Procynosuchus (Greek: "Before dog crocodile") was a cynodont, a group that was ancestral to mammals. Procynosuchus, specifically, belonged to a group of cynodonts called Procynosuchidae, one of the earliest cynodonts. It lived during the Late Permian. Procynosuchus was unusual in that it was semi-aquatic, like seals or crocodiles of today, whereas most cynodonts, such as Cynognathus, were terrestrial. Procynosuchus swam by wiggling the front and rear ends of its stiff spine, just like a crocodi… (More on Procynosuchus)