But now it turns out that these small animals were a tribe of fully adult pygmy dinosaurs, a new species which was about 20 feet long.
P. Martin Sander, a Bonn University paleontologist, took thin slices of the fossil bones and examined them under the microscope to study their fully formed blood vessels and their centers of development -- known as their lines of arrested growth. Those lines are like tree rings, he said, providing the best evidence of the dinosaurs' age.More details over here.
He found that the small creatures had in fact stopped growing, were fully adult, and represented an entirely new and unknown species of dwarf dinosaurs.
Among their giant cousins, those dwarfs were small indeed -- 20 feet long at most, and weighing about a ton. Their closest relatives, the brachiosaurs, grew up to 150 feet long and weighed nearly 90 tons