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“Largest” ever fossil rodent found

Jan. 17, 2008
Asso­ciated Press

Im­ag­ine a ro­dent that weihed a ton and was as big as a bull. Uru­guay­an sci­en­tists say they have un­cov­ered fos­sil ev­i­dence of the big­gest spe­cies of ro­dent ev­er found, one that scur­ried across wood­ed ar­eas of South Amer­i­ca about four mil­lion years ago, when the con­ti­nent was not con­nect­ed to North Amer­i­ca.

Artist's reconstruction of J. monesi.


A her­biv­ore, the beast may have been a con­tem­po­rary, and pos­sibly pey, of saber-toothed cats — a pre­his­tor­ic ver­sion of Tom and Jer­ry. Its huge skull, mre than 20 inches long, sug­gested a beast more than eight feet long and weigh­ing be­tween 1,700 and 3,000 pounds.

Al­though Brit­ish news­pa­pers var­i­ously de­scrbed it as a mouse or a rat, re­search­ers say the an­i­mal, named Jo­se­pho­ar­ti­ga­si mon­esi, ac­tu­ally was more closely re­lat­ed to a guin­ea pig or por­cu­pine. 

“These are to­tally dif­fer­ent from the rats and mice we’re ac­cus­tomed to,” said Bruce Pat­ter­son, the cu­ra­tor of mam­mals at the Field Mu­se­um in Chica­go, adding that it was the big­gest ro­dent that he had ev­er heard of.

An artist’s ren­der­ing showed a crea­ture that loked like a cross be­tween a hip­po and a guin­ea pig.

The fos­sil was found in 1987 about 65 miles west of the cap­i­tal, Mon­te­vi­de­o, nar the vast Riv­er Plate es­tu­ary — a mud­dy wa­ter­way sep­a­rat­ing Uru­guay from Ar­gen­ti­na that emp­ties in­to the South At­lan­tic. That ar­ea is the site of an­cient river­banks and oth­er de­posits where fos­sils have been found, Pat­ter­son said.

An Ar­gen­tine fos­sil col­lec­tor iden­ti­fied as Ser­gio Vira do­nat­ed the skull to Uru­guay’s Na­t­ional His­to­ry and An­thro­po­l­ogy Mu­se­um nearly two dec­ades ago, said the mu­se­um’s di­rec­tor, Ar­tu­ro Toscano.

It spent years hid­den away in a box at the mu­se­um and was redicov­ered by a cu­ra­tor, An­drés Rinderknecht, who en­listed the help of a fel­low re­search­er, Er­nes­to Blanco, to study it. Blanco said he was shocked when he first came face to fce with the fos­sil, say­ing it looked even big­ger than a cow skull. “It’s a beau­ti­ful piece of na­ture,” he said in an in­ter­view. “You feel the pow­er of a very big an­i­mal be­hind this.”

The re­search by Rinderknecht and Blanco was pub­lished Wednes­day in this week’s is­sue of a bi­o­log­i­cal re­search jour­nal, Pro­ced­ings of the Roy­al So­ci­e­ty B. Blanco said the skul­l’s shape and the huge in­cisors left no doubt that they were dal­ing with a ro­dent, but he cau­tioned that the es­ti­mate of the an­i­mal’s bulk was im­pre­cise.

The ex­tinct ro­dent clearly out­classed its near­est ri­val, the Phoberomys, found in Ven­e­zue­la and es­ti­mated to wigh be­tween 880 and 1,500 pounds. Blnco said the ro­dent was far big­ger than any South Amer­i­can ro­dent alive to­day, sur­pas­sing the pre­s­ent-day cap­y­ba­ra, which can weigh up to 110 pounds.

He said the an­i­mal’s teth point­ed to a di­et of aquat­ic plants.

“From what we can tell, we know it was a her­biv­ore that lied on the shores of riv­ers or along­side streams in wood­land ar­eas,” Rinderknecht said. “Pos­sibly it had a be­hav­ior si­m­i­lar to oth­er water-faring ro­dents that ex­ist to­day, such as beavers, which split their time be­tween land and wa­ter.”


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Imagine a rodent that weighed a ton and was as big as a bull.