Australia: The Land Where Time Began

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Xiaotingia zhengi - a theropod dinosaur

Xing Xu et al. have published a paper in Nature in which they describe a new find in the Jehol Beds in China, Xiaotingia zhengi, an Archaeopteryx-like theropod, a small long-armed, 4-winged dinosaur that lived about 155 Ma. Following analysis of the new fossil it has been concluded by Xing et al. that Archaeopteryx is not at the base of the evolutionary line of birds, rather it is a non-avian dinosaur at the base of the Deinonychosauria, a group known for their switch-blade-like claws, and ancestral to forms such as Velociraptor. According to Xhing Xu et al., the status of Archaeopteryx has been weakened by the discovery of derived maniraptorans. They also suggest that many features, such as long, robust forelimbs, that were previously considered to be diagnostic of Avialae, are actually diagnostic of the Paraves, a more inclusive group that includes the avialans and the deinonychosaurs. When they added the new taxon into a comprehensive Phylogenetic analysis Archaeopteryx was moved into the Deinonychosauria. They claim their results challenge the placement of Archaeopteryx in a central position in the transition to birds. They await confirmation of their phylogenetic hypothesis by further investigation. If confirmation does indeed eventuate the avialan ancestral condition will need to be re-evaluated.

According to Lawrence Witmer of Ohio University, the basic understanding of birds as dinosaurs would be unchanged by shifting Archaeopteryx to the non-avian dinosaur line. He believes the evidence for the shift is good but needs confirmation to be more certain, and he suggests a re-evaluation of everything connected with the evolution of birds is in order. Other experts in the field, such as Luis Chiappe of the Dinosaur Institute, Natural History Museum of Los Angeles County, is still to be convinced by the analysis and the conclusions, believing the importance of the new fossil in the understanding of the origins of birds has been exaggerated, pointing out that the known fossil material of Archaeopteryx is by far the most anatomically informative in the immediate transition to birds, continuing to play an important role, wherever it is interpreted as a bird or immediately outside the bird line. He also points out that Archaeopteryx is known from 10 specimens that together provide a wealth of anatomical information, while Xiaotingia is so far known from a single partial specimen the age of which has not yet been positively determined.

Chiappe says the paper in Nature adds confirmation to the belief that birds fit in with the theropod dinosaurs "Birds are so tightly nested within the much bigger diversity of dinosaurs that the line between what is and what is not a bird has become completely blurred. We need to draw a line between birds and non-avian dinosaurs, and this line is increasingly more difficult to find."

Michael Benton of the University of Bristol has guessed that X. zhengi looked something like a rook in both size and general appearance - a head with as short snout and small beak, large eyes, wings that were well feathered, and a long tail that was covered with branching feathers. He suggested it may have ran and hopped about on the ground and possibly fly a bit clumsily.

Lawrence sees it as a bird-like dinosaur running around on its hind legs, with long feathers on its arms and legs, "Our first impression if we saw it today would be that it was a toothy bird, but then again, that would be true of almost all the small theropod dinosaurs of the Late Jurassic."

Sources &Further reading

  1. Xu, X., H. You, K. Du and F. Han (2011). "An Archaeopteryx-like theropod from China and the origin of Avialae." Nature 475(7357): 465-470.
  2. Anthony King, Cosmos Online, 28 July 2011


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  2. Xiaotingia zhengi
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Author: M. H. Monroe
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