Tuesday, 8 January 2013

Pulling Hen's Teeth

Pulling hen's teeth describes a task that is futile or difficult in the extreme. Hens, or for that matter all species of bird, do not have teeth and so any task is, in essence, over before it's begun. This is only the case with modern avians, however. Try the same trick with earlier members of the group and you would yield rather better results. The earliest known species of bird, Archaeopteryx lithographica, had a beak lined with tiny, pointed teeth.

The teeth of Sulcavis geeorum. The image
is a close u of the complete skeleton
This was noted by Sir Richard Owen, who purchased the fossil for the Natural History Museum, London in the 1860s. Since then, it has been thought that birds slowly lost their teeth as the group diversified, leading to the toothless species seen in the fossil record a few million years later and in their descendants today.

Yet a fossil discovery from China is shows that some groups actually held onto their dentures for tens of millions of years after Archaeopteryx.

Sulcavis geeorum was unearthed in 121 million year rocks in the Liaoning Province of China, a region famous for its well preserved fossils of complete Cretaceous ecosystems. Part of a group of birds known as the enantiornithines, it had distinct teeth which showed up as black striations in the fossilised jaw. Sulcavis, and possibly its close relatives, had kept their teeth in order to deal with a completely new diet of meat and hard-shelled crustaceans.

A reconstruction of the 121 million year old
toothed bird Sulcavis geeorum from Liaoning, China
Grooves on the inside of the structures gave them greater strength which allowed them to feed upon the hardier food items in their diet. 'While other birds were losing their teeth, enantiornithines were evolving new morphologies and dental specializations. We still don't understand why enantiornithines were so successful in the Cretaceous but then died out – maybe differences in diet played a part, said Jingmai O'Connor, the lead author of the study into Sulcavis geeorum.

Today, birds are incredibly diverse and some of the most beautiful creatures on Earth. Yet their early evolutionary history is poorly understood, partially due to a lack of fossils, partially due to the incomplete nature of those fossils. Fossils of giant, powerful predatory avians, the phosphorhacids, show that, at one point, birds ruled the planet. Yet their long and rich story started with the strange, early forms of Sulcavis and Archaeopteryx.