Life › Seas, forests & the move to land › Jawed fish
Sharks
c. 420 million years ago to today· Organism or group· Animals
Strong evidenceGood evidence; dates or details still being refined.
Cartilage-skeleton jawed fish that appeared by about 420 million years ago and have survived four mass extinctions since.
See it on the Life map →What happened
Sharks and their relatives, rays and chimaeras, have skeletons of cartilage, often stiffened with minerals, and teeth that are shed and replaced throughout life. Shark-like scales appear in Silurian rocks, possibly earlier; the extinct 'spiny sharks' (acanthodians) are now seen as early members of the shark line. Sharks are older than trees, though most living shark groups arose much later, in the age of dinosaurs.
Why it matters
Their survival through four mass extinctions makes them a benchmark for resilience, and as top predators they still shape ocean food webs.
The evidence (fossils, genes, rocks)
Mostly teeth, scales and fin spines, since cartilage rarely fossilizes; rare whole skeletons such as Doliodus from Canada, about 400 million years old; and DNA from living species.
Still debated
When the shark lineage began, since the earliest scales are hard to assign, and how much the first sharks resembled living ones.
Connections (2)
▸Jawed fish include SharksWell established
The connection
Sharks are one of the two surviving great branches of jawed fish; the other is the bony fish, which includes us. Sharks have skeletons of cartilage, while bony fish built theirs of bone. Fossils suggest the shark line may have lost bone its ancestors had.
When and how
The shark and bony-fish lines had split by roughly 440 million years ago, in early Silurian seas; fossils from southern China published in 2022 include early shark relatives.
The evidence
Fossil scales, teeth and spines, plus DNA from living sharks, rays and chimaeras that places them on a separate branch from bony fish.
Debates and open questions
Whether cartilage is the original state; a 2020 Mongolian fossil, Minjinia, with internal bone suggested bone came first and sharks lost it.
▸Sharks survived The Great Dying (end-Permian extinction)Well established
The connection
Sharks and their relatives lost many lineages in the Great Dying, but several groups, including the hybodonts and the ancestors of today's sharks and rays, made it through. In the emptied Triassic seas they diversified again, eventually producing the modern shark groups.
When and how
Oceans worldwide about 252 million years ago; shark teeth and fin spines appear in earliest Triassic marine rocks on several continents.
The evidence
Fossil teeth and spines below and above the boundary, plus family trees that trace living sharks back to Paleozoic ancestors.
Debates and open questions
How many shark lineages survived, and why, are uncertain. Cartilage skeletons rarely fossilize, so counts rely heavily on teeth.