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 Early relative of T-rex found in China  infographic
Graphic shows details of theropod Linhenykus described in the Proceedings of the National Academy of Sciences.
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SCIENCE

Early relative of T-rex found in China

By Duncan Mil

January 24, 2011 - Researchers have discovered a cousin of today’s birds which was also a tiny ancestor of Tyrannosaurus rex. Named Linhenykus monodactylus, it lived 84 to 75 million years ago during the Upper Cretaceous period.

Researchers probing ancient rock formations in Inner Mongolia have discovered a previously undescribed species of dinosaur, the Proceedings of the National Academy of Sciences reported Monday.

The animal is a member of the Alvarezsauridae, a family of small, long-legged running theropods related to the great predators including Tyrannosaurus rex and Velociraptor.

The fossilized remains were found by Xing Xu of the Chinese Academy of Sciences and Jonah Choiniere of the American Museum of Natural History. They were in Upper Cretaceous sandstone layers, 85 to 75 million years old, at Bayan Mandahu, north of the city of Linhe, near China’s northern border with Mongolia.

Named Linhenykus monodactylus, the tiny alvarezsaur was about the size of a large parrot and weighed less than half a kilogram.

Until recently alvarezsaurs were believed to be ancient, flightless birds, but now they are thought to be dinosaurs that share convergences‚ with birds.

Alvarezsaurs show the convergent evolution of some features that we previously thought were only present in birds, explained Dr. Choiniere. This means that alvarezsaurs independently evolved things like a keeled sternum, muscle attachments in the knee, and a fused wrist that we previously thought were unique to birds.

Alvarezsaurs have only recently been described in scientific literature. The first birdlike‚ dinosaur was discovered in the 1920s in Mongolia by the Indiana Jones-style adventurer Roy Chapman Andrews. It was to collect dust, unprepared and unexamined, at the American Museum of Natural History in New York for 70 years.

In the 1990s, several more specimens were unearthed in Late Cretaceous rocks in China’s Gobi Desert, Patagonia in South America, Montana in the United States and Alberta, Canada.

While most theropods have three-fingered hands, the hands of alvarezsaurs are dominated by a powerful claw surrounded by two scrawny fingers that probably had little functional importance. However, Linhenykus has just one large claw on each of its hands and is the only known dinosaur with one finger.

What Linhenykus tells us is that this reduction [in fingers] wasn’t just the progressive loss of these digits during the course of evolution, rather these reduced fingers seem to come and go during the evolution of alvarezsaurs, said Choiniere. In this respect, the side fingers of alvarezsaurs are like the legs we sometimes find in snakes and whales -- no longer necessary, but indicative of a shared evolutionary history.

Sources
PUBLISHED: 24/01/2011; STORY: Duncan Mil; PICTURES: National Academy Sciences
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