JOHN SIBBICK / SCIENCE PHOTO LIBRARY JOHN SIBBICK / SCIENCE PHOTO LIBRARY
Estemmenosuchus therapsids drinking water on a shoreline, illustration. Estemmenosuchus existed around 267 million years ago, during the Middle Permian. It was an omnivorous animal, with distinctive horn-like structures. Therapsids included the animals that later evolved into mammals.
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