Toronto: A study involving an ancient rodent's brains has found that bigger does not necessarily mean better, at least when it comes to animals.

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 Ornella Bertrand, who along with associate professor Mary Silcox and undergraduate student Farrah Amador-Mughal conducted the study. 

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

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," Bertrand said. 

"The changes in the neocortex of rodents occurred later in time and with less intensity than in primates."

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

What fascinated both Bertrand and Silcox was that 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," says Silcox.

The research also showed that the obsession with brain size, especially in the human paleontological literature, makes little sense since size is not the only indicator of intelligence.

The research was recently published online in the journal Royal Society B.