The haplocheirus sollers, here a reconstruction, lived 160 million years ago. He is one of the bird-like Alvarezsauriden that have been dated 60 million years younger. The fossil found now proves that these dinosaurs have evolved independently of birds. Picture: Portia Sloan
Read More 89 million years ago, the bird-like dinosaur group of the Alvarezsaurides roamed the Cretaceous. But these bipeds with a sharp claw on their forearms were not flightless birds: an Alvarezsaurid fossil of the "haplocheirus soller" excavated by US researchers in the Gobi Desert is fifteen million years older than the primitive bird Archeopteryx. However, both lines undoubtedly go back to a common branch of evolution: the group of bipedal and mostly carnivorous theropods whose reign began over the earth 228 million years ago. The mass extinction at the end of the Cretaceous period 65 million years ago survived only the birds. Alvarezsauridae were first dug up in 1920, but it was not until 1990 that scientists ventured a description because the fossils seemed too puzzling to them. The skeletons showed with small sternum, some feathery structures and the overgrown carpal and metacarpal bone high matches with the bone structure of birds. The bipeds detected in Asia, Europe and America from 89 to 65 million years ago were classified as flightless offspring of the birds. Haplocheirus now increases the age of this strain by 63 million years and demands its evolutionary autonomy.

The nearly complete skeleton of the haplocheirus was uncovered in ancient river deposits in the Junggar Basin of northwestern China's Xinijiang region in a joint digging campaign by Chinese and US scientists. At two meters in length, it is the largest Alvarezsauride ever found. But not only his body measurements differentiate him from his descendants: These have on very short forelegs a sharp claw next to two completely receded toe remnants, in the ancestor, there are three toes, of which the middle, however, is already significantly extended. The strong arm stubs with the sharp sickle claw were used in the view of the scientists to break up hard termite buildings. The Latin "sollers" means "sent": Haplocheirus could reach with his fingers.

"Haplocheirus is a transitional fossil. It shows how, at an early stage of evolution, the bizarre claw of the later Alvarezsaurids evolved from long-living predatory dinosaurs, "explains Jonah Choiniere of George Washington University in Washington. "And it confirms our prediction that this species already existed in the late Jurassic period." The paleontologists team discovered more extraordinary finds in its excavations: Among other things, the oldest dinosaur with horn-like humps called Yinlong downsi and the oldest were excavated Tyrannosaurus, the three meter long predator Guanlong wucaii.

Jonah Choiniere (George Washington University, Washington) et al .: Science, doi: 10.1038 / nature08740 ddp / Rochus Rademacher advertisement


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