Placerias was a dicynodont

Dicynodont

Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...

 (a group of mammal-like reptiles) that lived during the late Carnian age

Carnian

The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...

 of the Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 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 metres (11.5 ft) long and weighing up to a ton (907 kilograms).