Tuesday, January 5, 2010

First-known venomous dinosaur found

A feathered predator that lived 125 million years ago has been revealed as the first-known venomous dinosaur, which paralysed its prey with poison in a similar way to some snakes.

Sinornithosaurus millenii, a dinosaur about the size of a turkey, had grooved fangs for channelling venom and a pocket in the upper jaw that probably held venom glands, scientists have discovered.

The anatomy is similar to that of “rear-fanged” snakes such as the boomslang, which do not inject poison directly through front fangs but funnel it along grooved teeth as they pierce the skin of their prey.

The new research offers the strongest evidence yet for the evolution of venom in dinosaurs. While the idea has long intrigued scientists — the species Dilophosaurus was portrayed in the film Jurassic Park as spitting venom — there were until recently no fossil records to support it.

In 2000 a grooved tooth from a theropod dinosaur was discovered in Mexico, indicating that it may have funnelled venom. Much more extensive evidence for this has now been found in Sinornithosaurus. Scientists from the University of Kansas and Northeastern University, who conducted the research, said it was likely that the dinosaur used its venom not to kill but to immobilise its prey so it became easier to dispatch. This is also how most modern-day rear-fanged snakes and lizards hunt.

David Burnham, of the University of Kansas, said: “You wouldn’t have seen it coming. It would have swooped down behind you from a low-hanging tree branch and attacked from the back. Once the teeth were embedded in your skin the venom could seep into the wound.

“The prey would rapidly go into shock but it would still be living, and it might have seen itself being slowly devoured by this raptor.”

His colleague Larry Martin said: “When we were looking at Sinornithosaurus, we realised its teeth were unusual. Then we began to look at the whole structure of the teeth and jaw.

“At that point, we realised it was similar to modern-day snakes. This thing is a venomous bird for all intents and purposes. It was a real shock to us.” Sinornithosaurus, which was first discovered in China in 1999, was a predator closely related to other species such as Velociraptor and Microraptor gui — which is thought to have used feathered “wings” to glide.

Other details of its anatomy, described in the journal Proceedings of the National Academy of Sciences, suggest its main prey may have been smaller feathered dinosaurs or primitive birds. The scientists wrote in their paper: “We believe that Sinornithosaurus was a venomous predator that fed on birds by using its long fangs to penetrate through the plumage and into the skin, and the toxins would induce shock and permit the victim to be subdued rapidly.”

Dr Martin said: “This is an animal about the size of a turkey. It’s a specialised predator of small dinosaurs and birds. It was almost certainly feathered. It’s a very close relative of the four-winged glider called Microraptor.

The team believes that other bird-like dinosaurs may also have had venomous bites. The researchers are now studying Microraptor fossils to determine whether it had a similar venom-delivery system.

The findings are a significant addition to evolutionary theory. Contrary to popular belief, dinosaurs were not closely related to modern reptiles, which means that the grooved-tooth adaptation must have evolved independently in snakes and Sinornithosaurus.

This is a fine example of convergent evolution, in which natural selection guides the evolution of similar functional traits in species that are not closely related. It often finds similar solutions to challenges that occur repeatedly in the natural world — in this case, how to subdue prey.

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