Oldest-known Tyrannosaur Reported By American Museum Of Natural History Paleontologist

by AMNH on


Guanlong wucaii

Credit: IVPP

An American Museum of Natural History scientist and his colleagues have described the oldest-known tyrannosaur, a new presumably predatory dinosaur that sported a strange combination of features, including a large, fragile crest on its head that would have made the animal attractive to mates but vulnerable in a fight. The team has named the new dinosaur Guanlong wucaii, with the generic name derived from the Mandarin word for "crowned dragon" and the specific name referring to the rich colors of the rocks in the Junggar Basin in northwestern China where the specimens were found. The nine-foot-long specimen (and another skeleton of the same animal also described in the new research paper) is from the Late Jurassic Period and is about 160 million years old. Most tyrannosaur specimens, except a few fragments, date only to the later period in geologic timethe Cretaceous. None of the previously discovered tyrannosaurs are as old as G. wucaii, including a 130-million-year-old, relatively primitive, feathered tyrannosaur, Dilong paradoxus, reported by Museum scientists and colleagues in 2004. G. wucaii now displaces D. paradoxus as the most primitive tyrannosaur found to date. The wide variety of features found in G. wucaii as well as in coelurosaurs, a larger, related group of bird-like theropod dinosaurs to which it belongs, suggests that traits in these animals were modified dramatically as theropod dinosaurs changed over time.

The G. wucaii specimen that will be used as the baseline for scientists studying it in the future was a 12-year-old adult when it died. It possibly was trampled by the second specimen, a 6-year-old juvenile, described in the new research. The crest on G. wucaii's head was filled with air sacs and is comparable to the exaggerated ornamental features found on some living birds such as cassowaries and hornbills. The crest was about one and a half millimeters thick, about as thick as a tortilla, and it measured about two and a half inches high.

The new finding is described in the journal Nature by Mark A. Norell, Curator in the Division of Paleontology at the American Museum of Natural History; Xing Xu, Chengkai Jia, and Qi Zhao of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing; James M. Clark of George Washington University; Catherine A. Forster of Stony Brook University; Gregory M. Erickson of Florida State University; and David A. Eberth of the Royal Tyrrell Museum (Drumheller, Alberta, Canada). Dr. Xu is also a research fellow at the American Museum of Natural History, and Drs. Clark, Forster, and Erickson are also research associates at the Museum.

"The discovery of this basal tyrannosaur is giving us a much broader picture of the diversity in this group and its ancestors, and is suggesting new interpretations for ornamental structures in these animals and others," Dr. Norell said.

Guanlong wucaii fossil

Credit: IVPP

The skeleton of G. wucaii resembles those of more derived, or advanced, tyrannosaurs, except that the new dinosaur had three fingers (one more than is found in advanced tyrannosaurs) and is much smaller than the advanced tyrannosaurs that followed, including, of course, Tyrannosaurus rex. The front teeth and other skull and pelvic features of G. wucaii suggest that it was an intermediate animal in the evolutionary route between primitive coelurosaurs and tyrannosaurs. A mathematical analysis of the relationships among these dinosaur groups and their close relations confirms that G. wucaii is the most primitive tyrannosaur known, or is the first branch on the tyrannosaur family tree. 

"Guanlong shows us how the small coelurosaurian ancestors of tyrannosaurs took the first step that led to the giant T. rex almost 100 million years later," Dr. Clark said.

The crest on G. wucaii is comparable to the exaggerated ornamentation of a peacock's tail or the large horns on Irish elks. Among modern animals from beetles to bison, horns are almost always used to attract mates, compete with rivals, or allow animals of the same species to recognize each other. The crest on G. wucaii is too thin to have provided much protection. So the crest on G. wucaiilikely was used for display or mate recognition, not defense. 

"On one hand, Guanlong looks like just what paleontologists have been expecting for a primitive tyrannosaur," said Dr. Xu. "On the other hand, no one expected that a tyrannosaur would bear a crest like this, large and delicate. Even after so many great discoveries, we have to say there is still a lot we don't know about dinosaurs. They are really a diverse group of animals."

The work on G. wucaii was funded by the Special Funds for Major State Basic Research Projects of China, the National Natural Science Foundation of China, the National Geographic Society, the Chinese Academy of Sciences, the National Science Foundation of the USA, and the American Museum of Natural History.

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