LIFE × EVOLUTION

Jaws Without Teeth

~382 to 358 million years ago

Phanerozoic · Paleozoic · Devonian

Placoderms wore bone plates over the head and shoulders, hinged to the body at the neck. The largest, Dunkleosteus, had no teeth at all. It sheared with bony blades that sharpened themselves as they wore against each other, driven by a skull whose bones swing as a linkage: four rigid pieces on four joints, so that one movement opens the mouth wide and fast.

Why it matters

These were the first vertebrates built to catch and cut up prey that could dodge. How hard they bit is being recalculated: the famous figure came from a model that hung the jaw muscles on the roof of the skull, and a fresh look at the anatomy puts them elsewhere, on cartilage that rarely fossilises. The mechanism stands. The number does not.

Dating & uncertainty

Placoderms span the whole Devonian; the giant predators belong to its second half and are gone by its end. Their famous bite force, estimated at over 5,000 newtons, comes from a model whose muscle attachments have since been reconstructed differently, and the figure is now under revision.

Sources

1. Anderson & Westneat (2007), Biology Letters · Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator
2. Engelman et al. (2025), The Anatomical Record · Functional anatomy, jaw mechanisms, and feeding behavior of Dunkleosteus terrelli (Placodermi, Arthrodira)
3. Lebedev et al. (2022), Journal of Paleontology · Feeding in the Devonian antiarch placoderm fishes: a study based upon morphofunctional analysis of jaws

Earth history as one day

21:58:502 h 1 min before midnight

if Earth’s 4.54 billion years were compressed into a single day