Giant Bird-like Dinosaur Revealed From Inner Mongolia (6/24/2007)

Gigantoraptor Erlianensis - Image Credit: The Chinese Academy of Sciences

Teaming up with local scholars, CAS paleontologists recently discovered a giant bird-like dinosaur from Erlian, one of the world-famous graveyards of "terrible lizards" in Inner Mongolia. The new findings, named Gigantoraptor erlianensis, is a new but bird-like dinosaur and the fourth new dinosaur taxon recovered from the basin in recent years. Researchers say that its discovery will greatly enrich our knowledge on the complexity in the evolutionary process of the bird's origin.

As reported at the June 14 issue of the prestigious British journal Nature, the dinosaur's fossil remains were brought to light by XU Xing with the CAS Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and his co-workers in Inner Mongolia from an 80 million-year-old late Cretaceous formation in Erlian Basin, from which, about 80 years ago, a US expedition had discovered a bonanza of vertebrate fossils, including the earliest identified dinosaur eggs.

Scientists speculate that the Gigantoraptor was about eight meters long, more than five meters tall and weighed not less than 1.4 tons. Although on a par with the formidable tyrannosaur in size, it was surprisingly found to be more closely related to the oviraptorosaur (egg-eating dinosaur), which was a close relative of primitive birds but in relatively small sizes, mostly weighed about several kilograms.

Although no direct evidence that the Gigantoraptor was feathered, but based on its close relationship to other feathered species, scientists inferred as it was. If this was true, it would be a rare sight in the whole evolutionary history of the living kingdom to see such a mammoth animal wholly covered by feather. Just like its cousin, the oviraptorosaurs, there were no teeth within its mouth. Instead, it developed a huge beak. Only one thing is uncertain: scientists cannot definitely confirm whether its beak was used to cut off herbal stems, feeding on a small-sized prey or press an egg into pieces.

Many up-to-date technologies have been used in the research of the fossil specimen, including slicing through a bone to analyze its microscopic characteristics. Scientists discover the individual was a sub-adult and about 11 years old when it was dead. Based on this, they estimate an adult should be far more than 1.4 tons in weight and the species adopted an accelerated tempo in its growth strategy, which, scientists believe, might be higher than that of some of its close relatives: the coelurosaurs. When the CT scanning technique was applied to the examination of the inner structure of its vertebrae, researchers find there is a sponge-like texture in it, sharing some similarities with that in the body of its herbivorous sauropod cousins.

There are many distinctive traits in the new species never seen before in the fossilized remains of other dinosaurs. Scientists remain puzzled after pondering over some grotesque cavities in its vertebrae because they cannot find out their possible functions. Another perplexity lies in the eccentric proportion of its hind limbs. As usual, when a dinosaur's size is in increase, its four limbs should be growing more robust and their ends would be shorter. On contrary, the newly found species has more slender hind legs and its shanks are so long that researchers cannot but guess it must be versed in galloping in comparison with other quadrupeds.

The most interesting trait shown by the specimen lies in its many bird-like anatomic features. Past studies suggested bird-like features had long been thought to be accompanied by a decrease in size, meaning the smaller the species, the more bird-like it is likely to be and vice versa, so that a dinosaur's stature is positively proportional to the deepness of its avian characteristics. It is widely recognized that all bird-like dinosaurs are in small sizes. The size was smaller, it would have more avian distinctions while the size became bigger, its avian attributes would disappear in many cases. To their surprise, the scientists find the new species should be an exception because it seems to have more bird-like features than most of other small-sized egg-eating cousins. This fact proves that, in the course of avian evolution, there must have many different evolutionary patterns and the hidden mechanisms behind the evolutionary events would not be in a single mode. Such a situation makes the matter seems more complicated.

Further research is still necessary to reveal the dietary composition of the new species. "Its small head and long neck indicate it would have been a vegetarian, however, it belongs to a family of carnivores," Xu said.

Before the discovery of the Gigantoraptor, the largest feathered animal was Stirton's Thunder Bird (Dromornis stirtoni), that weighed about 500 kilograms and lived in today's Australia 6-8 million years ago. But the Gigantoraptor was broken the record, being three times as heavy as the Thunder Bird.

In recent years, Chinese scholars have made a series of distinguished results on the avian origin, including the discovery of feathered dinosaur fossils from early Cretaceous period in Western Liaoning Province. The latest Inner Mongolian finding adds new materials for thought, deepening our understanding of the transitional process from reptiles to winged birds. In addition to his coworkers at the Longhao Institute of Geology and Paleontology in Inner Mongolia, Prof. Xu Xing is one of pioneers in the current research drive as he has expanded the research scope from the world-famous Jehol Biota in Liaoning Province to the Jurassic strata in Xinjiang and later Cretaceous formations in Inner Mongolia. His work is now being supported by the CAS and National Foundation for Natural Sciences of China.

Note: This story has been adapted from a news release issued by The Chinese Academy of Sciences

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