title: A Comparative Morphological Study of the Jugal and Quadratojugal in Early Birds and Their Dinosaurian Relatives.
abstract: The zygoma (called jugal bar) in modern birds accounts for a large portion of the ventral margin of the cranium. As a delicate and rod-like element, the jugal bar is functionally integrated into the avian cranial kinesis, a unique property that allows the beak to be elevated or depressed with respect to the braincase and thus distinguishes birds from all other modern vertebrates. Developmental studies show that the jugal bar of modern birds is formed by the fusion of the jugal and quadratojugal that are ossified from separated centers. However, those two bones are unfused and exhibit complicated morphological variations in basal birds and their dinosaurian relatives. Moreover, the jugal and quadratojugal form rigid articulations with the postorbital and squamosal, respectively, consequently hindering the movement of the upper jaw in most non-avian dinosaurs and some basal birds. A comparative study of the jugal and quadratojugal morphology of basal birds and their close relatives such as dromaeosaurids and oviraptorids elucidates how modern birds has achieved its derived jugal bar morphology, and sheds light on the evolution of the postorbital configuration of birds. We propose that numerous morphological modifications of those two elements (morphology changes and reduced articulation with other elements) took place in early bird history, and some of them pertinent to the refinement of the cranial kinesis. Anat Rec, 300:62-75, 2017. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.|State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.
authors.forename: Min
authors.identifier: 0000-0001-8506-1213
authors.initials: M
authors.lastname: Wang
authors.affiliation: Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Han
authors.initials: H
authors.lastname: Hu
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology*; D025061:Dinosaurs / Q000033:anatomy & histology*; D005580:Fossils; D007568:Jaw / Q000033:anatomy & histology; D010802:Phylogeny; D012886:Skull / Q000033:anatomy & histology*; D015050:Zygoma / Q000033:anatomy & histology*
keywords: Cretaceous; bird; cranial kinesis; evolution; function; jugal bar; quadratojugal; zygoma