Palaeontologists in Spain have discovered the remains of a strange dinosaur with a hump that they believe is the forerunner of flesh-eating leviathans which once ruled the planet.
The fossil was uncovered in the Las Hoyas formation in central Spain's Cuenca province, a treasure trove of finds that date to the Lower Cretaceous period of between 120 and 150 million years ago.
The nearly-complete skeleton is as exquisite as the dinosaur is "bizarre," Fernando Escaso of the Autonomous University of Madrid, told AFP by phone.
"This dinosaur is very remarkable," Ecaso said.
"It is a unique specimen. It is the most complete dinosaur ever found in the Iberian peninsula and is a new species of theropod," a carnivore that moved on two rear limbs.
Six metres (20 feet) long from snout to tailtip, the dinosaur is the earliest member ever found of a branch of Carcharodontosauria, the largest predatory dinos that ever lived and which until now were thought to be confined to southern continents.
The lineage expanded hugely over the aeons, both in size and number of species.
Its numbers include Giganotosaurus, estimated up to 14.5m (47 feet) long, and Carcharodontosaurus, up to 13 metres (44 feet) long, and each weighing some seven or eight tonnes.
The new find has jaws and small, clawed forelimbs that bear a resemblance to the Tyrannosaurus rex which belongs to a different dinosaur family.
But all similarities end with the spine, which is astonishingly curved and has a small hump, Ecaso said.
"It is the first time we have ever seen a structure like this on the spine of a dinosaur, although it is common on some animals today, such as cows," Escaso said.
"At the moment, the function of this structure is unclear. We believe that the animal was not diseased because the spine shows no sign of being cracked or broken, we think it is a feature of this species. One hypothesis is that it was a reservoir of fat."
The new species has been named Concavenator corcovatus, from "Conca," the Latin word for Cuenca; "venator," for hunter; and "corcovatus," or hump-backed.
The study is published on Thursday by the British science journal Nature.
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