Sharks, rays, and chimaeras are collectively known as cartilaginous fish, because instead of bones, they have cartilage material like humans have in our noses and ears. That certainly seems to work out well for them, given their long reign and the diverse niches they occupy, but it’s not so great for humans wanting to draw a picture of ancient sharks.

In particular, it raises the question of how palaeontologists even know sharks evolved 450 million years ago , or are aware of the size of megalodon, the giant shark that lived 23 to 3.6 million years ago. When you read that megalodons were two to four times as long as existing great white sharks, is that just a guess?

In fact, there are a few ways sharks leave a presence in the fossil record. The most common and important is their teeth.

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