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Being half reptile and half mammal the cynodonts represent the missing link between these two groups. The cynodont and Placerias were distant relatives but the cynodont was more mammal-like

222 to 215 million years ago Late Triassic period

Name: Pronunciation: Meaning:

Animal Type: Dietary Type: Size: Weight: Major Fossil Finds:

Cynodont Si-NO-dont Dog-toothed Half mammal, half reptile Omnivore - reptiles, eggs, roots, bugs Up to 1 - 1.5 metres Up to 20 kg Petrified Forest Arizona, USA

Evidence The term "cynodont" refers to a broad group of extinct mammal-like reptiles, the Cynodontia. These include the direct ancestors of mammals. In the Petrified Forest, Arizona area only two molar teeth of a large cynodont have ever been found. This animal has been modelled on fossils of another cynodont found in South Africa called Thrinaxodon (thrin-AX-oh-don).

Thrinaxodon lived a little earlier and was about the size of a cat. The teeth from the Petrified Forest were similar to Thrinaxodon's but suggested a much larger animal. Thrinaxodon's teeth were varied with canines, incisors and molars which are mammalian features. Small holes in the bone of the snout suggest whiskers. The presence of whiskers implies body hair and suggests cynodont was warm blooded.