The six-meter-long theropod (Concavenator corcovatus) hunted in modern-day Spain some 125 million years ago.
Unlike a camel's fatty hump, this carnivorous dinosaur's bump was made of solid bone. And it was hardly a subtle feature—the eleventh and twelfth vertebrae towered five times taller than the top of the rest of the vertebrae's centra (central portions).
The fossilized skeleton was "almost complete and exquisitely preserved," the researchers noted in the description, published online September 8 in Nature (Scientific American is part of Nature Publishing Group). It was so well conserved over the eons, that the team, led by Francisco Ortega, of the Universidad Nacional de Educacíon a Distancia in Madrid, think that they also found evidence of follicles on the animal's forearm—an indication that it might have sported at least a few quill feathers or other protruding elements.
The researchers didn't speculate what function the hump might have served. Other dinosaurs had striking spine-based spikes, such as Stegosaurus, that might have been used for display, fat storage or temperature control. "But the abrupt, tall…singular structure of Concavenator has no analogous structures" among other dinosaurs, the researchers noted.
Listen to a podcast that features an interview with Nature editor Henry Gee on the finding.
Image of Concavenator corcovatus courtesy of Raul Martin