Researchers on Thursday said an analysis of mammalian fossils dating back to the Old Age – which spans 10 million years after the asteroid disappeared three-quarters of the Earth’s species – found that while their bodies became much larger, their brain size relative to with body mass decreased. .
The findings contradict the notion that it was the intelligence that led the mammals – dinosaur bite players – to become the new rulers of the planet after their mass extinction at the end of the Cretaceous.
“The process of developing large brains in mammals after extinction has been much slower than previously thought,” said Ornella Bertrand, a postdoctoral researcher in mammalian paleontology at the University of Edinburgh and lead author of the study, published in the journal Science.
The researchers performed computed tomography scans of 28 Paleocene mammals and 96 of the following Eocene, which spanned 56-34 million years ago. They evaluated the size of the brain and the development of specific brain components. The development of the brain, they found, began during the Eocene, along with a change in the importance of the various functions.
“Contrary to our expectations, mammals that survived the asteroid and overtook the dinosaurs were quite noisy. They had almost no brain power of modern mammals – and the intense intelligence came only millions of years later,” said the University of Paleontology. of Edinburgh and co-author of the study Steve Brusatte said.
Mammals began to gain larger body size almost immediately after the mass extinction that wiped out the dinosaurs, in addition to the offspring of their birds. Before that, mammals were usually about the size of an old woman. During the Paleocene, some became as big as bears.
“When non-bird dinosaurs became extinct, an unprecedented opportunity for mammals became available and they began invading the ecological niches they left empty as they got older,” Bertrand said.
The researchers learned that the sense of smell – measured by the development of the olfactory bulbs of the brain – was vital to Paleozoic mammals as they grabbed new ecological roles. During the Eocene, other possibilities such as greater integration of sight, hearing, memory and motor control – associated with neoplasm development – became more critical to survival.
“There is a cost associated with having a large brain. The energy distributed to the brain represents 20% of the total energy distributed to the body. Thus, the evolution of large brains can only occur when the benefit of the large brain exceeds its maintenance costs, “said Bertrand.
Mammals now have the largest brain in the animal kingdom in relation to body size. Their brain development in Eocene occurred as competition for resources intensified and complex behavior became vital to the species’ survival, Bertrand said. Some Paleocene archaic extinctions have disappeared, being replaced by mammals that look more like those that live today.
With the extinction of predators and herbivorous dinosaurs, mammals began to take on these roles in the Old Age, an era of evolutionary experimentation. The panther-sized Arctocyon, one of the mammals studied, bore large canine teeth and ate meat and possibly plants. The blade-eating herbivorous Ectoconus, which was also studied, was heavily built with strong limbs and legs.
The study focused on placentas, by far the most common mammals. Fossils discovered in recent years in New Mexico, Colorado and France have provided information on Paleolithic mammals.
“Within 100,000 years after the extinction, the species’s wealth increased and mammals quickly became morphologically different,” Bertrand said. “Some Paleocene species were overall thick and quite different from modern groups, while others lived in trees and may have been possible ancestors of primates – the group that much later included humans. In the Paleocene, mammals do their own thing. “
Report by Will Dunham, Editing by Rosalba O’Brien
