Credit: J. LÜ

Proc R. Soc. B doi:10.1098/rspb.2009.1603 (2009)

In the early Jurassic period, about 200 million years ago, the most common flying vertebrates were primitive long-tailed pterosaurs. One hundred million years or so later, the more advanced, short-tailed pterodactyloids came to dominate. How the pterodactyloids evolved from the earlier pterosaurs has been a mystery, but the discovery of a fossil (pictured) in China by Junchang Lü of the Chinese Academy of Geological Sciences in Beijing and his collaborators goes some way towards filling in the blanks.

Darwinopterus modularis has the long skull and neck characteristic of pterodactyloids but the rest of the body, including the long tail, is near-identical to that of more primitive forms. The fossil shows the key steps in the evolutionary transition between the two types of organism. It also demonstrates how natural selection acted on groups or 'modules' of characteristics, such as the head and neck, rather than on individual traits.