Mammals grew big after dinosaurs died but their brains stayed small

After the extinction of the dinosaurs, mammals took over and had room to evolve larger bodies, but their brains remained small to begin with

Life 31 March 2022

Ancient mammal skulls

A reconstruction of the brains (purple) inside the skulls of the mammals Arctocyon primaevus (left), which lived about 59 million years ago, and Hyrachyus modestus (right), which lived about 45 million years ago

Ornella Bertrand and Sarah Shelley

In the wake of the mass extinction 66 million years ago that wiped out all of the dinosaurs apart from the birds, mammals underwent an evolutionary explosion. The small species that survived the consequences of the asteroid-triggered “end-Cretaceous” event diversified and began to evolve into new niches, filling forests that sprung up from the ashes of the …

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