Early Mammals

When the true mammals first appeared in the late Triassic, some 200 million years ago, they were tiny animals that fed on insects and other invertebrates. Until recently we knew little of the first two-thirds of their history, before the late Cretaceous. The only fossils consisted of a few teeth and jaws with a small assortment of other bones.

Megazostrodon

That situation improved in 1966, when a scientist in southern Africa was digging out some dinosaur remains from upper Triassic rocks. Quite by accident he found a tiny skull with typical mammalian teeth. When the piece of rock was later processed in the laboratory, more of the skeleton was uncovered. It was of a shrew-like mammal about 10 centimetres long including its tail. The little fossil was named megazostrodon, and it is important because, at 200 million years old, it is nearly three times as old as the oldest mammalian skeleton known previously.

Megazostrodon

The first insectivores

Megazostrodon was the fore-runner of the group of mammals called the Insectivora, which includes the modern shrews, moles and hedgehogs. As all the primates, including humans, evolved from early Insectivores, megazostrodon is an important distant ancestor of the human species.

What is not known about megazostrodon is whether it produced living young and fed them on milk, or whether it laid eggs. Nor do we know whether megazostrodon had already evolved fur, and if so, how efficient it was at regulating its body temperature.

A present-day shrew