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Prehistoric mammals bulked up to survive in the changing post-dinosaur world © Getty Images

Prehistoric mammals bulked up to survive in the changing post-dinosaur world

Published: 31st March, 2022 at 18:00
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CT-scanning study shows it was brawn, not brains, that allowed our ancestors to outlive the dinosaurs.

In the first 10 million years after the extinction of the dinosaurs, mammals developed bigger bodies to help cope with the radical changes that were occurring on Earth, researchers at the University of Edinburgh have found.


To make the discovery, the team CT-scanned a collection of complete skulls and skeletons of mammals that lived immediately after the mass extinction of dinosaurs discovered in the badlands of north-western New Mexico.

It was previously thought that mammals’ relative brain sizes, the size of their brains in relation to their bodies, increased following the catastrophic asteroid impact that ended the reign of dinosaurs 66 million years ago. The theory being that bigger brains would have allowed the prehistoric mammals to take advantage of any new opportunities that opened up as the dinosaurs died out.

Crania and virtual endocasts inside the translucent cranium of the Paleocene mammal Arctocyon (left) and the Eocene mammal Hyrachyus (right)
Cranium of Arctocyon, a mammal that lived during the Paleocene Ornella Bertrand and Sarah Shelley (left), and Hyrachyus , a mammal that lived during the Eocene 55 to 34 million years ago (right) © Ornella Bertrand and Sarah Shelley

However, the team’s findings show that the relative brain sizes in fact decreased at first due to early mammals’ rapid increase in body size.

Results of scans also suggest the animals relied heavily on their sense of smell, and that their vision and other senses were far less well developed.

“Large brains are expensive to maintain and, if not necessary to acquire resources, would have probably been detrimental for the survival of early placental mammals in the chaos and upheaval after the asteroid impact,” said lead researcher Dr Ornella Bertrand.

It wasn’t until around 10 million years after the extinction of the dinosaurs that early members of modern mammal groups such as primates began to develop larger brains and a more complex range of senses and motor skills.


“The mammals that usurped the dinosaurs were fairly dim-witted, and only millions of years later did many types of mammals develop bigger brains as they were competing with each other to form new ecosystems,” added senior author Professor Steve Brusatte.


Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Science Focus Podcast.


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