January 25, 2011

First Single-clawed Dinosaur Unearthed In China

An international team of paleontologists has unearthed a new species of dinosaur in Inner Mongolia, China. 

The dinosaur, named Linhenykus monodactylus after the nearby city of Linhe, was a miniature, single-clawed theropod, and was likely an early relative of the infamous Tyrannosaurus Rex, the researchers said.

It is the only creature known to have just one finger, and would have been about three feet tall with the approximate weight of a parrot.

The new species belongs to the Alvarezsauroidea, a branch of the carnivorous dinosaur group Theropoda, which gave rise to modern birds and includes such famous dinosaurs as T. Rex and Velociraptor.

Most theropods had three fingers per hand, but this one had only a single large claw that was likely used for digging into insect nests, the researchers said.

"Non-avian theropods start with five fingers but evolved to have only three fingers in later forms," said Michael Pittman of the Department of Earth Sciences at University College London, co-author of the study.

"Tyrannosaurs were unusual in having just two fingers but the one-fingered Linhenykus shows how extensive and complex theropod hand modifications really were."

Linhenykus lived with closely-related and similarly-sized theropod dinosaurs, but the specializations of its skeleton may reflect differences in behavior or foraging strategy, the researchers said.  

It also lived alongside small mammals, lizards, clubbed dinosaurs (ankylosaurs) and horned dinosaurs (ceratopsians).

Scientists are not entirely sure why Linhenykus evolved to no longer have its other two digits.

"Their disappearance may simply reflect the fact that they were no longer being actively maintained by natural selection," they theorized.

This type of thing happened frequently in the history of the wild world, said study co-author Jonah Choiniere from the Division of Paleontology at the American Museum of Natural History.

"Vestigial structures, like legs in whales and snakes, may appear and disappear seemingly randomly in the course of evolution," he said.

"Linhenykus highlights the vestigiality of the outer fingers of advanced alvarezsauroids and underscores the complexity in evolution of these vestigial fingers."

The fossilized remains, which included vertebral bones, a forelimb, part of a pelvis and almost complete hind limbs, were dug up near the border between Mongolia and China in rocks of the Upper Cretaceous Wulansuhai Formation, which dates to 84-75 million years ago.

The site has yielded a treasure trove of vertebrate fossils.

The work wass published online Monday in Proceedings of the National Academy of Sciences (PNAS).

Image Courtesy Julius T. Csotonyi/PA


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