dimetrodon

noun

1. an extinct carnivorous mammallike reptile, of the genus Dimetrodon, dominant in North America during the Permian Period, up to 10 feet (3.1 meter) long and usually bearing spinal sails.

1. An extinct, carnivorous reptile of the genus Dimetrodon of the Permian Period having a body similar to an alligator’s but with a tall, curved sail on its back. The sail had a thick network of blood vessels and may have been used to regulate the animal’s body temperature. The dimetrodon belonged to the synapsids, an early group of reptiles that was ancestral to mammals.