Journal of Paleontology, 91(3), 2017, p. 477–492 Copyright © 2017, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2016.156
New taxa and phyletic evolution of the Aeronian (Llandovery, Silurian) Petalocrinidae (Echinodermata, Crinoidea) in Guizhou, South China Block
Yingyan Mao,1,2 William I. Ausich,3 Yue Li,1* Jih-Pai Lin,4 and Caihua Lin5
1Key Laboratory of Economic Stratigraphy and Paleogeography, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China ⟨
yymao@nigpas.ac.cn⟩, ⟨
yueli@nigpas.ac.cn⟩ 2University of the Chinese Academy of Sciences, Beijing 100049, China 3School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA ⟨
ausich.1@osu.edu⟩ 4Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106, Taiwan ⟨
jplin@hotmail.com⟩ 5Library and Information Center, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China ⟨
chlin@nigpas.ac.cn⟩
Abstract.—Systematic paleontology of three new species of Petalocrinidae (Crinoidea) are documented from the carbonate-dominated units of the Shihniulan and equivalent Leijiatun formations (Llandovery, Silurian) of the Baisha, Fengxiang, and Shuibatang sections in Guizhou (China). New taxa are from the Upper Yangtze Epicontinental Sea of the South China Block. The new taxa include Petalocrinus stenopetalus new species, Spirocrinus circularis new species, and S. dextrosus new species. They have a narrow spatial and temporal (Aeronian) distribution. Evolutionary patterns of the four genera of Petalocrinidae are outlined based on the specialized characters of the fused arm plates. Phylogenetic analysis was used to assess morphological relationships within the Petalocrinidae. Petalocrinus inferior represents the plesiomorphic condition for the group and nests as a sister group of P. stenopetalus n. sp. and the Spirocrinus species used in this analysis and the clade exclusively comprised of Sinopetalocrinus. The phylogenetic analysis suggests that Petalocrinus, as currently defined, might be a paraphyletic genus.
Introduction
Research on Silurian Petalocrinidae began more than one century ago with studies in Iowa (Weller and Davidson, 1896) and Sweden (Bather, 1898). The key defining feature for the family is the presence of fused arm plates. The stratigraphic range of the Petalocrinidae is from Middle Ordovician (Li, 1993) to Early Devonian (Prokop, 1983 [1984]; Prokop and Petr, 2010). The oldest representative is Eopetalocrinus sinensis from the Dapingian (Middle Ordovician) Dawan Formation at the Songzi section, Hubei Province (Li, 1993). Petalocrinidae are not known from Darriwilian (late Middle Ordovician) through the Llandoverian (earliest Silurian) in China, but they became geographically widespread during the Llandovery. The youngest occurrence of the family is the Early Devonian Vadarocrinus from the Czech Republic (Prokop, 1983 [1984]). This family flourished during the Llandovery and Wenlock. Systematic study of early Silurian crinoids advanced con- siderably beginning in the 1980s with faunas reported from Iowa (Witzke and Strimple, 1981), Ohio (Ausich, 1984a, b, 1985, 1986a, b, c, d, 1987a, b; Ausich and Dravage, 1988; Boyarko and Ausich, 2009), Kentucky (Ausich et al., 2015), New York and Canada (e.g., Eckert, 1984, 1990; Eckert and Brett, 2001; Ausich and Copper, 2010), and Britain and Ireland (e.g., Donovan and Sevastopulo, 1989; Donovan, 1993;
* Corresponding author
Donovan and Harper, 2003; Donovan and Lewis, 2005; Fearnhead and Donovan, 2007a, b; Fearnhead and Harper, 2007; Donovan et al., 2008, 2009, 2010, 2012). All Silurian Petalocrinidae in China are from the Upper Yangtze Epiconti- nental Sea, South China Block. They have been identified as three genera, Petalocrinus, Spirocrinus, and Sinopetalocrinus (Mu, 1949 [1950]; Tien and Mu, 1955; Mu and Wu, 1974; Mu and Lin, 1987; Chen and Yao, 1993). Mao et al. (2015) summarized the geographic and temporal distribution of the Petalocrinidae, including 28 species belonging to five genera; and they hypothesized that the Upper Yangtze Epicontinental Sea was the center for the Ordovician origination and Silurian diversification of genera for this most unusual family. We found new material from three sections of the upper
Aeronian (Llandovery, Silurian) units, Shihniulan and Leijiatun formations (updated stratigraphic correlation following biozonations by Rong and Chen, 2000; Rong et al., 2003), during four years of recent field excursions (Fig. 1). In the present paper, one newspecies of Petalocrinus and two new species of Spirocrinus are described. Based on their morphology, phylogenetic relationships among the Petalocrinidae genera are proposed.
Geological setting
The Upper (today, western) Yangtze region of the South China Block was covered by an epicontinental sea with a southward extension of the Qianzhong Oldland during the
Silurian.After the
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