The biggest dinosaur in the world has been discovered near the Spanish town of Teruel, Europe's richest site for dinosaur remains, scientists claim.
A fossilised humerus, or forearm, 1.78m (nearly six feet) long, shown to the public for the first time this week, belonged to a giant herbivorous sauropod, whose forearms were tiny compared with the huge size of the rest of its body.
Luis Alcala, the palaeontologist who has led the team investigating the site for the past two years, described the discovery as "exceptional" and "thrilling". He said: "Up to now, the biggest humerus we have found in an animal of these characteristics from the same Cretaceous period was from the Egyptian Paralititan, and that was l.69m long. So we can assume that the dinosaur we have found in Teruel is even taller and longer."
Apart from being the biggest humerus discovered in Europe, the fossil was in an extraordinarily good state of preservation, Mr Alcala said. The find is even more exciting "because of the quantity and diversity of other bones we have recovered," he added.
The gigantic creature that once roamed this part of Europe is thought to be up to 130 million years old. Ribs, breast bones, pelvis, vertebrae and enormous back and front feet have also been found. One fingernail was 40cm long; the smallest rib measures 1.5m. The dimensions suggest the animal could have been up to 35m long and weighed some 50 tons.
A dinosaur this huge is only comparable to the Argentinosaurus, from Argentina, which was considered the heaviest animal that ever walked the earth. Its humerus was 1.81m long. But it was a brachiosaurus, "which is usually more upright, taller and with bigger forearms and shorter legs than the [sauropod], so it was probably shorter," Mr Alcala said.
"We can calculate the overall size by establishing the proportions from bones like the humerus and vertebrae. We know it is enormous, but we can't be more precise yet because we're just starting. It's tremendously exciting."
The site at Riodeva, 43km from Teruel, promises to be a rich mine of dinosaur fossils. Scientists hope to recover more vertebrae, and the creature's tail and head, and are investigating to see whether they have discovered a new species. Luis Sanz, a palaeontologist at Madrid's Autonomous University, said: "If it turns out to be a new species of dinosaur, the find at Riodeva would be even more important."
It used to be thought that giant dinosaurs with huge body mass and weighing dozens of tons needed to live in water. "But it is increasingly evident that these great animals were terrestrial creatures," Mr Sanz said. They are thought to have been gregarious herbivores, voracious for food to sustain their enormous bulk.
The Iberian peninsula at that time is thought to have been tropical or semi-tropical, with well-defined wet and dry seasons, and lush with tree-like ferns, bushes and succulents.
The area around Teruel, in Aragon, has long been of palaeontological interest, with workings that date from the 18th century. Traces of Spain's first dinosaurs were found in the 19th century, and Teruel recently founded a museum-cum-theme park - Dinopolis - to celebrate the creatures.
But the zone of this latest find is "uncultivated". Mr Alcala said: "What we have found ... is just the tip of the iceberg. We will find more remains of this animal and of others belonging to the same herd. We face at least 10 years' work."