Mammals are very ancient beasts. The earliest known members of our fuzzy family date back to about 225 million years ago, a time when dinosaurs themselves were newcomers on the evolutionary stage in the Triassic.
Naturally, through the fossil record, we know that the “terrible lizards” soon went on to thrive on every continent in every shape and size — and are still with us as birds.
The Dawn of Early Mammals
Mammals, on the other hand, are often treated as evolutionary underdogs during this vast span of time. The mammals of the Triassic, Jurassic, and Cretaceous, the stereotype goes, were small, insect-hunting creatures that tried to evade dinosaurs in the dark. That classic image is all wrong.
Mammals did not attain the same range of sizes as dinosaurs during the Mesozoic; but size isn’t everything. “Mammals still exploited a whole range of ways of living and feeding,” says University of Bristol paleontologist Pamela Gill. This included swimming in water and gliding from tree to tree.
