Cynodonts, the ancestors of mammals

Cynodonts, whose name means 'dog teeth', were a lineage of therapsids that appears in the Late Permian about 260 million years ago. Early forms such as Charassognathus and Procynosuchus from South Africa were a few tens of centimetres long, with a long snout, a bony secondary palate that let them breathe while chewing, and teeth divided into incisors, canines and cheek teeth. Later forms such as Thrinaxodon, from the Early Triassic of South Africa and Antarctica, burrowed.

Many cynodonts show steps toward mammal traits: a larger brain, a likely diaphragm for breathing, more upright limbs, and perhaps whiskers and fur, though the evidence for fur is indirect. In a famous find, a Thrinaxodon was found in a burrow with an amphibian that sheltered with it, reported in 2013 by Vincent Fernandez and colleagues. Cynodonts survived the Great Dying and gave rise to mammals in the Late Triassic, about 225 million years ago. Modern mammals, including humans, are surviving cynodonts.