June 16, 2011

Spinosaurid Fossil Discovered In Australia

A fossil from a species of dinosaur previously believed to exist only in the northern hemisphere has been found in Australia, giving scientists new leads into the history of dinosaurs, reports the AFP news agency.

The 125-million-year-old neck vertebrae of a fossil discovered in Victoria is identical to that of a Baryonyx, a fish-eating dinosaur from the Spinosaurid family, a family of dinosaurs that were thought only to exist north the equator.

The finding suggests that northern and southern hemisphere dinosaurs had much more in common than previously thought. The traditional theory was that these ancient animals could be placed into distinctive, geographically separated groups. Now, this new finding undermines that popular theory, said Dr. Paul Barrett from London's Natural History Museum.

Thomas Rich, a curator for Museum Victoria, said the vertebrae is that of a Spinosaurus and was found near southern Victoria's Cape Otway lighthouse. It belonged to a fairly small (6.6-foot) dinosaur.

A "spine lizard" with a long, narrow snout much like that of a crocodile, the Spinosaurus was known to live in Europe, South America and South Africa, said Rich, but this is the first time its remains had been found in Australia. "The fact that they existed in Australia changes our understanding of the evolution of this group of dinosaurs," he added.

Rich's paper on the discovery, published this week in Biology Letters, states the find also challenges the idea that Australia's fauna was unique in the Early Cretaceous Period. "The same groups of dinosaurs were widespread when the Earth was once a supercontinent," he said.

"When the Earth evolved into separate continents, the various families of dinosaurs had already reached those landmasses, which explains why the same ones have been found in places now far apart from one another," Rich explained.

Dr Barrett told BBC News: "After looking at this specimen and having been forced to re-assess the distribution of spinosaurids, we took a look at other dinosaur groups from Australia, including the Tyrannosaur our team announced last year."

"Taking all this evidence into account, we started to realize that a lot of dinosaur groups we'd thought of as either northern specialists or southern specialists actually had more cosmopolitan distributions," said Barrett.

While it is only a single juvenile vertebrae bone that was found, the team says it displays features that are unmistakably those of a spinosaurid.

It is very similar to the neck bones of the well-known British dinosaur Baryonyx walkeri. Baryonyx was found in southern England, which in Cretaceous times was a lot warmer and covered by lagoons. It had a classic crocodile-like skull with conical teeth suited for catching fish-like prey in the shallow waters.

The team assumes that the Australian version of this specimen pursued a very similar lifestyle. Its Baryonyx-like snout would have been ideal for pulling fish out of the waters that existed in the plains where it was found back in Cretaceous times.

"The evidence is very limited - we'd be the first to admit that, but we're very confident that this Australian specimen belongs to the spinosaurids," Barrett told BBC News. "And because all the other members of this group share the same skull features we're pretty sure this dinosaur behaved in much the same way."

Scientists, based on the one vertebrae found, decided there is not enough of the animal to make a detailed comparison with other spinosaurids.

"For this reason we decided not to name it, nor did we try to shoe-horn it into any existing genus. We hope that future discoveries will tell us much more about the anatomy and relationships of this animal," Barrett concluded.


Image Caption: Baryonyx skeleton at the Natural History Museum in London. Credit: Ripton Scott/Wikipedia (CC BY-SA 2.0) 


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