title: Homologies and homeotic transformation of the theropod 'semilunate' carpal.
abstract: The homology of the 'semilunate' carpal, an important structure linking non-avian and avian dinosaurs, has been controversial. Here we describe the morphology of some theropod wrists, demonstrating that the 'semilunate' carpal is not formed by the same carpal elements in all theropods possessing this feature and that the involvement of the lateralmost distal carpal in forming the 'semilunate' carpal of birds is an inheritance from their non-avian theropod ancestors. Optimization of relevant morphological features indicates that these features evolved in an incremental way and the 'semilunate' structure underwent a lateral shift in position during theropod evolution, possibly as a result of selection for foldable wings in birds and their close theropod relatives. We propose that homeotic transformation was involved in the evolution of the 'semilunate' carpal. In combination with developmental data on avian wing digits, this suggests that homeosis played a significant role in theropod hand evolution in general.
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology &Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044.
authors.forename: Xing
authors.initials: X
authors.lastname: Xu
authors.affiliation: Faculty of Earth Sciences, China University of Geosciences, No. 388 Lumo Road, Wuhan 430074, People's Republic of China.
authors.forename: Fenglu
authors.initials: F
authors.lastname: Han
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology &Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhao
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology*; D002348:Carpal Bones / Q000033:anatomy & histology* / Q000502:physiology; D025061:Dinosaurs / Q000033:anatomy & histology*; D005580:Fossils; D014921:Wings, Animal / Q000033:anatomy & histology* / Q000502:physiology