The shark-toothed dinosaur with a ‘fin’ on its back

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Dinosaur bodies are covered in all sorts of spikes, horns, plates that were used for defence, combat and identification. But sometimes, these body parts are so bizarre that their purpose is a mystery.  The latest in these strange projections belongs to Concavenator, a new giant predator with two spikes sticking up from the vertebrae just in front of its hips. They would probably have given the dinosaur a strange hump on its back.

Concavenator’s  skeleton – virtually complete and beautifully preserved – was discovered by Francisco Ortega in Spain’s Las Hoyas formation. At six metres long, it dwarfed most of the other bones recovered from the area but it was still a runt within its own family tree. Concavenator was a primitive member of the carcharodontosaurids, a group of “shark-toothed” predators, many of which were larger than Tyrannosaurus. And while it shared the basic body shape of its relatives, two of its features stand out.

The most obvious ones are the bizarre spikes on its hips. Back when the animal was flesh as well as bone, these spikes would have formed a kind of hump. “The most plausible role for this structure is that of a deposit of fat,” says Ortega. It might be like the hump of modern animals like zebu cattle, but these humps have no internal bony supports. Alternatively, a structure that striking could allow individuals to communicate with one another. The spikes could also have supported a fold of skin that helped Concavenator to keep cool. “For the moment, we can consider that all these options are reasonable interpretations, but they still remain in the realm of speculation,” says Ortega, who has no favourites among the three hypotheses.

Concavenator’s arms are potentially even more interesting. Its forearms have a row of small bumps and Ortega thinks that these are quill knobs, bony lumps that act as attachment points for feathers. The primary feathers of modern birds connect to their forearms via quill knobs. Similar bumps were discovered on VelociraptorSimilar bumps were discovered on Velociraptor a few years back, providing hard evidence that this small dinosaur has feathers. Whether Concavenator had feathers is a different matter. The things that sprouted from the knobs were probably short, rigid filaments, only distantly related to the full-blown feathers of birds and other smaller dinosaurs.

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