A new theory of mammalian evolution after the extinction of the dinosaurs.

In the 1970s, paleontologists envisioned a synchronous evolution of mammalian external morphology and brains that increased immediately after the extinction of the dinosaurs. However, the new work on the fossilized skulls suggests independent developments.

twist of fate

66 million years ago, the dinosaurs disappeared after a collision with a giant meteorite (the most plausible hypothesis to date) in the Yucatan Peninsula in Mexico. Deprived of their former main predators that dominated the surface of the planet, the surviving fauna opened up a new world that favored its development. Prior to this mass extinction, mammals lived in nests to escape the dinosaurs, unable to grow larger for several tens of millions of years. Then an event of catastrophic proportions worked for them, allowing the surviving species to breed on the surface and develop new territories. Except, freed from predation by the elite, some mammals sometimes reached colossal sizes. Today, mammals are the vertebrates with the highest ratio of brain size to body size.

Significant Changes for Mammals

Following the recent discovery of fossilized mammalian skulls, geologist Ornella S. Bertrand of the University of Edinburgh (UK), lead author of the study published in April 2022, agrees that the mammalian body evolved first, between 66 and 56 million years BC. On the other side, the enlargement of the brain would have declared itself later, between -56 and -32 million years ago. This heightened thinking was directly related to the need to adapt to increasingly complex environments, such as increasing competition for food and saturation of ecosystems, which necessitated the search for new solutions to certain survival problems that were still new.

Credits: LuFeeTheBear/istockphoto

“[Les chercheurs]studied the rate of encephalization in Paleocene mammals and found […] that body size was the first to increase, allowing niches to be filled after the extinction of the dinosaurs […]. Only later, during the Eocene, did brain size begin to increase, probably due to the need for more cognition in increasingly complex environments. This has led to the modern brain with a high degree of encephalization, including in humans.”explains Ornella S. Bertrand.

This conclusion follows from analysis of 34 mammalian skulls dating from the Paleocene (from 66 to 56 million years BC) from New Mexico and Colorado (USA). Their tomographic images (3D computerized reconstruction of the skulls) allowed the researchers to hypothesize a late brain evolution in relation to muscles, in part due to image detail revealing the neocortex and olfactory bulbs. . Thus, these individual events would have been separated by about ten million years. However, this theory is still being discussed in the scientific community.

dakotaraptor dinosaur
Dakotaraptor, a Cretaceous theropod found in South Dakota, USA. Credits: Warpaintcobra/iStock

Paleontological research still has much to learn about the species that inhabited the Earth. Among other things, we just discovered that some types of land dinosaurs had feathers. Therefore, the idea of ​​them that we have can still develop.

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