Researchers find evidence of a rodent the size of a Saint Bernard with a tiny brain in Brazil

According to José Ferreira and Leonardo Kerber, researchers at the Federal University of Santa Maria in Brazil, there was once a giant rodent in South America that was the size of a Saint Bernard dog, but with a brain no bigger than a golf ball. Paleontology World says that the rodent the team discovered is the largest ever to have lived in South America.

That rodent is Neoepiblema acreensis, which is related to chinchillas. It lived about 10 million years ago and when Ferreira and Kerber and their team got curious about the brain of Neoepiblema acreensis, they looked inside two fossil skulls using computerized tomography.  

Researchers with Universidade Federal de Santa Maria, Universidade Federal do Acre, and the Paleontological Institute and Museum compared the brain sizes of a variety of creatures that weighed different amounts and calculated the ‘encephalization quotient,’ or the difference between what they expected the brain size to be, and what it actually was for an animal of a specific weight. In the quotient, an animals’ brain was smaller than expected if the value was less than one.

Using that encephalization quotient, the team estimates that N. acreensis brains weighed 47 grams. The researchers revealed that for this giant rodent, the encephalization quotient of one individual studied was 0.20. Another’s encephalization quotient was 0.33. This revealed that the brain of N. acreensis’ was “unusually puny” in comparison to its body size. Paleontology Today notes that the rodent was 1.5 meters in length.

In contrast, rodents that you find now in South America have an average encephalization quotient of more than 1.05.

The bigger the brain the greater the energy expenditure, so a small brain was probably advantageous for these rodents. 

“The adaptive value of a low energetic cost and other ecological factors could explain the presence of a small brain in this giant rodent –a pattern we also hypothesize for other Neogene giant rodents,” the abstract of the research article states.

Giant crocodiles in the area swamps may have been an issue, but these rodents weren’t targeted by man predators. And that, researchers suggest, may be part of the reason their brains were so small – it wasn’t worth the maintenance cost.