A species
Capybara
Hydrochoerus hydrochaeris
The world's largest rodent, a calm swimmer with riders on its back
You and the capybara last shared an ancestor about 90 million years ago (on 24 December, if life's history were one year).
Compare with something elseMeet the world's largest living rodent — a surprise cousin of the guinea pig and a distant relative of the house mouse. A grown capybara is about as big as a Labrador dog, about 1.2 metres long and about 35 to 66 kilograms. It has a barrel-shaped body, coarse brown fur and no tail you can see.
It is a calm swimmer. Its eyes, ears and nose sit high on its head, so it can keep its body hidden underwater with just those parts peeping out. Its feet are partly webbed, and it can stay underwater for up to five minutes to hide from hunters such as jaguars and caimans. It lives only near water, beside rivers, lakes and marshes in much of South America.
Capybaras are sociable grazers that often live together in herds of up to 40 animals. An adult munches through about 3 kilograms of grasses and water plants each day, wearing down teeth that keep growing. Birds happily ride on their backs, cleaning the fur in return for the free ride.
Speedy sprinter
It can run at up to about 35 kilometres per hour.
Shared baby care
Newborn pups can follow their mother and nibble plants almost at once, and every female in the group helps look after them.
Far from home
A small wild group has been seen in Florida, outside where it normally lives.