Eozostrodon (Greek for "early girdle tooth"); pronounced EE-oh-ZO-struh-don
Woodlands of Western Europe
Late Triassic-Early Jurassic (210-190 million years ago)
Size and Weight:
About 5 inches long and a few ounces
Long, sleek body; short legs
If Eozostrodon was a true Mesozoic mammal--and that's still a matter of some debate--then it was one of the earliest to have evolved from the therapsids ("mammal-like reptiles") of the earlier Triassic period. This tiny beast was distinguished by its complex, three-cusped molars, its relatively large eyes (which indicate that it may have hunted at night) and its weasel-like body; like all early mammals, it probably lived high up in trees, so as not to get squashed by the larger dinosaurs of its European habitat. It's still unclear whether Eozostrodon laid eggs and suckled its young when they hatched, like a modern platypus, or gave birth to live babies.