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Earth and Environmental Science Transactions of the Royal Society of Edinburgh For Peer Review An unusual small -bodied crocodyliform from the Middle Jurassic of Scotland, UK, and potential evidence for an early diversification of advanced neosuchians Earth and Environmental Science Transactions of the Royal Society of Journal: Edinburgh Manuscript ID Draft Manuscript Type: Spontaneous Article Date Submitted by the Author: n/a Complete List of Authors: Yi, Hong-yu; Grant Institute, School of Geosciences; Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology Tennant, Jonathan; Imperial College London, Earth Science and Engineering Young, Mark; University of Edinburgh, School of GeoSciences Challands, Thomas; University of Edinburgh, School of GeoSciences Foffa, Davide; Grant Institute, School of Geosciences Hudson, John; University of Leicester, Department of Geology Ross, Dugald; Staffin Museum, Earth Sciences Brusatte, Stephen; Grant Institute, School of Geosciences; National Museums Scotland, Earth Sciences Keywords: Isle of Skye, Mesozoic, Duntulm Formation, Eusuchia origin Cambridge University Press Page 1 of 40 Earth and Environmental Science Transactions of the Royal Society of Edinburgh 1 An unusual small-bodied crocodyliform from the Middle Jurassic of Scotland, UK, and potential evidence for an early diversification of advanced neosuchians HONGYU YI 1, 2 , JONATHAN P. TENNANT 3*, MARK T. YOUNG 1, THOMAS J. CHALLANDS 1, DAVIDE FOFFA 1, JOHN D. HUDSON 4, DUGALD A. ROSS 5, and STEPHEN L. BRUSATTE 1, 6 For Peer Review 1 School of GeoSciences, Grant Institute, The King’s Buildings, University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK 2 Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, 100044, China 3 Department of Earth Science and Engineering, Imperial College London, London, SW6 2AZ, UK 4 Department of Geology, University of Leicester, University Road, Leicester LEI 7RH 5 Staffin Museum, 6 Ellishadder, Staffin, Isle of Skye IV51 9JE, UK 6 National Museums Scotland, Chambers Street, Edinburgh EH1 1JF, UK #These authors listed alphabetically * Corresponding author: [email protected] RUNNING HEAD : Middle Jurassic crocodyliform from Scotland, UK Cambridge University Press Earth and Environmental Science Transactions of the Royal Society of Edinburgh Page 2 of 40 2 ABSTRACT The Middle Jurassic is a poorly sampled time interval for non-marine neosuchian crocodyliforms, which obscures our understanding of the origin and early evolution of major clades. Here we report a lower jaw from the Middle Jurassic (Bathonian) Duntulm Formation of the Isle of Skye, Scotland, UK, which consists of an isolated and incomplete left dentary and part of the splenial. Morphologically, the Skye specimen closely resembles CretaceousFor hylaeochampsids,Peer Review including Pachycheilosuchus and Pietraroiasuchus , in having a proportionally short mandibular symphysis, shallow dentary alveoli, a strongly laterally compressed dentary, and inferred weakly heterodont dentition. It differs from other crocodyliforms in that the Meckelian canal is dorsoventrally expanded posterior to the mandibular symphysis and drastically constricted at the 6 th alveolus. We tentatively refer the new specimen to cf. Hylaeochampsidae sp. which, together with the presence of Theriosuchus sp. from the Valtos Formation and indeterminate neosuchians from the Kilmaluag Formation, indicates the presence of a previously unrecognized highly diverse crocodyliform fauna in the Middle Jurassic of Skye, and Europe more generally. This new specimen indicates that small-bodied neosuchians were present, and ecologically and taxonomically diverse, in nearshore environments in the Middle Jurassic of the UK. Key words: Isle of Skye, Mesozoic, Duntulm Formation, Eusuchia origin Cambridge University Press Page 3 of 40 Earth and Environmental Science Transactions of the Royal Society of Edinburgh 3 Modern crocodiles and alligators are the only living members of Crocodyliforms, a group of archosaurs whose evolutionary history spans about 200 million years (Whetstone and Whybrow, 1983; Benton and Clark, 1988; Bronzati et al., 2015; Mannion et al., 2015). The Middle Jurassic was a key period in their evolution, with thalattosuchians rapidly diversifying in the marine realm (e.g., Gasparini and Chong, 1977; Young et al., 2010, 2011; Wilberg, 2015). Much less is known about the non-marine crocodyliforms from this time, however.For Apparently Peer terrestrial and Reviewfreshwater species were stuck in a low point of their diversity, although this could be an artefact of the notoriously poor Middle Jurassic fossil record. Sparse sampling during this interval complicates our understanding of non-marine crocodyliform diversification patterns (Bronzati et al., 2015; Mannion et al., 2015; Tennant et al., 2016), meaning that new Middle Jurassic fossils are critical. Indeed, non-marine crocodyliform faunas during the Middle Jurassic remain poorly understood compared with other geological intervals. During the Late Jurassic, most crocodyliforms in Europe were goniopholidids and atoposaurids (Andrade et al., 2011; Young et al., 2016; Tennant et al., in press), and at the same time small-bodied sphenosuchian and protosuchian-grade taxa were widely distributed in other parts of the world (Gao, 2001; Clark et al., 2004; Göhlich et al., 2005; Pol et al., 2013). By the Early Cretaceous, the European faunas comprised a more diverse assemblage of neosuchians, including goniopholidids, pholidosaurids, bernissartiids, putative atoposaurids, and hylaeochampsids (e.g., Salisbury and Naish, 2011; Sweetman et al., 2015). Depending on the systematic position of these Cretaceous neosuchian clades, ghost lineages imply that some of these major lineages may have gotten their start during the dark period of the Cambridge University Press Earth and Environmental Science Transactions of the Royal Society of Edinburgh Page 4 of 40 4 Middle Jurassic (e.g., Bernissartiidae, Hylaeochampsidae, Paralligatoridae, and Pholidosauridae: Bronzati et al., 2015; Turner, 2015; Tennant et al., 2016). The problem, however, is that there are few places where Jurassic (and in particular Middle Jurassic) crocodyliforms can be found. Non-marine fossil-bearing beds of the Jurassic are sparsely distributed in China (Gao, 2001; Maisch et al., 2003; Fu et al., 2005), Kyrgyzstan (Averianov, 2000), parts of Europe (Evans and Milner, 1994; Kriwet et al., 1997; Knoll Foret al., 2013; Peer Knoll and López-A Reviewntoñanzas, 2014; Young et al., 2016), and Russia (Kuzmin et al., 2013), and these have yielded some crocodyliform fossils. Furthermore, there are undescribed crocodyliform teeth of this age from Thailand (Tong et al., 2002) and possible remains from Madagascar (Dal Sasso and Pasini, 2003; Flynn et al., 2006), but these are fragmentary. The vast majority of Middle Jurassic crocodyliform fossils are isolated specimens from microvertebrate localities—limited evidence that makes it difficult to assign these fossils to higher-level clades, which in turn hinders our understanding of the origin and early evolution of these groups that would later go on to great diversity and success in the Cretaceous and beyond. Here we report a new crocodyliform lower jaw from the Middle Jurassic of the Isle of Skye, Scotland, UK (Fig. 1). This study is part of an ongoing investigation of the world-class Middle Jurassic vertebrate fossil record of Skye, led by the PalAlba Group (Brusatte et al., 2015a, 2015b; Brusatte and Clark, 2015; Young et al., 2016). Previously identified crocodyliforms from Skye include indeterminate remains (Evans et al., 2006; Wills et al., 2014) and a partial skeleton (Evans and Waldman, 1996) from Cladach a’Ghlinne (Fig. 1B) and a partial lower jaw assigned to Theriosuchus sp. (Young et al., 2016) from Valtos (Fig. 1B). The new specimen represents a hitherto unknown small- Cambridge University Press Page 5 of 40 Earth and Environmental Science Transactions of the Royal Society of Edinburgh 5 bodied taxon from the Middle Jurassic Skye tetrapod assemblage, and has implications for the diversity and ecology of non-marine crocodyliforms of the poorly-sampled Middle Jurassic. Institutional abbreviations AMNH, American Museum of Natural History, New York, USA. IPFUB, InstitutFor für Paläontologie Peer der FreieReview Universität Berlin, Berlin, Germany. NHMUK, Natural History Museum, London, UK. NMS, National Museums Scotland, Edinburgh, UK. PC-1, provisional specimen number for Pietraroiasuchus ormezzanoi Buscalioni et al., 2011 at Museo Regionale di Scienze Naturali di Torino, Italy. SMU, Shuler Museum of Paleontology, Southern Methodist University, Dallas, USA. 1. Systematic Palaeontology CROCODYLIFORMES BENTON & CLARK, 1988 MESOEUCROCODYLIA WHETSTONE & WHYBROW, 1983 NEOSUCHIA BENTON & CLARK, 1988 cf. Hylaeochampsidae sp. Specimen NMS G.2016.21.1: an isolated and incomplete, three-dimensionally preserved left lower jaw, including much of the dentary and part of the splenial. It is broken posterior to where the Meckelian canal enters the dentary. Cambridge University Press Earth and Environmental Science Transactions of the Royal Society of Edinburgh Page 6 of 40 6 Differential diagnosis A small-bodied crocodyliform, differing from other members of the group in the following features: Meckelian canal dorsoventrally expanded posterior to the mandibular symphysis and constricted at the 6 th alveolus; mandibular symphysis mediolaterally thin

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