EVOLUTION × LIFE

The First Jaws

~439 to 419 million years ago

Phanerozoic · Paleozoic · Silurian

Two finds in South China, three million years apart, catch jawed vertebrates at the start. The older is a set of tooth whorls: teeth in paired rows that were never shed, new ones added on the inside as the animal grew. The younger is a whole fauna of complete fishes small enough to hold in a hand, armoured placoderms and early sharks among them. Jaws turned filter feeders into hunters.

Why it matters

The bones in your own jaw were named before anyone knew how old they were. A placoderm of 419 million years, dug out of Silurian rock in China, carries a premaxilla, a maxilla and a dentary in the same places you do. Those bones are therefore older than the split between bony fishes and sharks, and sharks lost them rather than never having had them.

Dating & uncertainty

Isolated tooth whorls at about 439 Ma are the earliest direct evidence, the oldest complete jawed fishes are 436 Ma, and molecular estimates place the origin earlier still, in the Ordovician.

Sources

1. Andreev et al. (2022), Nature · The oldest gnathostome teeth
2. Zhu et al. (2022), Nature · The oldest complete jawed vertebrates from the early Silurian of China
3. Zhu et al. (2013), Nature · A Silurian placoderm with osteichthyan-like marginal jaw bones

Earth history as one day

21:40:452 h 19 min before midnight

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