Prehistoric mammals prioritised bulking up over brain size to boost their chances of survival after the extinction of the dinosaurs, a new study has claimed.
It had been widely thought that mammals’ relative brain sizes generally increased over time in the wake of the devastating asteroid impact around 66 million years ago.
But University of Edinburgh researchers claim that for the first 10 million years after dinosaurs died out, mammals actually prioritised boosting their body size to adapt to radical shifts in the make-up of Earth’s animal kingdom.
Their findings show that the size of mammals’ brains, compared with their body weight, decreased following the Chicxulub impact that ended the reign of dinosaurs.
While much is known about the evolution of the brains of modern-day mammals, it has been – until now – unclear how they developed in the first few million years following the mass extinction.
Prehistoric mammals prioritised bulking up over brain size to boost their chances of survival after the extinction of the dinosaurs, a new study has claimed. A reconstruction of the Eocene mammal Hyrachyus modestus, a rhinoceros-tapir ancestor (left) and the Paleocene mammal Arctocyon primaevus, most closely related to living pigs and sheep (right), are pictured
University of Edinburgh researchers found that the size of mammals’ brains, compared with their body weight, decreased following the Chicxulub impact that ended the reign of dinosaurs
It had been widely thought that mammals’ relative brain sizes generally increased over time in the wake of the devastating asteroid impact around 66 million years ago
A team from the University of Edinburgh shed light on the mystery by performing CT scans on newly discovered fossils from the 10-million-year period after the extinction, called the Paleocene.
They found that the relative brain sizes of mammals at first decreased because their body size increased at a much faster rate.
Results of scans also suggest the animals relied heavily on their sense of smell, and that their vision and other senses were less well developed.
The team said this suggests it was initially more important to be big than highly intelligent in order to survive in the post-dinosaur era.
Around 10 million years later, early members of modern mammal groups such as primates began to develop larger brains and a more complex range of senses and motor skills.
This would have improved their survival chances at a time when competition for resources was far greater, the authors said, adding that the idea that big brains are always better to invade new environments or survive extinctions is misleading.
A team from the University of Edinburgh shed light on the mystery by performing CT scans on newly discovered fossils from the 10-million-year period after the extinction, called the Paleocene
They found that the relative brain sizes of mammals at first decreased because their body size increased at a much faster rate
Results of scans also suggest the animals relied heavily on their sense of smell, and that their vision and other senses were less well developed
Lead researcher Dr Ornella Bertrand, of the University of Edinburgh’s School of GeoSciences, said: ‘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.’
Because today’s mammals are so intelligent, it is easy to assume that big brains helped our ancestors outlast the dinosaurs and survive extinction — but that was not so, the team said.
Senior author Professor Steve Brusatte, also based at the University of Edinburgh, said: ‘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.’
The badlands of northwestern New Mexico are among the few places where scientists can find complete skulls and skeletons of the mammals that lived immediately after the mass extinction of dinosaurs.
Dr Thomas Williamson, Curator of Palaeontology at the New Mexico Museum of Natural History and Science, said: ‘Collecting and CT scanning many of the beautiful fossil skulls has led to this new understanding of what these bizarre animals were like and the evolution of the mammalian brain.’
The study has been published in the journal Science.
The team said this suggests it was initially more important to be big than highly intelligent in order to survive in the post-dinosaur era
Results of scans also suggest the animals relied heavily on their sense of smell, and that their vision and other senses were less well developed
KILLING OFF THE DINOSAURS: HOW A CITY-SIZED ASTEROID WIPED OUT 75 PER CENT OF ALL ANIMAL AND PLANT SPECIES
Around 66 million years ago non-avian dinosaurs were wiped out and more than half the world’s species were obliterated.
This mass extinction paved the way for the rise of mammals and the appearance of humans.
The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event.
The asteroid slammed into a shallow sea in what is now the Gulf of Mexico.
The collision released a huge dust and soot cloud that triggered global climate change, wiping out 75 per cent of all animal and plant species.
Researchers claim that the soot necessary for such a global catastrophe could only have come from a direct impact on rocks in shallow water around Mexico, which are especially rich in hydrocarbons.
Within 10 hours of the impact, a massive tsunami waved ripped through the Gulf coast, experts believe.
Around 66 million years ago non-avian dinosaurs were wiped out and more than half the world’s species were obliterated. The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event (stock image)
This caused earthquakes and landslides in areas as far as Argentina.
While investigating the event researchers found small particles of rock and other debris that was shot into the air when the asteroid crashed.
Called spherules, these small particles covered the planet with a thick layer of soot.
Experts explain that losing the light from the sun caused a complete collapse in the aquatic system.
This is because the phytoplankton base of almost all aquatic food chains would have been eliminated.
It’s believed that the more than 180 million years of evolution that brought the world to the Cretaceous point was destroyed in less than the lifetime of a Tyrannosaurus rex, which is about 20 to 30 years.
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