Bird like dinosaurs challenge evolutionary trend
chinese researchers have unearthed a massive dinosaur fossil from the Iren Dabasu Formation of Nei Mongol in China.According to the researchers, the giant dinosaur belongs to a family of bird-like dinosaursoviraptors. The discovery is set to challenge the evolutionary theory described earlier.
Reason: the oviraptors rarely exceeded 40 kg in body weight while the latest discovery dating back to 70 million years weighs around 1,400 kg and was eight metres long. As meat-eating dinosaurs like tyrannosaurus got smaller, they became more bird-like. The discovery was published in Nature (online June 13, 2007).
The fossil, according to the researchers, had many characteristics similar to oviraptors but many dissimilar too.The researchers have put the fossil in the same family as oviraptors but named it Gigantoraptor because of its huge size (300 times the size of an oviraptor).The new species was named Gigantoraptor erlianensis. The specific name -- erlianensis -- came from the Erlian basin where the holotype was collected.
The fossil was discovered in 2005 but was first considered to be of a tyrannosaurus because of its size. But later studies found that the fossil had a beak instead of teeth. The study describes that the dinosaur also had sharp claws. But there is no evidence that Gigantoraptor had feathers, a characteristic that sets it apart from its oviraptor cousin, apart from the body size and weight. Its lower jaw was also intermediate in shape between basal oviraptors and highly specialised oviraptors. That is why in the evolutionary tree, Gigantoraptor has been put at the base of the family Oviraptoridae to which oviraptors belonged.
The histological analysis suggests that the Gigantoraptor probably died during its eleventh year of adult life. This suggests that Gigantoraptor has an accelerated growth rate faster than most theropods (a group to which oviraptors belong)similar to the growth strategy seen in most giant dinosaurs.
Experts say the finding shows that diversity among dinosaurs is much greater than scientists previously believed. A 2006 study in Proceedings of the National Academy of Sciences estimated dinosaur diversity at around 1,850 of which about 527 dinosaur genera have been identified with certainty and about 70 per cent remain undiscovered. Some even predicted that about 3,400 dinosaur genera existed, including many not preserved as fossils.