Sharks have been around far longer than trees, having survived several mass extinction events.

The longer version

Cartilaginous fish appeared in the oceans hundreds of millions of years ago, well before the first woody plants had evolved the tissue that lets a trunk stand upright. Because shark skeletons are made of cartilage rather than bone, they fossilise poorly, so most of what survives is teeth and scales.

That patchy record still shows a body plan that worked early and kept working. Sharks have no swim bladder, relying instead on a large oily liver and constant motion, and their skin is covered in tooth-like denticles that reduce drag and resist damage. The group has passed through several mass extinctions, including the one that ended the age of dinosaurs, with surprisingly little change to the basic design.

Where this entry sits

This collection gathers small surprises about mammals, reptiles, amphibians, birds, fish, insects, and the pets living alongside people. Expect odd details about senses, anatomy, and everyday behaviour that many people never notice in the animals around them. The full list sits on the Animals page, where every entry is listed in order.