Mar. 24, 1998 March 19, 1998--A team of researchers from the American Museum of Natural History and George Washington University announced today in the journal Nature the discovery of the first known skulls of a bizarre group of ancient animals called the Alvarezsauridae. This group (which includes the creature called Mononykus), is of special interest because it provides further evidence in support of the theory that birds evolved from dinosaurs and reveals an advanced stage in this transition. Numerous physical characteristics in the fossil skulls show that these strange creatures were actually early birds, challenging the traditional view that all primitive birds looked similar to their modern-day cousins.
The new fossils, which date from the late Cretaceous Period and are approximately 70 million years old, were found in the Gobi Desert of Mongolia. They were discovered during one of a series of joint American Museum of Natural History/Mongolian Academy of Sciences expeditions to search for dinosaurs and other fossils.
The research team named their find Shuvuuia deserti, from the Mongolian word shuvuu, meaning "bird," and the Latin for desert, in reference to the ancient climate in which the animals lived. Shuvuuia deserti, which was about the size of a turkey, walked on two legs, had a long tail and neck, and quite unlike most primitive birds, had stubby forearms that ended in a single, blunt claw. How the animals used these strange appendages is a mystery, but they were clearly unable to fly.
While creatures similar to Shuvuuia deserti, including the early bird Mononykus, have been found in Mongolia, Argentina, and North America, none of the specimens was found with a skull. Fossil skulls are extremely important because they contain key physical characteristics that enable researchers to trace the evolutionary history of different lifeforms.
The Shuvuuia deserti skulls reveal an important physical characteristic that is found only in birds: the animal was capable of "prokinesis," the movement of the snout up and down independently of the rest of the skull. This allowed the animal to open its mouth quite wide in order to eat large food items. The diet of Shuvuuia deserti is not known, but may have included insects, as well as lizards and even small mammals. Prokinesis is considered a very advanced characteristic of birds - to find evidence of this characteristic in such a primitive bird is surprising and indicates that this ability actually arose early in bird evolution.
A detailed analysis of its anatomical features shows that Shuvuuia deserti and all other Alavarezsauridea are the most primitive known fossil birds with the exception of the famous Archaeopteryx, discovered in 1861. Ironically, while Archaeopteryx is more primitive, it fits the stereotypical conception of a bird much better than the more advanced Shuvuuia deserti. The new discovery illustrates the complexity of the evolution of birds and hints at the number of surprises yet to be uncovered in tracing the development of their lineage.
The authors of the Nature paper are: Luis M. Chiappe, Chapman Fellow and research associate in the Museum's Department of Ornithology; Mark A. Norell, chairman and curator in the Museum's Department of Vertebrate Paleontology; and James M. Clark, the Ronald Weintraub Assistant Professor of Biology, Department of Biological Sciences, George Washington University.
In addition to support from the American Museum of Natural History, the Gobi Expedition is supported by Mercedes-Benz, which is the principal sponsor of the Museum's 1997, 1998, and 1999 expeditions to Mongolia, providing both financial support and vehicles for use by the expedition team. The Gobi project is also supported by the National Science Foundation and the Jaffe Foundation.
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