Life › Seas, forests & the move to land › Vertebrates move onto land (tetrapods)
Jawed fish
by c. 440 million years ago· Evolutionary innovation· Animals
Well establishedStrong fossil, genetic or geological evidence.
Fish that evolved hinged jaws and paired fins, the ancestors of nearly all living vertebrates, by about 440 million years ago.
See it on the Life map →What happened
Jaws probably formed from the front pair of the arches that supported the gills of jawless fish. A hinged jaw let fish bite, grip and crush, opening new foods and predatory lifestyles. Jawed fish also had paired front and rear fins for steering, forerunners of arms and legs. Possible jawed-fish scales date to the Late Ordovician; fossils from southern China, published in 2022, show varied jawed fish by about 436 million years ago.
Why it matters
Jawed vertebrates make up over 99% of living vertebrate species, from sharks to humans; jaws and paired fins underpin all later fish and four-legged animals.
The evidence (fossils, genes, rocks)
Silurian fossils from China such as Xiushanosteus and Entelognathus, embryo studies showing jaws develop from the first gill arch, and comparisons with living lampreys.
Still debated
Exactly when jaws arose, since early scales and teeth are hard to assign, and how the jaw hinge was reshaped step by step.
Inside this (3)
Connections (4)
▸Jawed fish include Placoderms: armored fishWell established
The connection
Placoderms were among the earliest jawed fish and dominated the Devonian. They had jaws and paired fins like all jawed fish, but covered the head and chest in bony plates. Fossils such as Entelognathus suggest the bones of our own jaw first appeared in placoderms.
When and how
Seas and rivers worldwide, about 430–359 million years ago; Entelognathus from Yunnan, China, described by Zhu Min and colleagues in 2013.
The evidence
Many well-preserved fossils, including three-dimensional specimens from Gogo, Australia, and family-tree analyses of jaw and skull bones.
Debates and open questions
Whether some placoderms had true teeth, as 2012 scans of fossil jaws suggested, or only toothlike bony points, is still debated.
▸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.
▸Jawed fish include Lobe-finned fishWell established
The connection
Lobe-finned fish belong to the bony fish, the branch of jawed fish that built skeletons of bone. Bony fish then split into ray-finned fish, which are most fish today, and lobe-finned fish, whose fleshy, bone-filled fins later became legs.
When and how
Split by about 425 million years ago, in Silurian seas; early forms such as Guiyu from Yunnan, China, described by Zhu Min and colleagues in 2009.
The evidence
Fossils showing a sequence of jaw, fin and skull changes, and DNA linking coelacanths and lungfish with tetrapods.
Debates and open questions
Some early bony fish mix ray-finned and lobe-finned features, making the exact split hard to place.
▸First vertebrates: jawless fish led to Jawed fishWell established
The connection
Over about 80 million years, jawless fish evolved bony armor, stronger skulls and, in some groups, paired fins. In one branch, the front pair of gill-supporting arches became a hinged jaw. That change, combined with paired fins, produced jawed fish by about 440 million years ago.
When and how
Ordovician and Silurian seas, roughly 485–440 million years ago; many key early jawed-fish fossils come from southern China.
The evidence
Fossils of armored jawless fish showing steps such as paired fins, and embryo studies in sharks and lampreys showing how jaws develop.
Debates and open questions
Whether jaws truly came from gill arches is debated, as is which jawless group is closest to jawed fish.