Jeremy Ley, of Ilam School, asks :-

When palaeontologists find the bones of an extinct animal, how do they know how the bones fit together?

Ewan Fordyce, a geologist at the University of Otago, responded.

Some fossils have bones like those in living animals. In these cases we therefore know how the bones of the fossil fit together even if some parts are missing from the fossil. Most fossil penguins from New Zealand are like this - we can reconstruct them easily.

However, many fossils have no close relatives to show how the bones fit. Dinosaurs are like this - they aren't much like living lizards.

So, exactly how do we fit dinosaur bones together? If we study them carefully, we can decide what dinosaur bones did because of their shape. If we know what bones did, we can say what parts they are. Then we can fit them together properly.

Some problem fossils are different from anything living. What did their bones do? Strange "armoured fish" about 400 million years old are known from "armour" plates that have fallen apart. Those plates are preserved well. They are like a perfect jigsaw that can be put together to show what the fish looked like.

The best way to see how bones fit together is to find complete skeletons preserved as if they had just died. This is what I sometimes do.

By the way, if you want to know more about bones or fossils, you could look at the books "Fossil" by P.D. Taylor (Collins 1990) "Skeleton" by S. Parker (Collins 1988). These books have really good pictures. And, if you ever visit Dunedin, you could come to our Geology Department Museum (open 9-5 weekdays) which has the biggest collection of old fossil bones in New Zealand.