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Morganucodon, a close relative of Eozostrodon (Wikimedia Commons)


Eozostrodon (Greek for "early girdle tooth"); pronounced EE-oh-ZO-struh-don


Woodlands of Western Europe

Historical Period:

Late Triassic-Early Jurassic (210-190 million years ago)

Size and Weight:

About 5 inches long and a few ounces



Distinguishing Characteristics:

Long, sleek body; short legs


About Eozostrodon:

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.

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