New flying reptile clues to rapid evolution

14 October 2009

A new species of ancient flying reptile shows evidence that evolution didn't always happen in small gradual steps, scientists report today in the Proceedings of the Royal Society B: Biological Sciences.

Illustration of Darwinopterus hunting a small feathered dinosaur (Anchiornis)

Illustration of Darwinopterus hunting a small feathered dinosaur (Anchiornis) © Mark Witton, University of Portsmouth

An international group of researchers from the University of Leicester (UK), and the Geological Institute, Beijing (China) have identified and named the new pterosaur (also known as pterodactyls) Darwinopterus after Charles Darwin.

The crow-sized Darwinopterus lived about 160 million years ago in between when two distinct groups of pterosaurs lived (the oldest pterosaurs lived more than 200 million years ago and the most recent, 65 million years ago).

More than 20 skeleton specimens, some complete, show that Darwinopterus had characteristics of both pterosaur groups, rather than having characteristics that are in-between as scientists had expected. Darwinopterus had advanced features in its head and neck, like you see in the more recent group of pterosaurs, but it also had primitive body structures, wings and tail, like the older pterosaurs.

Modular evolution

This means the front end of Darwinopterus evolved at a much faster rate and separately from its back end, rather than a gradual change of separate structures. This fits a controversial theory called 'modular evolution' where functionally integrated groups of structures evolve together at a faster rate than structures elsewhere in the body.

Arrow shows evolution direction from primitive long-tailed pterosaur, top, to advanced short-tailed

Arrow shows direction of evolution from primitive long-tailed pterosaur at top to advanced short-tailed pterosaur at bottom with Darwinopterus in the middle. © Dave Unwin

‘This very interesting pterosaur provides a dramatically clear demonstration that evolution apparently did not always take place with gradual changes in characters happening at the same speed throughout the organism,’ says Natural History Museum dinosaur expert Dr Angela Milner.

'This is a somewhat controversial hypothesis and Darwinopterus illustrates that sets of integrated features could evolve at very different rates. It sits right in the middle of a big evolutionary gap between the two distinct and well known groups of pterosaurs, not by being part-way between them anatomically as might be predicted, but by having a remarkably advanced front end (the head and neck) attached to a primitive body and wings.'

The fossil record

Dr David Unwin, part of the research team concludes, 'Frustratingly, these events, which are responsible for much of the variety of life that we see all around us, are only rarely recorded by fossils. Darwin was acutely aware of this, as he noted in the Origin of species, and hoped that one day fossils would help to fill these gaps. Darwinopterus is a small but important step in that direction.'

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