Dimetrodon

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Look at that picture to the right. What do you think that guy is? If you're thinking a Dinosaur, you'd actually be wrong. That guy over there is a Dimetrodon, an animal belonging to the genus of the same name that actually predated the Dinosaurs by 40 million years.

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Dimetrodons are actually more closely related to mammals than they are to reptiles. They are synapsids, tetrapods with one hole in the skull located closely behind each eye. Mammals are also synapsids, while animals like birds and reptiles are saurapsids. Synapsids were dominant creatures during the Permain period (299-251 million years ago), and the Dimetrodons in particular were apex predators. The name actually refers to the fact that they have two types of teeth, canines as well as sheering teeth.

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Dimetrodons are perhaps best known for the massive sails on their backs. This sail is actually made from spines that grow directly from the vertebrae. No one really knows for sure what the purpose of these sails was, but one theory is that they helped to regulate temperature. Dimetrodons were also pretty big for tetrapods of their day, with some species growing up to 13ft (4m).

Unfortunately, the Permian period met a disastrous end. Around 251 million years ago the largest mass extinction ever took place, wiping out 90% of all marine life and 70% of all land animals. Dimetrodons did not make it (in fact, they were already gone 30 million years before that-- around 280 million years ago), but some other synapsids did, including our very own distant relatives!