Chapter 10 A Triassic Mystery Solved: Fertile Pekinopteris From the Triassic of North Carolina, United States Brian Axsmith 1 , Judith Skog 2 and Christian Pott 3, 4 1 University of South Alabama, Mobile, AL, United States; 2 George Mason University, Fairfax, VA, United States; 3 Swedish Museum of Natural History, Stockholm, Sweden; 4 LWL-Museum für Naturkunde, Münster, Germany 1. INTRODUCTION Pekinopteris auriculata was first described as a new genus and species of vascular plant fossil based on isolated pinnate fronds from the now classic Boren Clay Products pit locality in the Upper Triassic of the Deep River Basin in North Carolina, United States (Hope and Patterson, 1970). The Boren locality exposes sediments of the middle Pekin Formation, and has produced a diverse paleoflora (Gensel, 1986). Pekinopteris is one of the most abundant plant fossils from this site. Hope and Patterson (1970) noted that a plant possibly representing this species was confusingly described, and perhaps intermixed, with Cladophlebis reticulata specimens from the New Oxford Formation in the Upper Triassic Gettysburg Basin of York County, Pennsylvania by Fontaine and Wanner (1900); however, the precise identity and provenance of this material are unclear. The first author has collected extensively in the New Oxford Formation and has found no evidence of Pekinopteris. If it did occur outside of the Deep River Basin area, it was rare. One of the most intriguing aspects of Pekinopteris is that it has been known only from sterile specimens since its initial description. Therefore, the true affinities of this plant have been a persistent enigma to researchers concerned with the Triassic paleobotany of eastern North America (Hope and Patterson, 1970; Delevoryas and Hope, 1978; Gensel, 1986). Despite the lack of fertile material, Hope and Patterson (1970) suggested assignment of Pekinopteris to the ferns based on the apparently delicate texture of the pinnae along with the presence of occasional circinnate fronds, but they noted that pteridosperm or cycadalean affinities could not be entirely ruled out. Based on the later discovery of abundant new specimens from the Boren locality, Delevoryas and Hope (1978) described its growth habit based on fronds attached to creeping rhizomes with adventitious roots, and provided additional details of the morphology. A reconstruction of the plant was presented to show the overall growth form. Although the combination of thin, pinnate fronds with circinnate vernation and a creeping rhizomatous growth pattern supported assignment to the ferns, the absence of fertile material was still problematical, especially considering that other ferns from the Boren locality are known from abundant fertile specimens despite being less common (Axsmith et al., 2001). We have recently reexamined the Boren locality material now housed at the University of Kansas, Lawrence, Kansas, and have discovered the fertile portion of the fronds of Pekinopteris auriculata. These fertile parts are rare and mostly detached but are found in association with the abundant sterile fronds. This may be the reason they went unrecognized as parts of Pekinopteris for so long. However, three specimens show unambiguous attachment to sterile frond material. These newly recognized specimens confirm assignment to the ferns and indicate a relationship to the Schizaeales based on the structure of the sporangia. This material is described herein, and the possible relationships are discussed in greater detail. An updated reconstruction is also presented. Transformative Paleobotany. https://doi.org/10.1016/B978-0-12-813012-4.00010-3 Copyright © 2018 Elsevier Inc. All rights reserved. 179