A group of large, herbivore reptiles might have used communal latrines as early as 240 million years ago, research published in Scientific Reports this week suggests. The find represents the first known evidence of megaherbivore communal latrines in non-mammal vertebrates.

Some mammal groups engage in complex defecation behaviours, in which multiple individuals defecate in a single, relatively small area called a communal latrine. These communal latrines have several ecological functions, including communication between individuals and disease prevention. Among megaherbivore animals, the behaviour is thought to be restricted to mammals, and is poorly documented in the fossil record, tending to be restricted to the late Cenozoic.

Lucas Fiorelli and colleagues present evidence for communal latrines that date to the Middle Triassic, around 240 million years ago, from a site in northwestern Argentina. The authors report the discovery of hundreds of pieces of fossilized dung produced by a group of rhino-like, herbivorous mammal ancestors called dicynodonts. These fossil latrines predate the previous record by 220 million years and are the first known for a non-mammal vertebrate. The findings suggest that mammal-type defecation and social behaviours were present in the distant relatives of mammals.