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Abstract
ABSTRACT—The Early Triassic ichthyopterygian Chaohusaurus chaoxianensis was previously known from juvenile specimens only. It was considered to represent immature forms of C. geishanensis, which was based on a single adult specimen, because allometric regression lines of the forelimb skeletons suggested that the two name groups fitted along a single growth trajectory. The sample size for the analysis, however, was small (n = 5). We collected new specimens of Chaohusaurus from Majiashan, Chaohu City, Anhui Province, China, through field excavations that started in 2010. New specimens included an immature individual whose forelimb resembled that of mature C. geishanensis, as well as a large adult individual whose forelimb retained the characteristics of immature C. chaoxianensis. Therefore, C. chaoxianensis is not the juvenile of C. geishanensis. With the addition of the new specimens, two growth trajectories are now clearly detected on allometric regression plots (n = 15). The two species are unambiguously distinguished from each other based on a suite of discrete characters that are diagnostic to each species, as well as statistical analyses of forelimb measurements. It is unlikely that the two forms represent the genders of a single species given that C. geishanensis is vastly outnumbered by C. chaoxianensis and completely lacking in major fossiliferous rock layers. Therefore, C. chaoxianensis should be resurrected as a valid species.
ACKNOWLEDGMENTS
We are grateful to Y. Sun, Z. Sun, and C. Ji for their help with the present project. We thank W. Chen, Y. Li, L. Ma, H. Lin, J. Sun, P. Yang, and X. Zou for their dedication to our field work program that enabled this study. We also thank T. Hu and T. Sato for fossil preparation. Field work was supported by National Geographic Society Committee for Research and Exploration (no. 8669-09) to R.M., Projects 40920124002 and 41372016 from the National Natural Science Foundation of China to D.J., Project 123102 from State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) to D.J., Project 20120001110072 from the Research Fund for the Doctoral Program of Higher Education to D.J., and a Project from the Department of Land and Resource of Anhui Province to G.C.
Handling editor: Robin O'Keefe.