LIFE × EVOLUTION

The Teeth That Were Not Ours

~515 million years ago

Phanerozoic · Paleozoic · Cambrian

Conodonts were eel-shaped animals whose only common fossils are the millimetre-scale phosphate elements that lined their throats. Those elements worked: through their evolution, the apatite crystals inside them line up ever more precisely across the biting surfaces, exactly where a tooth needs to resist being crushed. They are the oldest mineralised tissue in the vertebrate lineage.

Why it matters

For decades this was read as proof that teeth came before jaws. X-ray tomography of the conodonts' own ancestors has undone it: their hard tissue is not the same tissue as our enamel, but an independent invention that resembles it. Which makes them more interesting, not less. Two lineages, hundreds of millions of years apart, arrived at the same solution to the same problem.

Dating & uncertaintyDisputed

Bone-like tissue in conodont elements pushed the first vertebrate hard tissue back from the Middle Ordovician to the Late Cambrian, around 515 Ma. Whether these elements are teeth in any real sense is contested: X-ray tomography of their ancestors suggests the resemblance to enamel is convergence, which would mean teeth came after jaws, not before them.

Sources

1. Murdock et al. (2013), Nature · The origin of conodonts and of vertebrate mineralized skeletons
2. Sansom et al. (1992), Science · Presence of the earliest vertebrate hard tissue in conodonts
3. Shirley et al. (2024), Nature Communications · Increasing control over biomineralization in conodont evolution

Earth history as one day

21:16:392 h 43 min before midnight

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