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After the killer asteroid, mammals got bigger before they got smarter

WASHINGTON – In the aftermath of an asteroid impact 66 million years ago that wiped out the dinosaurs, it seems that the brain is more important than the brain for the mammals that managed to survive the disaster. disaster and conquer a changed world.

An analysis of mammal fossils from the Paleocene, which spanned 10 million years after the asteroid wiped out three-quarters of Earth’s species, researchers said Thursday. as their bodies get much larger, their brain size relative to their body mass actually decreases.

These findings contradict the view that it was intelligence that drove mammals – the bit players in the age of dinosaurs – to become the new rulers of the planet after a mass extinction. series at the end of the Cretaceous.

Ornella Bertrand, a postdoctoral researcher in mammalian paleontology at the University of Edinburgh and lead author of the study published in the journal Science, said: ‘The process by which large brains emerged in mammals mammary extinction is much slower than previously thought.

The researchers performed CT scans on the fossils of 28 mammal specimens from the Paleocene period and 96 from the subsequent Eocene, which spanned 56-34 million years ago. They assessed brain size and development of specific brain components. They found that brain development began during the Eocene, along with a shift in the importance of various functions.

“Contrary to our expectations, the mammals that survived the asteroid and outlasted the dinosaurs were rather faint. They didn’t have the intelligence that comes close to that of mammals today – and intelligence A keen intelligence only appeared many millions of years later,” said University of Edinburgh Paleontologists and study co-author Steve Brusatte.

Mammals began to grow larger in body size almost immediately after the mass extinction that wiped out the dinosaurs, except for their avian descendants. Before that, mammals were usually about the size of a shrew. During the Paleocene, some were as big as bears.

“As the non-avian dinosaurs went extinct, an unprecedented opportunity for mammals, they began to colonize ecological niches that were left empty by becoming large,” says Bertrand. more,” said Bertrand.

The researchers learned that the sense of smell – as measured by the development of the brain’s olfactory bulbs – was important for Paleocene mammals as they assumed new ecological roles. During the Eocene, other abilities such as the greater integration of vision, hearing, memory and motor control – tied to neocortical development – became more important for survival. in.

“There is a price to pay to own a large brain. The energy allocated to the brain is 20% of all the energy allocated to the body. So the evolution of the big brain is only possible. occurs when the benefits of having a brain outweigh the costs of maintaining it,” says Bertrand.

The mammals now boast the largest brain in the animal kingdom relative to body size. Their brain development occurs as competition for resources becomes more intense and complex behaviors become critical to the species’ survival, Bertrand said. Several ancient Paleocene lines have disappeared, being replaced by mammals like those living today.

With the disappearance of dinosaur predators and herbivores, mammals began to fulfill these roles during the Paleocene, a time of evolutionary experimentation. The leopard-sized arctocyon was one of the mammals studied, with large fangs, carnivores, and possibly plants. Ectoconus, the Llama-sized herbivore, also studied, had a large body with strong limbs and feet.

The study focused on the placenta, by far the most common mammalian species. Fossils unearthed in recent years in New Mexico, Colorado and France have provided insight into mammal species during the Paleocene period.

“Within 100,000 years of extinction, species richness increased, and mammal species rapidly became morphologically diverse,” says Bertrand. “Some Paleocene species were quite different overall from modern groups, while others were arboreal and may have been ancestors of primates – the latter group also included humans. During the Paleocene, the mammals were doing their own thing.”

Reporting by Will Dunham, Editing by Rosalba O’Brien

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