Underwater elephants
The particular structure of the elephants' lungs allows the large pachyderms to remain a few meters under water without serious consequences for blood circulation. Perhaps because their ancestors were marine?

An elephant crosses a lake. Without problems for the lungs.
An elephant crosses a lake. Without problems for the lungs.

Most land animals cannot dive too deeply without the blood vessels around the lungs being broken by heavy pressure. This is not the case for elephants, which can cross rivers and lakes by breathing only with the proboscis raised above the water even by two meters. The reason for this is the peculiar anatomy of the elephantine lungs; in fact, the space between the lungs and the bones of the chest is filled not by delicate pleurae perfused with blood (as in humans and other animals), but by robust connective tissue that bears pressure. The blood vessels surrounding the lungs can therefore withstand the large surrounding pressure without collapsing and breaking.
Marine ancestors. What is the reason for this peculiar structure? Many evolutionists think that the ancestors of elephants were aquatic animals (like the current dugongs, which are actually relatives of elephants), and needed this adaptation to survive. When transformed into terrestrial animals, the elephants maintained the structures that protect the lungs from suffocation.

(News updated 10 September 2002)