Shark

A shark is a fish with a skeleton made of cartilage rather than bone. Sharks have existed for more than 400 million years, which makes them older than trees. The first sharks were swimming about tens of millions of years before the first tree appeared on land.^[1] For a long time, therefore, there was no wood anywhere, but there were sharks.

The Greenland shark

The Greenland shark, which lives in the cold depths of the North Atlantic and Arctic, may be the longest-living animal with a backbone. A 2016 study estimated the age of one at around 400 years, with a wide margin of uncertainty, and found that these sharks probably do not breed until they are well over a hundred.^[2] Some of the Greenland sharks swimming today were alive before the invention of the steam engine.

The Greenland shark swims very slowly, at about a kilometre an hour. Biologists believe the two facts may be connected.

Teeth

Sharks grow new teeth all their lives. When one falls out, the next one in a row behind it moves forward, like a conveyor belt. Some sharks get through tens of thousands of teeth in a lifetime. A shark never needs a toaster, a fork or a dentist, and is reported to be quite smug about all three.

See also

• Tree – younger than sharks
• Ocean – its home
• Jellyfish – older still
• Dolphin – a shark with better publicity

References

1. Fin, F. (1999). Before the Trees. Deep Press.
2. Slowe, S. (2016). “Four Hundred Years, Give or Take”. Journal of Old Fish 400: 1.
3. Conveyor, C. (2004). Teeth, Endlessly. Reef Books.