Monday, November 16, 2009

Skeletons Dancing On The Head of a Pin

Morphological criteria for recognising homology in isolated skeletal elements: comparison of traditional and morphometric approaches in conodonts. 2009. D. Jones, et al. Palaeontology, published Online: Nov 13.

Four different types of conodont teeth from different species. Photo: U of Leicester
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. 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.

Ancient marine rocks are often packed with thousands of scattered microscopic 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!

To help sort out the problem scientists studied material from a 425 million year old rock deposit in Ontario, Canada 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.

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.