Reconstructing ancient fossils

Reconstructing ancient fossils from thousands of jumbled up pieces can be fiendishly challenging. A new study pitting academic expertise against a computer in recreating a 425 million-year old jigsaw puzzle has discovered that there is no substitute for wisdom born out of experience.

The investigation, based on fossil teeth from extinct vertebrates, found that the most specialised experts provided the most reliable identifications.

'Being a palaeontologist can be fun, but sometimes it isn't easy,' said University of Leicester (U-L) researcher Mark Purnell.

'Take vertebrates, the group to which we belong. When a vertebrate animal dies, whether it's a fish, a sabre-tooth cat or a dinosaur, the flesh rots away and the bones of the skeleton are usually scattered before being fossilised.'

'In order to interpret them correctly, the palaeontologist must piece them back together, or at least work out which bits are which,' said Purnell.

'This is difficult enough when you have modern relatives for comparison; but what if there's nothing alive today that's remotely like the extinct animal you need to analyse? It's exactly like doing a jigsaw puzzle without a picture,' added Purnell

This is what faces palaeontologists who study conodonts. Conodonts are extinct chordates (a group of animals that includes the vertebrates) resembling eels.

'Earth's oceans teemed with conodonts for 300 million years; they were the most common vertebrates around, and they were the first to evolve teeth,' said David Jones, lead study author at the U-L.

'In fact the conodont skeleton was all teeth: a basket of hacksaw-shaped blades which was extended out of the mouth to grab prey, behind which lay pairs of slicing blades and crushing teeth - a set of gnashers straight out of the movie 'Alien',' said Jones.

Ancient marine rocks are often packed with hundreds or thousands of scattered conodont teeth, with many species jumbled up together.

'To make matters worse, within any one animal, teeth from different parts of the skeleton looked almost identical! Now we have a jigsaw puzzle with no picture, where each piece could go in different places. But just so it's not too easy, conodont teeth are also microscopic,' said Purnell, geologist at U-L.

Jones and Purnell teamed-up with Peter von Bitter from the Royal Ontario Museum, Canada, to bring sophisticated statistical techniques to bear on solving this skeletal jigsaw.

They used material from a 425 million-year-old-rock deposit in Ontario, which unlike almost all other deposits in the world, preserves both scattered teeth and complete skeletons of conodonts.

This material allowed them to compare the success rate of experts in placing the teeth in the correct positions within the skeleton, with the success rate of computer-based methods, says a U-L release.
So how do the experts stack up against the machines?


'Pretty well,' says Jones. 'This is reassuring for palaeontologists! But the computer-based approach did at least as well and was also consistent; experts disagreed amongst themselves, and less experienced palaeontologists, not surprisingly, made more mistakes.'

The new study was published in the latest issue of Palaeontology.