by Greg Mayer

You may remember the Looney Tunes cartoon character Sylvester the Cat. One of his recurring story lines was that he mistook a kangaroo for an enormous mouse, which became his nemesis, as his efforts to catch it always ended in humiliating failure. In real life, while there are some big mice, the world’s record rodent is the capybara, a prodigious South American species that resembles a giant guinea pig. The capybara below clearly knows that cats need fusses, and enjoys giving them, but the cat’s face seems torn between discretion and valor in reaction to the amicable rodent.

Capybaras (Hydrochoerus hydrochairis) are found from Panama to Argentina. (There seems to be some debate over whether the Trans-Andean ones in Panama and northwestern South America should be recognized as a distinct species, isthmius.) They are aquatic, and their major predators include caimans and jaguars (so they’re probably not quite as friendly to all cats).

The biogeographic history of capybaras and their close South American relatives—which include porcupines, guinea pigs and chinchillas—is quite interesting. The group, called caviomorphs, have their nearest relatives in the Old World, a group of rodents that includes the naked mole rats and the Old World porcupines. (New World and Old World porcupines are not that closely related; spiny hair has evolved multiple times in rodents.)

The American and Old World groups together are called hystricognaths. Molecular and fossil data indicate that the New World caviomorphs arrived in South America in the mid-Tertiary (about 40 mya), when South America was an island continent separated from Africa by the Atlantic. Thus the caviomorphs colonized the New World over the ocean via what Darwin called “occasional means of transport” (in this case, probably natural rafts produced by flooding from major rivers). They are thus one of the few mammalian groups that reached South America between the time it broke loose from Gondwanaland until it connected with North America through Panama in the Great American Interchange.

The picture above, which was sent to me, appears to come from a website about capybaras as pets. There’s even a book about cats and capybaras living together, Celeste and the Giant Hamster.  (I think they really look more like giant guinea pigs, which are also caviomorphs.)

h/t  A. Junker

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Marshall, L.G. 1988. Land mammals and the Great American Interchange. American Scientist 76:380-388. (pdf)

Mones, A. and J. Ojasti. 1986. Hydrochoerus hydrochairis. Mammalian Species 264:1-7. (pdf)

Poux, C., P. Chevret, D. Huchon, W.W. de Jong and E.J.P. Douzery. 2006. Arrival and diversification of caviomorph rodents and platyrrhine primates in South America. Systematic Biology 55:228-244. (pdf)