Pterosaur discovery points to modular evolution

Posted by Emma Woollacott

A new type of flying reptile that's been discovered provides the first clear evidence of a controversial type of evolution.

Pterodactyls, which ruled the skies around 250 million years ago, fell into two types: primitive long-tailed forms and their descendants, short-tailed pterosaurs, some of which were enormous. The new pterosaur, Darwinopterus, fits exactly in the middle of the gap between the two.

A group of researchers from the University of Leicester and the Geological Institute of Beijing examined more than 20 fossil skeletons of Darwinopterus, some complete, found earlier this year in north-east China.

The long jaws, sharp-pointed teeth and flexible neck of the crow-sized creature suggest that it might have been hawk-like.

David Unwin of the University of Leicester's School of Museum Studies said that researchers had always expected a gap-filler with typically intermediate features such as a moderately elongate tail. "But the strange thing about Darwinopterus is that it has a head and neck just like that of advanced pterosaurs, while the rest of the skeleton, including a very long tail, is identical to that of primitive forms," he said.

This imples that evolution from one type of pterosaur to the other happened quickly, and that whole groups of features - modules - forming important structures such as the skull, the neck, or the tail, seem to have evolved together.

"The head and neck evolved first, followed later by the body, tail, wings and legs," says Unwin. "It seems that natural selection was acting on and changing entire modules and not, as would normally be expected, just on single features such as the shape of the snout, or the form of a tooth. This supports the controversial idea of a relatively rapid 'modular' form of evolution."
 
The team warns that much more work is needed to substantiate this theory. But it might help explain many other cases of rapid large scale evolution, such as the extraordinary evolutionary radiation of mammals following the extinction of dinosaurs.

Details appear in the Proceedings of the Royal Society B: Biological Sciences.