title: Rates of morphological evolution are heterogeneous in Early Cretaceous birds.
abstract: The Early Cretaceous is a critical interval in the early history of birds. Exceptional fossils indicate that important evolutionary novelties such as a pygostyle and a keeled sternum had already arisen in Early Cretaceous taxa, bridging much of the morphological gap between Archaeopteryx and crown birds. However, detailed features of basal bird evolution remain obscure because of both the small sample of fossil taxa previously considered and a lack of quantitative studies assessing rates of morphological evolution. Here we apply a recently available phylogenetic method and associated sensitivity tests to a large data matrix of morphological characters to quantify rates of morphological evolution in Early Cretaceous birds. Our results reveal that although rates were highly heterogeneous between different Early Cretaceous avian lineages, consistent patterns of significantly high or low rates were harder to pinpoint. Nevertheless, evidence for accelerated evolutionary rates is strongest at the point when Ornithuromorpha (the clade comprises all extant birds and descendants from their most recent common ancestors) split from Enantiornithes (a diverse clade that went extinct at the end-Cretaceous), consistent with the hypothesis that this key split opened up new niches and ultimately led to greater diversity for these two dominant clades of Mesozoic birds.
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, 142 Xizhimenwai Street, Beijing 100044, People's Republic of China wangmin@ivpp.ac.cn.
authors.forename: Min
authors.identifier: 0000-0001-8506-1213
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Biological Sciences, Faculty of Science, Macquarie University, Sydney, New South Wales 2109, Australia graemetlloyd@gmail.com.
authors.forename: Graeme T
authors.initials: GT
authors.lastname: Lloyd
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology*; D005580:Fossils / Q000033:anatomy & histology*; D010802:Phylogeny
keywords: Aves; Cretaceous; evolutionary rates; phylogeny; tempo