title: The oldest North American pachycephalosaurid and the hidden diversity of small-bodied ornithischian dinosaurs.
abstract: Taphonomic biases dictate how organisms are represented in the fossil record, but their effect on studies of vertebrate diversity dynamics is poorly studied. In contrast to the high diversity and abundance of small-bodied animals in extant ecosystems, small-bodied dinosaurs are less common than their large-bodied counterparts, but it is unclear whether this reflects unique properties of dinosaurian ecosystems or relates to taphonomic biases. A new, fully domed pachycephalosaurid dinosaur, Acrotholus audeti, from the Santonian of Alberta predates incompletely domed taxa, and provides important new information on pachycephalosaur evolution and the completeness of the ornithischian fossil record. Here we provide the first empirical evidence that the diversity of small-bodied ornithischian dinosaurs is strongly underestimated based on ghost lineages and the high proportion of robust and diagnostic frontoparietal domes compared with other pachycephalosaur fossils. This suggests preservational biases have a confounding role in attempts to decipher vertebrate palaeoecology and diversity dynamics through the Mesozoic.
authors: Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto, Ontario, Canada M5S 2C6. d.evans@utoronto.ca
authors: David C
authors: DC
authors: Evans
authors: Ryan K
authors: RK
authors: Schott
authors: Derek W
authors: DW
authors: Larson
authors: Caleb M
authors: CM
authors: Brown
authors: Michael J
authors: MJ
authors: Ryan
mesh_terms: D000818:Animals; D044822:Biodiversity; D001717:Birds / Q000033:anatomy & histology*; D049628:Body Size; D025061:Dinosaurs / Q000033:anatomy & histology*; D005580:Fossils; D021621:Imaging, Three-Dimensional; D009656:North America; D010163:Paleontology; D010802:Phylogeny; D025341:Principal Component Analysis; D013997:Time Factors; D014057:Tomography, X-Ray Computed
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