Oct. 24-26, 2009, Yingjie Overseas Exchange Center, Peking University, Beijing, China中文版

The evolution of theropod hand

Xing Xu

Institute of Vertebrate Paleontology and Paleoanthropology, CAS, China

Abstract

The evolution of the theropod hand has been the focus of many recent studies in both paleontology and developmental biology, mainly because avian manual digital homologies are still heavily debated. The non-avian theropod hand has characteristics associated with grasping ability, and its primary function is inferred to have been predation; derived avians possess a highly modified hand, the primary function of which is flight; some transitional forms have a hand that is intermediate in morphology, and presumably also in function. The transformation from a five-fingered hand in basal theropods to a three-fingered hand in derived birds must have been a complex process from the perspectives of morphology, function, and development. The hands of basal, five-fingered theropods clearly show a lateral digital reduction pattern, which was probably a response to functional constraints, since the medial digits were needed for grasping. By contrast, there is some evidence for a complex digital reduction pattern in more derived theropods. There may have been a shift from predatory to non-predatory manual function at the base of the Averostra, followed by a shift back to predation at the base of the Tetanurae. It is inferred that interactions during this evolutionary period between a conservative developmental mechanism and immediate selection pressures finally resulted in a novel functional tridactyl hand, which first appeared in extinct tetanurans and was subsequently inherited by their living descendants. A major feature of the developmental part of this scenario is that homeotic changes might have been involved in theropod hand evolution. This possibility is suggested by a number of morphological features of the carpals, metacarpals, and phalanges of both extinct and living theropods, and by some developmental observations of the hands of the living ones. Such an evolutionary scenario best explains the available morphological and developmental data concerning the theropod hand, and can be tested in future by further morphological information from basal tetanurans and further developmental data from living theropods.

Xing Xu

Institute of Vertebrate Paleontology and Paleoanthropology, CAS, China

Biography

Xing Xu studies the dinosaurian taxonomy and systematics, focusing on the origin of birds and their flight, and the origin and early evolution of feathers.  One of Dr. Xu current research projects is to reconstruct a robust coelurosaurian phylogeny and analyze in depth the important modifications along the line to birds.  This project will yield an understanding of the evolutionary pattern of bird-like characters and allow him to identify the major stages of coelurosaurian locomotory evolution, and based on that reconstructing a scenario for the flight origin. Dr. Xu also is leading expeditions in Gobi deserts of western China, including the one in the Middle-Late Jurassic sediments, a period that is critical for the origin and early evolution of many vertebrate groups, including the major dinosaurian groups.  Dr. Xu has conducted fieldwork in the major dinosaur localities in China as well as Gobi desert in Mongolia.  He named more than 30 new dinosaur species, among them including four-winged Microraptor and the buck-toothed Incisivosaurus.  His works on the origin and early evolution of feathers and of bird flight are among the most significant contributions in these fields. He has published over 70 peer-reviewed papers, many of which are in journals of high profile such as Nature.  He is a professor at the Institute of Vertebrate Paleontology and Paleonanthropology, Chinese Academy of Sciences (IVPP).  Dr. Xu received a B.S. in paleontology from the Peking University in China in 1992 and a Ph.D. in paleontology from the IVPP in 2002