My what strange teeth you have Grandma

Bones are very useful. Without them you'd be in a sorry state. Leap out of bed first thing in the morning and, thanks to gravity, you'd end up on the floor as a rather sad pile of floppy skin and quivering muscle. Luckily, you do have bones. You, along with all other humans, belong in the group of animals known as 'vertebrates' or 'backboned animals'. This includes mammals, reptiles (snakes and lizards), amphibians (like frogs) and fish.

Evolving a backbone

The first vertebrates were very strange. This was because they didn't have a backbone at all. What makes them a vertebrate is a thread, called a notochord, that ran down where their backbone would have been. Fortunately for them, they lived in the sea, so they didn't need a backbone so much. The sea held them up. So, why do scientists think that they had backbones? Good question.

Pile Worms Teeth

The oldest vertebrate fossils were fish. Now, when you think of a fish you probably imagine something covered in batter, snuggling up to a pile of chips, and sprinkled with salt and vinegar. Surprising as it may seem, this isn't a bad picture of what the first fish looked like more than 500 million years ago. OK, you can take away the chips (or better still, eat them), and imagine that the batter was its skin. (We'll come back to the vinegar later.) What's inside the batter is fish flesh. The next time you tuck into your plate of fish and chips, look carefully at the fish. It's not a solid single lump of flesh. You'll see that you can pull it apart into segments. If your piece of fish is large enough, you'll see that each GooA WaW I This to Aoffer of these segments ^ a-S^-d Of* !

is V-shaped.

is V-shaped.

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This is one of the things, along with the notochord, that makes the fish a vertebrate. And your piece of fish from the fish shop is unlikely to have a backbone, just like the first fish fossils.

These oldest of all fish fossils have only just been discovered, near a place called Chengjiang in southern China. These first fish swam in the sea with Hallucigenia and Anomalocaris. They are called Myllokunmingia and Haikouichthys. As well as not having a backbone, these fish didn't have any teeth or jaws. They couldn't

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even have given you a gummy suck, let alone a bite. They did have fins, though.

Sixty million years later (that's about 480 million years ago), fish had begun to look a bit more fish-like. At this time, a shallow sea covered much of central Australia. While trilobites crawled over the mud and sand at the bottom of this sea, fish called Arandaspis and Sacabambaspis (which has to be one of the best names thought up for a fossil) swam above them. They had a few fins, so they could swim reasonably well. These, and other fish of the time, were certainly strange. Even though they still didn't have jaws, they did have teeth. Mmmmm. So where do you think they kept them? Weird as it may seem, they wore them on their bodies, which were covered by hundreds of tiny tooth-like scales. As you can imagine, these scales or teeth were no use for biting or chewing. It is more likely they formed an armour that helped protect the fish from being eaten. Trying to chew and swallow something covered by hundreds of teeth could be a bit painful.

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