Bison-sized rodent may have used teeth like elephant tusks

Capybaras, here in Colombia, are the world’s largest rodents today. But even they would have been dwarfed by Josephoartigasia monesi. Photo by: Rhett A. Butler.

The world’s largest rodent today is the capybara (Hydrochoerus hydrochaeris), weighing in at around at about 45 kilograms (100 pounds), though the record breaking female weighs in at 91 kilograms (201 pounds). But that’s nothing compared to the biggest rodent ever to live. Discovered in Uruguay in 2008, Josephoartigasia monesi may have weighed in at 1,000 kilograms (2,200 pounds) would have been more than 20 times bigger than a capybara and 3,000 times bigger than a really big black rat. Comparatively speaking, Josephoartigasia monesi would have been about the size of a bison.

But how did this mega-rodent behave? New research in the Journal of Anatomy suggests Josephoartigasia monesi may have used its teeth like an elephant uses its tusks. The researchers from University of York and The Hull York Medical School (HYMS) employed computer modelling and a CT scan of the skull to estimate the bite force of the giant rodent’s teeth.

“Josephoartigasia monesi had a bite of 1389 N at the incisors, rising to 4165 N at the third molar,” the researchers write. The N refers to a “newton,” or standardized measurement of force. Josephoartigasia monesi‘s bite force is around that of a tiger’s; in contrast, human bite force is about 720 N.

Most notably, though, the researchers found that the teeth were structured so they could handle much more stress than they applied.

“The incisors of Josephoartigasia monesi were overengineered with respect to feeding; that is, they could resist much greater forces than could ever be generated by the masticatory muscles. Thus, it has been suggested that Josephoartigasia monesi may have regularly used its incisors for activities other than feeding, such as digging for food or defense against predators,” the researchers write.

This leads the researchers to compare the possibly feeding ecology of Josephoartigasia monesi to an elephant’s.

“That is, it could process a broad selection of tough vegetation with the short molar tooth row, while using its unusually strong incisors like tusks for defence and digging for roots,” the researchers write.

Josephoartigasia monesi, which only based on a single skull to date, lived around 2-4 million years ago. Its closest living relative is the pacarana (Dinomys branickii), also known as Count Branikii’s terrible mouse, weighing in at a still impressive 15 kilograms (33 pounds). The species listed as Vulnerable by the IUCN Red List due to habitat destruction and hunting.

Pacaranas are large, slow-moving, nocturnal rodents that inhabit the forests of northern and central Bolivia. The species is listed as Vulnerable by the IUCN, and is the sole member of the Dinomyidae family. Photo by Benjamin Frable.

Citations:

Cox, Philip G., Andrés Rinderknecht, and R. Ernesto Blanco. “Predicting bite force and cranial biomechanics in the largest fossil rodent using finite element analysis.” Journal of anatomy (2015).

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