Journal of Paleontology, 92(1), 2018, p. 40–48 Copyright © 2017, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.77


A new radiodontan oral cone with a unique combination of anatomical features from the early Cambrian Guanshan Lagerstätte, eastern Yunnan, South China


Han Zeng,1,2,3 Fangchen Zhao,1* Zongjun Yin,1 and Maoyan Zhu1,4


1State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, No. 39 East Beijing Road, Nanjing 210008, China ⟨hzeng@nigpas.ac.cn⟩, ⟨fczhao@nigpas.ac.cn⟩, ⟨zjyin@nigpas.ac.cn⟩, ⟨myzhu@nigpas.ac.cn⟩ 2Department of Paleobiology, National Museum of Natural History, P.O. Box 37012, MRC-121, Washington, DC, 20013–7012, USA 3University of Chinese Academy of Sciences, No. 19 Yuquan Road, Beijing 100049, China 4College of Earth Sciences, University of Chinese Academy of Sciences, No. 19 Yuquan Road, Beijing 100049, China


Abstract.—The radiodontans, including anomalocaridids and their allies, are enigmatic stem-group euarthropods and are the most ancient apex giant predators known from the fossil record. Most studies on their feeding behaviors have emphasized their diverse and abundant raptorial frontal appendages, while the oral cone surrounding the mouth opening in these animals has attracted less attention. At present, three oral cone morphotypes are known, from Anomalocaris Whiteaves, 1892, Peytoia Walcott, 1911, and Hurdia Walcott, 1912, respectively. In this paper, we report on a novel form of radiodontan oral cone from the Guanshan Lagerstätte (Cambrian Series 2, Stage 4) in the Wulongqing Formation, eastern Yunnan, South China. This oral cone is unique in combining features seen in Peytoia/Hurdia and Anomalocaris. It possesses a Peytoia/Hurdia-type ‘tetraradial’ configuration comprising a 32-plate outer ring that consists of four perpendicularly arranged large plates and 28 small plates, in addition to furrowed folds and scale-like nodes on plate surfaces otherwise seen only in Anomalocaris. As an intermediate morphotype, the Guanshan oral cone improves our understanding of the occurrence and morphological disparity of radiodontan oral cones, illuminates future investigations on potentially variable radiodontan feeding mechanisms, and reveals possible evolutionary transformations of these peculiar feeding structures. The resolution of current radiodontan phylogeny would be potentially improved by new knowledge on other body parts apart from frontal appendages in future studies.


Introduction


The Radiodonta Collins, 1996, a clade comprising the anomalocaridids and their allies, is a lineage of soft-bodied stem- group euarthropods (Daley et al., 2013a; Ortega-Hernández, 2016) regarded as the oldest giant top predators in Paleozoic marine ecosystems (e.g., Whittington and Briggs, 1985; Chen et al., 1994). A series of ongoing discoveries from exceptionally preserved fossil deposits have revealed that radiodontans had a cosmopolitan distribution (e.g., Daley et al., 2013a) and a long fossil record from the Cambrian Stage 3 (Daley and Legg, 2015) to the EarlyOrdovician Tremadocian (VanRoy andBriggs, 2011; Van Roy et al., 2015), or even possibly to the Early Devonian Emsian (Kühl et al., 2009). As apex predators, the feeding beha- viors of radiodontans have become a major research topic (e.g., Briggs, 1979; Briggs and Mount, 1982; Whittington and Briggs, 1985; Nedin, 1999; Daley et al., 2013b; Vinther et al., 2014; Van Roy et al., 2015). However, the bulk of research on radiodontan feeding has focused on their frontal appendages, a pair of ante- riormost raptorial appendages known to have attained consider- able morphological disparity (Daley and Budd, 2010; Aria and Caron, 2015) and ecological adaptations to either macrophagous


* Corresponding author 40


predation (e.g.,Chen et al., 1994;Daley andEdgecombe, 2014) or filter feeding (Vinther et al., 2014; Van Roy et al., 2015). In addition to their frontal appendages, radiodontans pos-


sessed a second feeding organ, an oral cone consisting of a ring of radially arranged plates developed around the mouth, from which the group gets its name. The oral cone, however, has attracted much less research attention; while at one point it was thought to be used for biting and chewing prey (Whittington and Briggs, 1985), recent biomechanical modeling of the oral cone of Peytoia Walcott, 1911 (Hagadorn, 2009, 2010) and reconstruction of this structure in Anomalocaris Whiteaves, 1892 (Daley and Bergström, 2012) suggest that more likely it was involved in suction during the ingestion of food, rather than directly crushing prey. To date, only three radiodontan oral cone morphotypes have been recognized, primarily from fossil specimens from the Cambrian Stage 5 Burgess Shale, British Columbia, Canada (Daley and Bergström, 2012). These morphotypes include the ‘triradially’ symmetrical oral cone of Anomalocaris canadensis Whiteaves, 1892 (Daley and Bergström, 2012; Daley and Edgecombe, 2014) and the ‘tetraradially’ symmetrical oral cones of Peytoia nathorsti Walcott, 1911 (Whittington and Briggs, 1985; Daley and Bergström, 2012), Hurdia victoria Walcott, 1912, and H. triangulata Walcott, 1912. The oral cones of both Peytoia and Hurdia comprise 32 plates with


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