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• Evolutionary Essentials
 Mammals Emerge
Mammals evolved from tetrapods that survived the third mass extinction, during the Permian Period.
The first mammals appeared around 210 million years ago towards the end of the Triassic Period during the Mesozoic Era. They evolved from a group of early tetrapods (four-limbed vertebrates) called synapsids. Synapsids bounced back from the mass extinction at the end of the Permian Period more quickly than did reptiles or other tetrapods.
Hair and other mammal characteristics evolved slowly.
Early synapsids looked a little like reptiles, their close relatives. But as new types of synapsids evolved, they became less and less reptile-like, developing mammal-like features such as hair. Eventually, the first true mammals appeared among them.
 Scientists distinguish mammal fossils by their teeth and jawbones.
We all know that mammals have hair, are warm-blooded, and produce milk to feed their young. But these features don’t show up in fossils. Instead, scientists look for features common only to mammal bones, such as their unique teeth and jawbones.
The study of the evolutionary history of mammals and other organisms is called “phylogeny.”
By looking at features that organisms share, scientists can tell how closely related the organisms are. Knowing these relationships, we can trace evolutionary history—phylogeny—and figure out where mammals came from.
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To learn more about the study of mammal evolutionary history, take a look at the Phylogeny video. To access this feature, you will need the Window Media Player plug in for your browser. |
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