The first jaws: placoderms take a bite out of the world
What happened
The oldest known placoderms, an armored, extinct group of fish, appear in the fossil record from the late Early Silurian in China, and they carried something no vertebrate before them had: a jaw. The University of California Museum of Paleontology places placoderms as the earliest branch of the gnathostomes, the jawed vertebrates that include every fish, amphibian, reptile, bird, and mammal alive since. Odd as it sounds, placoderms never evolved teeth. Bony plates built into the jaw itself did a tooth's job instead, some wearing into naturally self-sharpening edges as the animal fed.
Why it matters
A jaw turns a mouth from a simple filter or sucking tube into an active weapon, letting an animal grip, crush, and actively hunt rather than passively scavenge. Every jawed vertebrate on Earth today, humans included, is still running a version of the hinge placoderms debuted here.
How we know
Placoderm fossils preserve heavy bony head and jaw armor exceptionally well, since bone fossilizes far more readily than the mostly cartilaginous skeletons of earlier jawless fish. Comparing that jaw architecture across dozens of placoderm species, and against the jawless fish that came before them, is what places placoderms at the root of the jawed-vertebrate family tree.
Sources
- University of California Museum of Paleontology. Introduction to the Placodermi · Reputable sourceucmp.berkeley.edu · The domain "ucmp.berkeley.edu" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Part of a timelineLife Conquers the Land7 events · The 160 million years between the Cambrian explosion and the dinosaurs, when plants, jaws, limbs, and the amniotic egg turned a planet of water into one of forests and dry land.View all →