Night Journeys

First Mammals

225 MYA

Small and nocturnal, the first mammals jump, climb, swing and swim through the dinosaur world. Obliged to inhabit small niches in a world of giants, mammals will discover that their diminutive size opens a proverbial window of opportunity.

In the first waves of mammal diversification, some rodent-sized insect-eaters evolve lactation, enabling mothers to spend more time in the nest keeping their young both fed and warm. Some mammal species evolve even smaller bodies.

These insect-eating mammals, among the oldest known, grew to about 4 inches (10 cm) in length. (Illustration by Zdenek Burian, © Jiri Hochman and Martin Hochman)

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