A pygmy dinosaur many times smaller than its giant relatives has been found by a fossil hunter searching a stone quarry in Germany. It is the first time scientists have found evidence of dwarfism in dinosaurs, which could have evolved in response to a shortage of food on the island where they lived 150 million years ago.
When the bones were first unearthed in 1998 it was thought they belonged to juvenile sauropods - the biggest animals to walk on land - but a new analysis shows they were, in fact, fully grown adults.
Sauropod dinosaurs such as brachiosaurus grew up to 45 metres (150ft) long and weighed 80 tons. Their diminutive relatives, which were found in a quarry in Lower Saxony, stopped growing at 6mand weighed less than a ton, which is more than 50 times smaller than their larger cousins.
Martin Sander of the University of Bonn and Octavio Mateus of Museo da Lourinha in Lisbon said that a microscopic analysis of the small dinosaur's bones, published in the journal Nature, has confirmed that they were adults rather than juveniles.
"We really have found a dwarf dinosaur that lies between giants. All of its relatives are really huge," Dr Mateus said yesterday. The part of Europe where the bones were unearthed was largely submerged by the sea 150 million years ago, with the exception of a large island where prehistoric life had remained isolated for millions of years. "Although the dinosaurs had lived on the island for several million years, dwarfism could have occurred relatively rapidly, within about 20,000 years or so," he said.
There are several examples of large species of animals becoming smaller when they live in isolation . Deer introduced to the Shetland islands have evolved into dwarf animals, the remains of pygmy elephants have been found on Mediterranean islands and the bones of dwarf mammoths have been found on Wrangel Island in Siberia.
Even humans are believed to have undergone island dwarfism to produce the controversial "hobbits" that lived on the Indonesian island of Flores as recently as 12,000 years ago.
"This island situation may well be the reason why pygmy dinosaurs evolved. When the sea rose, flooding more land, food resources became scarce," said Niles Knötschke of the Dinopark in Münchehagen, and a member of the research team.
"The result was enormous pressure to evolve. Smaller animals which needed less food had better chances of survival," Dr Mateus said.
The species has been named Europasaurus holgeri in honour of its discoverer, Holger Luedtke, an amateur palaeontologist who was searching a quarry near Oker near the Harz Mountains in northern Germany. "Holger found them in the quarry when he was looking for other fossils. He discovered them almost by accident," Dr Mateus said.
The quarry at Harz has already revealed a menagerie of unusual extinct creatures, such as flying dinosaurs, crocodiles, tortoises and the footprints of a dangerous carnivorous dinosaur that has yet to be identified.