A shark cruising through open blue water seen from the side, with light rippling across its back

Beastfile · Marine Life

Sharks

Selachimorpha

Older than trees, older than Saturn’s rings, and barely a threat to anyone.

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Overview

Sharks predate trees. The lineage goes back more than 400 million years, which puts it before forests existed and, on current estimates of their age, before Saturn had rings. Around 500 species survive, most of them small, and the overwhelming majority have never harmed anybody: a handful of people die from shark bites worldwide in a typical year, against tens of millions of sharks killed by fishing. Their skeletons are cartilage rather than bone, their teeth are replaced continuously throughout life, and their snouts carry ampullae of Lorenzini, jelly-filled pores that detect the faint electrical fields of a hidden animal.

A shark swimming in clear water showing its dorsal fin and gill slits

Origin

Every ocean, from tropical reef shallows to polar water and the deep sea, with a few species entering rivers and freshwater lakes.

Habitat

Ocean

Notable Traits

•A lineage older than trees by tens of millions of years
•Cartilage skeleton rather than bone
•Teeth replaced continuously for life
•Electroreception through the ampullae of Lorenzini
•Skin covered in tooth-like denticles rather than true scales

Conservation

Poor and worsening. A large share of assessed shark and ray species are threatened, driven by targeted fishing, the fin trade and bycatch, and slow reproduction means depleted populations recover badly.