By Reuters Published: June 7, 2006, 1:12 PM PDT
Fossils from a hitherto unknown species of a 150 million-year-old dwarf dinosaur have been found in northern Germany, scientists said Wednesday.
Initially they suspected that the remains from more than 11 sauropods were from young dinosaurs. But an analysis of their bones showed they were small adults that probably lived on an island during the late Jurassic period.
"It is the first case of island dwarfing proven for sauropod dinosaurs," said Professor Martin Sander of the University of Bonn in Germany.
Sauropods were the largest animals that lived on Earth. With their long necks, massive tails, small heads and stout legs they weighed on average about 20 tons and measured 20 yards in length. The biggest grew to 80 tons and were as long as 40 meters.
By contrast, the new dwarf species, called Europasaurus, was a mere 1 ton and about 6 yards long--about the size of a small rhinoceros or a big buffalo.
"This one is minute but it is still a big animal," said Sander, who reported the finding in the journal Nature.
The bones were discovered in marine beds in northern Germany. During the Jurassic period, sea levels were much higher than today, so much of central Europe was underwater.
Dwarfism is a common phenomenon on islands. The scientists believe the animals' size decreased because they lived in an area where sea levels rose and land masses shrunk.
Another possibility is that they moved as large animals to islands and shrank within a few generations because of limited resources.
Their small leg bones had led scientists to believe they were young dinosaurs, until a technique called bone microstructure revealed they were adults.
Sander and his team, who are one of only four groups worldwide who use the technique to study dinosaurs, took cores from the leg bones to determine the age of the dinosaurs.
"The microstructure of the bone is really well preserved. You can see where the cells were and the blood vessels," he said.
By comparing the size of the bones of the dwarf dinosaurs with their closest ancestors and descendants, the scientists determined how old they were.
The smallest upper leg bone they analyzed was 6.3 inches in length and the biggest 20 inches. Dwarf dinosaurs with 20-inch leg bones were fully grown, but in other species that would have represented a young animal.
Their closest relatives had femurs measuring 1.5 to 2 yards, according to the scientists.