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Understanding Individual and Taphonomic Variation Using 3D Geometric Morphometrics University of Pennsylvania ScholarlyCommons VP3D Publications Vertebrate Paleontology 3D Database 8-9-2013 Lujiatun Psittacosaurids: Understanding Individual and Taphonomic Variation Using 3D Geometric Morphometrics Brandon P. Hedrick University of Pennsylvania, [email protected] Peter Dodson University of Pennsylvania, [email protected] This paper is posted at ScholarlyCommons. https://repository.upenn.edu/vp3d_pubs/1 For more information, please contact [email protected]. Lujiatun Psittacosaurids: Understanding Individual and Taphonomic Variation Using 3D Geometric Morphometrics Abstract Psittacosaurus is one of the most abundant and speciose genera in the Dinosauria, with fifteen named species. The genus is geographically and temporally widespread with large sample sizes of several of the nominal species allowing detailed analysis of intra- and interspecific ariation.v We present a reanalysis of three separate, coeval species within the Psittacosauridae; P. lujiatunensis, P. major, and Hongshanosaurus houi from the Lujiatun beds of the Yixian Formation, northeastern China, using three- dimensional geometric morphometrics on a sample set of thirty skulls in combination with a reevaluation of the proposed character states for each species. Using these complementary methods, we show that individual and taphonomic variation are the joint causes of a large range of variation among the skulls when they are plotted in a morphospace. Our results demonstrate that there is only one species of Psittacosaurus within the Lujiatun beds and that the three nominal species represent different taphomorphotypes of P. lujiatunensis. The wide range of geometric morphometric variation in a single species of Psittacosaurus implies that the range of variation found in other dinosaurian groups may also be related to taphonomic distortion rather than interspecific ariation.v As the morphospace is driven primarily by variation resulting from taphonomic distortion, this study demonstrates that the geometric morphometric approach can only be used with great caution to delineate interspecific ariationv in Psittacosaurus and likely other dinosaur groups without a complementary evaluation of character states. This study presents the first application of 3D geometric morphometrics ot the dinosaurian morphospace and the first attempt ot quantify taphonomic variation in dinosaur skulls. Disciplines Paleobiology | Paleontology This journal article is available at ScholarlyCommons: https://repository.upenn.edu/vp3d_pubs/1 Lujiatun Psittacosaurids: Understanding Individual and Taphonomic Variation Using 3D Geometric Morphometrics Brandon P. Hedrick1*, Peter Dodson1,2 1 Department of Earth and Environmental Science, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America, 2 School of Veterinary Medicine, Department of Animal Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America Abstract Psittacosaurus is one of the most abundant and speciose genera in the Dinosauria, with fifteen named species. The genus is geographically and temporally widespread with large sample sizes of several of the nominal species allowing detailed analysis of intra- and interspecific variation. We present a reanalysis of three separate, coeval species within the Psittacosauridae; P. lujiatunensis, P. major, and Hongshanosaurus houi from the Lujiatun beds of the Yixian Formation, northeastern China, using three-dimensional geometric morphometrics on a sample set of thirty skulls in combination with a reevaluation of the proposed character states for each species. Using these complementary methods, we show that individual and taphonomic variation are the joint causes of a large range of variation among the skulls when they are plotted in a morphospace. Our results demonstrate that there is only one species of Psittacosaurus within the Lujiatun beds and that the three nominal species represent different taphomorphotypes of P. lujiatunensis. The wide range of geometric morphometric variation in a single species of Psittacosaurus implies that the range of variation found in other dinosaurian groups may also be related to taphonomic distortion rather than interspecific variation. As the morphospace is driven primarily by variation resulting from taphonomic distortion, this study demonstrates that the geometric morphometric approach can only be used with great caution to delineate interspecific variation in Psittacosaurus and likely other dinosaur groups without a complementary evaluation of character states. This study presents the first application of 3D geometric morphometrics to the dinosaurian morphospace and the first attempt to quantify taphonomic variation in dinosaur skulls. Citation: Hedrick BP, Dodson P (2013) Lujiatun Psittacosaurids: Understanding Individual and Taphonomic Variation Using 3D Geometric Morphometrics. PLoS ONE 8(8): e69265. doi:10.1371/journal.pone.0069265 Editor: Alistair Robert Evans, Monash University, Australia Received March 19, 2013; Accepted June 7, 2013; Published August 9, 2013 Copyright: ß 2013 Hedrick, Dodson. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This project was funded by grant support from NSF EAR 1024671, University of Pennsylvania Research Foundation, and the EES Paleobiology Summer Research Stipend. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: Peter Dodson is a PLOS ONE editorial board member. This does not alter the authors’ adherence to all of the PLOS ONE policies on sharing data and materials. * E-mail: [email protected] Introduction with the fossiliferous layers shows that the Lujiatun specimens are Barremian (123.261.0 Ma) in age [7] rather than Hauterivian Psittacosaurus was first described from a well-preserved skeleton (12860.2 Ma) as was earlier reported [8] and thus that the found during the Third Asiatic Expedition to Mongolia in 1922 Psittacosauridae occupies a shorter temporal duration than [1,2]. Since then, 15 species and a genus separate from previously supposed. The Lujiatun beds are famous for producing Psittacosaurus have been placed in the Psittacosauridae [3]. The beautiful specimens of feathered dinosaurs and early birds (see [9] most recent review of the group accepts one genus (Psittacosaurus) for a review), but have also produced two named species of and nine species as valid categorizing the remaining species as Psittacosaurus (P. lujiatunensis and P. major) [6,10] and a separate either junior synonyms or as nomina dubia [3]. Psittacosaurus is one genus within the Psittacosauridae, Hongshanosaurus houi [11]. of the most common dinosaurs currently known and is found Sereno [3] found Hongshanosaurus to be a taphonomically distorted throughout Asia (Russia, China, Mongolia, and possibly Thai- Psittacosaurus skull and a junior synonym of Psittacosaurus with P. land). Further, it has been inferred to have a long temporal houi, a nomen dubium. He found both P. major and P. lujiatunensis to duration from the Hauterivian to the Albian stages of the Early be valid, though he points out many similarities between the two Cretaceous encompassing 20 Ma [4]. This wide geographical taxa and suggested more work needs to be done to clarify their distribution in combination with a long temporal duration coupled relationships. Erickson et al. [12] proposed that P. major is with small body size makes the Psittacosauridae one of the most synonymous with P. lujiatunensis reasoning that two similar species likely groups in the Dinosauria to have multiple congeneric species without trophic specializations would not inhabit the same [5]. environment. However, numerous extant environments in which The purported Hauterivian dates are based on ashes from the similar species and subspecies live within the same habitats (Buteo, Lujiatun beds of the Yixian Formation in Liaoning, northeastern Falco, Branta, Anolis, Odocoileus) do not support this assertion China, which is the oldest unit producing psittacosaur skeletons [13,14,15]. [4,6]. 40Ar/39Ar dating of ash from the Lujiatun beds interbedded PLOS ONE | www.plosone.org 1 August 2013 | Volume 8 | Issue 8 | e69265 Lujiatun Psittacosaurids Geometric morphometrics is an important method for demon- temporal and geographic variation. Thirty psittacosaurid skulls strating shape variation within a species given a large enough were digitized including the adult paratype of Hongshanosaurus houi specimen sample size [16]. In one of the first studies examining (IVPP [Institute of Vertebrate Paleontology and Paleoanthropol- species validity in dinosaurs using traditional morphometrics, ogy, Beijing, China] V12617), and the holotypes P. lujiatunensis Dodson [17] examined the skull of Corythosaurus, which resulted in (ZMNH [Zhejiang Museum of Natural History, Hangzhou, reducing the number of Corythosaurus species from six to one. The China] M8137), and P. major (LHPV1 [Long Hao Institute for species grouped into two separate groups, which were interpreted Stratigraphic Paleontology, Hohhot, Nei Mongol Autonomous as two sexual dimorphs of one species [17]. Recent work using Region, China]). Unfortunately the holotype of Hongshanosaurus high-resolution stratigraphy of the Dinosaur Park Formation
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