High Quality Content by WIKIPEDIA articles! The Pantodonta are an order (or, according to some, a suborder) of now extinct placental mammals. Pantodonts are well known from the Paleocene of North America and Asia, and one early genus Alcidedorbignya, that was found in the Paleocene of South America. Pantodonts started out cat-sized in the early Paleocene, but by early Eocene, they had become cow-sized herbivores, the largest land mammals of their time. Then they abruptly died out by the middle Eocene.