福利姬自慰

The discovery by Associate Professor Mary Silcox and Ornella Bertrand shows that brain size does not necessarily increase over time (composite image courtesy Perry Sheppard)

Ancient rodents with brains of unusual size

鈥淭he brain was certainly larger than we expected,鈥 researcher says after examining ancient skulls

If new 福利姬自慰research on the brains of an ancient rodent tells us anything, it鈥檚 that bigger does not necessarily mean better. 

福利姬自慰Scarborough PhD candidate Ornella Bertrand along with Associate Professor Mary Silcox and undergraduate student Farrah Amador-Mughal recently reconstructed two endocasts of Paramys, the oldest and best-preserved rodent skulls on record. What they found was surprising.

鈥淭he brain was certainly larger than we expected considering the time period,鈥 says Bertrand. 鈥淓ven more surprising is that it was almost as large, and in some cases larger, than primitive primates of the same time period.鈥  

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 鈥渉igher鈥 brain functions like sight and hearing. 

鈥淭his tells us that something is going on in the neocortex of early primates that is not observable in early rodents.鈥 says Bertrand. 鈥淭he changes in the neocortex of rodents occurred later in time and with less intensity than in primates.鈥 

Silcox adds, 鈥淚t also sheds some light on what鈥檚 unique about primate brains 鈥 they were not always exceptionally large, but they were certainly 鈥榮mart鈥.鈥 

One of the specimens of Paramys was a large rodent by modern standards 鈥 about three kilograms, roughly the size of a small cat 鈥 that lived during the mid-Eocene, some 47 to 49 million years ago. Bertrand and Silcox also examined the skull of another with a body mass of about one kilogram that lived around 50 to 52 million years ago. 

The goal of the research was to better understand brain evolution in early rodents. While there鈥檚 been some research looking at how the neocortical surface of primates has increased over time, practically nothing prior to this has been done on rodents. 

What fascinates both Bertrand and Silcox is that Paramys鈥檚 brain was larger than some later occurring rodents, which contradicts the idea that brains generally increase in size over time.   

鈥淚t鈥檚 been assumed for a while that mammal brain size increases over time. The idea is that it鈥檚 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,鈥 says 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. 

鈥淪ize is certainly important, but we鈥檙e starting to look at different measures that give us a more nuanced understanding of how brains, especially in primates, evolved over time,鈥 says Silcox.   

The research, which is , will be published in the upcoming edition of the journal Royal Society B

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