Armed to the teeth
The account below is based on an article written for children
by Mark Purnell, originally published in Rockwatch (1997).
Among our early Palaeozoic ancestors was a creature known as a
conodont; it was small in size, but it had a surprisingly big
Almost all the fossils that are familiar to us, such as ammonites, bivalves, trilobites and corals have their own particular types of hard parts, but their shells are not like the hard parts that make up our skeletons. Our hard parts are made of enamel, dentine and bone, and the only animals to make their skeletons from these materials are known as the vertebrates. The mystery of how and when we got our bones and teeth is one that goes all the way back to the origin of vertebrate animals; the day, sometime during the Cambrian Period, when the ancestor of you, me and all other members of our corner of the animal kingdom first wriggled its way across the sea floor.
What was this important animal like? Well, unfortunately it had no bones or teeth, and so no fossils have been found. But from what we know about the most primitive fishes alive today, we can guess that it was probably small, a few centimetres long, and rather eel-like in appearance. Along its body ran a stiffening backbone-like structure, and it had a brain and eyes, and a tail with fins. Without any fossils to help us to understand them, there are many questions about these early animals that are difficult to answer. How did they feed? where did they live? when and why did they first grow teeth and other hard parts? Palaeontologists have been investigating these questions for more than a hundred years, but with little real success.
This picture, taken using a scanning electron microscope, shows
four conodont elements stuck on a pinhead.
Recently, important clues about our very early vertebrate ancestors have been turning up in unexpected places. They have come from scientific study of a weird group of long-extinct, microscopic fossils called conodonts. What, I hear you ask, is a conodont? It's a good question, and until a few years ago no-one really knew the answer. There were plenty of guesses around, though. Some conodont microfossils, as you can see in the picture to the left, look a bit like short spiky combs, and some palaeontologists thought that they might have been used by a kind of extinct worm to collect microscopic plankton for food. Or perhaps they were used by ancient sea snails to scrape up slime from rocks, much as limpets do now. Other conodont microfossils look more like claws, and this led some people to suggest that they may have been used for grabbing and stabbing at food. Some scientists even had the idea that they might be bits of plants! Lots of conodont microfossils look like teeth, and one of the best ideas was that they were the teeth of some type of extinct simple fish-like creature. But even this idea was really only a sensible guess. There was just not enough evidence to decide what they were.
Conodont microfossils were discovered almost 150 years ago, and since then, the hunt has been on for specimens that might tell us more about them. Palaeontologists didn't have much luck until 1983 when, quite by accident, new fossil conodonts surrounded by interesting squiggly outlines were found on the surfaces of 330 Million year old rocks in Scotland.
A sausage in the sea
These fossils are some of the rarest known; even after another 13 years of looking there are still only 12 in the whole world. They are not as spectacular as a Tyrannosaurus, or as beautiful as a perfect ammonite, but these fossils are more amazing because what these squiggles show is the body of the conodont. You might not consider that that is particularly amazing, but think about this: a conodont's body had no bones, and what the fossils have preserved is the muscles and gristly bits of the body, and even traces of the eyes! Some of these fossils are more than 400 million years old, so they make Egyptian mummies look like they died yesterday, but it is the chances of fossilizing the soft-parts of the body that make these fossils really amazing. It's a bit like throwing a sausage into the sea; how long do you think it would last? Fish and crabs would nibble at the sausage and after a few hours, the whole thing would be gone. Even if the fish didn't make a meal of it, after only a few days bacteria would have rotted it down to nothing. So you can see that the geological equivalent of preserving a sausage for 400 million years is even less likely than you winning the lottery! Yet that is what has happened to the fossils of the conodont body.
So, conodonts are...
The clues from these fossils tell us that the body of a conodont was a few centimetres long, and rather eel-like in appearance, with a stiffening backbone-like structure, a tail with fins, and eyes (pictured on the right). In fact, it was very like the idea of what the first vertebrates looked like, and we now think that conodonts were themselves primitive vertebrates. The big difference, though, is that their mouths were full of tiny conodont teeth that we now find as microfossils. In the light of the new ideas about conodonts, these tooth-like remains have been studied very intensively. High powered Scanning Electron Microscopes that can magnify them thousand of times have been used to reveal that the microfossils are made up of enamel and dentine, just like our teeth. Scratches have been found on the enamel surface of the tooth-like fossils and these tell us how the conodonts used them to slice and crush their food, almost in the same way that we use our teeth. So we now have a much clearer picture of what some early vertebrates were like and why they had hard parts. Some scientists have suggested that they were sluggish creatures, lounging around on the sea floor, sucking up microscopic plankton for food, but conodonts conjure up a picture of active, hunting animals that caught their prey with a complicated and ferocious looking set of sharp teeth. One of our early ancestors was a small but very vicious killer!
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