Ancient rodent's brain was big but not 'smart': Study

Toronto: Early rodents that lived about 50-million years ago had large brains that were even bigger than some primitive primates of the same period, according to a new study.

Researchers at the University of Toronto reconstructed two endocasts of Paramys, the oldest and best-preserved rodent skulls on record. "The brain was certainly larger than we expected considering the time period," said PhD candidate Ornella Bertrand.

"Even more surprising is that it was almost as large, and in some cases larger, than primitive primates of the same time period," said Bertrand.

The key difference is that Paramys was relatively smaller than even the most primitive primates in the neocortex region, the part of the brain that deals with 'higher' brain functions like sight and hearing. "This tells us that something is going on in the neocortex of early primates that is not observable in early rodents," said Bertrand.

"It also sheds some light on what's unique about primate brains - they were not always exceptionally large, but they were certainly 'smart'," said Associate Professor Mary Silcox.

One of the specimens of Paramys was a large rodent by modern standards - about three kilogrammes, roughly the size of a small cat - that lived during the mid-Eocene, some 47 to 49 million years ago.

Researchers also examined the skull of another with a body mass of about one kilogramme that lived around 50 to 52 million years ago. Paramys's brain was larger than some later occurring rodents, which contradicts the idea that brains generally increase in size over time. It's been assumed for a while that mammal brain size increases over time. The idea is that it's probably an evolutionary arms race because if prey become smarter predators have to adapt. But these animals were already pretty smart prey items to begin with," said Silcox.

The research also shows that the obsession with brain size, especially in the human paleontological literature, makes little sense since size is not the only indicator of intelligence, researchers said. The research was published in the journal Royal Society.

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