Sharks Are Older Than Trees

Step 1 of 5

Sharks show up very early, and mostly as teeth.

A shark skeleton is cartilage, which rots. Teeth are mineral, which does not — and a shark sheds thousands in a lifetime. So the fossil record of sharks is enormous and it starts around 450 million years ago, in oceans that had nothing recognisable in them.

Because they shed teeth constantly, a single shark can leave more fossils than an entire population of bony fish.

Step 2 of 5

Trees needed an invention that took much longer.

Growing tall means solving two problems at once: lifting water many metres against gravity, and not falling over. The answer to both was lignin, a stiffening compound that turns a plant stem into wood. Until something evolved lignin, nothing on land could be a tree.

Step 3 of 5

So sharks had a sixty-million-year head start.

That gap is longer than the whole time since the dinosaurs died out. For sixty million years there were sharks in the sea and nothing taller than a shrub anywhere on land.

Step 4 of 5

Sharks are older than several things in the sky, too.

Saturn's rings look ancient and are probably only a hundred million years old or so. Polaris, the current North Star, is a young star. The Atlantic Ocean did not exist. Sharks predate all of them.

The age of Saturn's rings is actively debated, and Cassini's measurements pushed the estimates young. It is a live question, not a settled one.

Step 5 of 5

Being old is not the same as being unchanged.

People call sharks living fossils, and it is misleading. Modern sharks are not the 450-million-year-old ones; the lineage has produced and lost hundreds of forms. What is old is the group and the basic design — cartilage, replaceable teeth, electrical sensing — not the individual species.