April 22, 2009

Paleontologists Uncover Ancestors Of T-Rex In China

An international team of researchers uncovered a treasure trove of dinosaur fossils in China that may help paleontologists better understand the evolution of Tyrannosaurus rex, BBC News reported.

The fossil finds come from a novel tyrannosaur dubbed 'Xiongguanlong baimoensis,' unearthed near the city of Jiayuguan.

Experts believe the bone fossils date from the middle of the Cretaceous period, and could be the missing link tying the familiar big T rex to its much smaller ancestors.

The bones show early signs of the features that became pronounced with later tyrannosaurs.

Two distinct groups of fossils from different parts of the Cretaceous period, which ran from approximately 145 to 65 million years ago, make up the majority of what scientists know about the family of dinosaurs known as tyrannosaurs.

One fossil group dates from an early part of the period known as the Barremian, while the other is from tens of millions of years later. Paleontologists have had trouble tracing the lineage from one group to the other.

Peter Makovicky, associate curator at the Field Museum in Chicago, who helped lead the team that uncovered the fossil, said there is a 40-50 million year gap in which there is very little fossil record.

However, he suggests that X baimoensis was a "nice link" between those two groups and science is slowly filling in that part of the fossil record.

Makovicky and colleagues believe that X baimoensis is a "phylogenetic, morphological, and temporal link" between the two distinct groups of tyrannosaurs.

They wrote in Royal Society's journal Proceedings B, that the fossil has some hallmarks of large tyrannosaurs such as a boxy skull, reinforced temple bones to support large jaw muscles, modified front nipping teeth and a stronger spine to support a large head.

Interestingly, it also shows features absent from older tyrannosaurs, such as a long thin snout.

Two other sets of dinosaur fossils are also featured in the same edition of Proceedings B.

Many of the paleontologists who found the tyrannosaur wrote of another discovery in China, as samples found in the Yujingzi Basin came from a dinosaur that resembled the modern ostrich.

They wrote that while many of these ornithomimosaurs have been uncovered in the past, analysis of the bones of the new species, dubbed Beishanlong grandis, suggest it was one of the largest at almost 20 ft tall and weighing about 1380 lbs.

The researchers were funded by the US National Science Foundation, the National Science Foundation of China, and a Grainger Foundation grant from The Field Museum, and were joined in the field by students and post-docs from their institutions.


Image 1: Excavation at the holotype locality for Beishanlong in 2006. Photo credit: M. Ellison.

Image 2: Silhouettes of body reconstructions for Xiongguanlong (left) and Beishanlong (right) with the recovered parts of the skeletons shown. A six-foot human silhouette is included for scale. Illustration credit: M. Donnelly/The Field Museum.

Image 3: Reconstructed body silhouettes of three tyrannosaurs, showing where Xiongguanlong falls in the spectrum of body sizes in this lineage. Dilong on the left is 125 million years old and the smallest known tyrannosaur. Xiongguanlong, shown in grey, is much larger, but is still dwarfed by T. rex, shown on the right. "Although impressive by today's standards, Xiongguanlong was still a fly weight predator compared to its heavy-weight relatives such as T. rex" says Peter Makovicky, Curator of Dinosaurs at The Field Museum, and corresponding author on the study of Xiongguanlong. Illustration credit: M. Donnelly/The Field Museum.


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