Journal of Paleontology, 91(5), 2017, p. 859–870 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.25


Reevaluation and taxonomic clarification of Gigantopteridium and Cathaysiopteris of western equatorial Pangea and their biogeographical significance


Rebecca A. Koll,1 William A. DiMichele,2 and Steven R. Manchester3


1Department of Biology, University of Florida, Gainesville, FL 32611, USA, Florida Museum of Natural History, 1659 Museum Road, PO Box 117800, Department of Paleobiology, NMNH, Smithsonian Institution, Washington, DC 20560, USA ⟨rebecca.koll@ufl.edu⟩ 2Department of Paleobiology, NMNH, Smithsonian Institution, Washington, DC 20560, USA ⟨dimichel@si.edu⟩ 3Department of Biology, University of Florida, Gainesville, FL 32611, USA, Florida Museum of Natural History, 1659 Museum Road, PO Box 117800 ⟨steven@flmnh.ufl.edu⟩


Abstract.—A reassessment of the taxonomic relationships of North American gigantopterids is presented in light of an examination of large populations of specimens housed in the US National Museum of Natural History. Variations in venation and subtle aspects of leaf shape facilitate refined understanding of the relationships and diversity of the North American gigantopterid species leading to an improved understanding of the taxonomic and biogeographic relationships of this group, which are found most abundantly in western equatorial Pangea and Cathaysia. Current literature suggests that there are eight North American genera, however, this study has revealed a morphological overlap of several previously defined genera, leading to the conclusion that Gigantopteridium encompasses the species previously treated as Cathaysiopteris yochelsonii as well as a new species, Gigantopteridium utebaturianum.The transfer of C. yochelsonii to Gigantopteridium yochelsonii suggests that Cathaysiopteris may represent a genus endemic to Cathaysia, limiting the biogeographical connection between the regions to Zeilleropteris, Gigantopteridium, Euparyphoselis,and Gigantonoclea.


Introduction


Gigantopterids, an enigmatic group of extinct plants known for their distinctive leaf architecture, including peculiar herringbone or polygonal mesh venation patterns, may hold significant biogeographic and paleoenvironmental information tied closely to their global and stratigraphic distribution. Occurrences of this plant group are most commonly recorded in western North America and eastern Asia, with scattered occurrences elsewhere in the former Pangean equatorial regions, including Turkey, Russia, Korea, and Malaysia (Kawasaki, 1934; Wagner, 1962; Kon’no and Asama, 1970; Burago, 1986). As proposed by Glasspool et al. (2004), gigantopterids are likely not mono- phyletic in nature and should be treated as an informal group when referring to the full suite of species; Glasspool et al. (2004) further limited gigantopterid sensu stricto to Gigantopteris and Gigantonoclea. Gigantopterids as discussed here include the taxa commonly recovered from western equatorial Pangea. Eight North American genera have been recognized; Gigantopteridium Koidzumi, Cathaysiopteris Koidzumi, Zeilleropteris Koidzumi, Gigantonoclea Koidzumi, Evolsonia Mamay, Delnortea Mamay, Euparyphoselis DiMichele, Looy, and Chaney, and Lonesomia Weber, each represented in North America by a single species (Mamay, 1960, 1967, 1986, 1988, 1989; Mamay et al., 1986, 1988; Weber, 1997; Glasspool et al., 2004; DiMichele et al., 2011). Additional species of some


genera also have been described from eastern Asia (Halle, 1927; Koidzumi, 1934, 1936; Gu and Zhi, 1974; Li and Yao, 1983; Shen, 1995; Yao and Liu, 2004; DiMichele et al., 2011). Rarely have the large-scale systematic or stratigraphic


patterns of the entire gigantopterid group been examined in detail, nor have the subtleties and range of morphological variation been considered fully in taxonomic investigations. Historically, a biogeographic connection between Cathaysia and western Pangea has been recognized at the generic level for gigantopterids. These areas were on opposite ends of the Pangean supercontinent and separated by the large Panthalassic Ocean. This study questions the presence of Cathaysiopteris in western Pangea as well as the validity of the generic assignment of Gigantopteridium huapingense (Feng) Shen, the only Cathaysian member of that genus (Liu and Yao, 2002; Booi et al., 2009). Current literature and the results of this study restrict the possible linkages of the two regions to Zeilleropteris, Gigantopteridium, Euparyphoselis,andGigantonoclea.Although species of these genera described from the two regions certainly share morphological similarities at the generic level, at this time, however, no species are known to occur in both paleo- geographic areas. This leaves open the possibility that the similarities of gross leaf architecture may be the result of convergence. The purpose of this study is to reassess North American Paleozoic Gigantopteridium and Cathaysiopteris and revise


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