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The hunchback of central Spain

New dinosaur species has a hump plus possible featherlike structures on its arms

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4:39pm, September 8, 2010
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A newly described carnivorous dinosaur species has a strikingly unusual hump on its back and hints of featherlike appendages on its arms. The 125 million-year-old fossil from central Spain suggests that feathers evolved in more primitive dinosaurs than previously thought, researchers say.

Scientists found the nearly complete skeleton of Concavenator corcovatus, which means “the hunchback hunter from Cuenca,” at a fossil site called Las Hoyas, in Cuenca, Spain, in 2003. The fossil was exquisitely preserved in the dense limestone, which had impressions of the dino’s scales. After seven years of painstaking removal, vertebrate paleontologist Francisco Ortega of the Universidad Nacional de Educación a Distancia in Madrid and his colleagues have published the first description of the animal in the Sept. 9 Nature. 

Concavenator belongs to a family of dinosaurs known as Carcharodontosauria. These carnivores walked on hind legs, had three main fingers at the end of each stubby arm and ripped through flesh with razorlike teeth.

But the 20-foot-long Concavenator fossil sports two features that have never been seen in its family. Two of the dinosaur’s vertebrae are longer than the rest, indicating that it had a tall hump on its back that wasn’t very long. Among other dinos, humps are fairly common but usually span more vertebrae, as in the sail-shaped hump of the spinosaurus.

“People have discovered tall-spined European early cretaceous carnivorous dinosaur vertebrae since the middle of the 1800s, but … we didn’t have complete skeletons” that showed where the hump was positioned, says vertebrate paleontologist Thomas Holtz Jr. of the University of Maryland in College Park, who was not involved in the study.

Concavenator also has bumps on its forearm bones that look a lot like quill knobs seen on the wing bones of modern birds. Quill knobs are attachment points in the bone for ligaments that support a bird’s flight feathers. This could mean that Concavenator had featherlike structures on its arms.

Signs of feathers have been found in dinosaur fossils before, says paleontologist Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County. But such evidence has been seen mainly in dinosaurs that are more closely related to birds.

“This is really pushing back, at least from the genealogic perspective, the origin of feathers,” Chiappe says.

And if such a primitive dinosaur was feathered, he says, its many descendants were probably feathered as well, which could mean “by inference, maybe a third of all dinosaurs that we know of were feathered.”

It’s unclear why feathers or humps might have evolved in dinosaurs, but these traits may have been used for display in mating or for regulating body heat, scientists say.

“The real question is whether or not these are real traces of feathers or something else,” Holtz says. “If these do turn out to be feathery arms, it shows that you can have dinosaurs that had scales over large parts of the body, but still had feathers in some isolated spots. That wasn’t really known before.”

The new discovery also helps extend the range in which carcharodontosaurs were known to live. Most known fossils from this group have been found in the southern continents from 90 million to 100 million years ago. But Concavenator was found farther north and lived about 125 million years ago.

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