What is the largest rodent in the world?

The capybara, up to about 65 kilograms - a semi-aquatic South American rodent related to guinea pigs, with webbed feet, eyes and nostrils set high on the head for swimming, and a reputation for tolerating almost any other animal sitting on it.

That famous placidity is a by-product of being prey. Capybaras are eaten by jaguars, caimans and anacondas, and their strategy is vigilance in a group and a run for water rather than aggression, so they have no reason to react to anything that is not a predator. Photographs of birds, monkeys and other animals riding on them are largely a matter of an animal that gains nothing from objecting.

The Catholic Church was once asked to rule on them. Colonial-era Venezuelan clergy petitioned Rome about an animal that lived in water and, they argued, might count as fish for the purposes of Lent - and the classification appears to have been accepted, which is why capybara is still eaten during Lent in parts of Venezuela. The largest rodent that ever lived was considerably worse: Josephoartigasia, known from a Uruguayan skull, is estimated at around a tonne.