Triassic
A herd of Placerias hesternus
| Scientific classification
Placerias was a dicynodont (a group of mammal-like reptiles) that lived during the late Carnian age of the Triassic Period (221-210 million years ago). It was a member of the family Kannemeyeridae, the last known representative of the group at this time: the dicynodonts went extinct shortly afterwards.
This animal was the biggest herbivore of its time, measuring up to 3.5 meters (11.3 feet) long and weighing up to two tons (907 kilograms). Placerias had a powerful neck, strong legs, and a barrel-shaped body. There are possible ecological and evolutionary parallels with the modern hippopotamus, spending much of its time during the wet season wallowing in the water, chewing at bankside vegetation. Remaining in the water would also have given Placerias some protection against land-based predators such as Postosuchus. Placerias used its beak to slice through thick branches and roots with two short tusks that could be used for defence and for intra-specific display.
Fossils of forty Placerias were found near St. Johns, southeast of the Petrified Forest National Park in Arizona. This site has become known as the 'Placerias Quarry' and was discovered in 1930, by Charles Camp and Samuel Welles, of the University of California, Berkeley. Sedimentological features of the site indicate a low-energy depositional environment, possibly flood-plain or overbank. Bones are associated mostly with mudstones and a layer that contains numerous carbonate nodules.
In popular cultureEdit
To date, Placerias has appeared in one television documentary, Walking with Dinosaurs. They were shown living in riverbeds, much like the modern hippo. In another scene, they are shown migrating to find new food.
- Haines, Tim, and Paul Chambers. The Complete Guide to Prehistoric Life. Pg. 68. Canada: Firefly Books Ltd., 2006.