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A New Phylogenetic Hypothesis of Tanystropheidae Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2021 A new phylogenetic hypothesis of Tanystropheidae (Diapsida, Archosauromorpha) and other “protorosaurs”, and its implications for the early evolution of stem archosaurs Spiekman, Stephan N F ; Fraser, Nicholas C ; Scheyer, Torsten M Abstract: The historical clade “Protorosauria” represents an important group of archosauromorph rep- tiles that had a wide geographic distribution between the Late Permian and Late Triassic. “Pro- torosaurs” are characterized by their long necks, which are epitomized in the genus Tanystropheus and in Dinocephalosaurus orientalis. Recent phylogenetic analyses have indicated that “Protorosauria” is a polyphyletic clade, but the exact relationships of the various “protorosaur” taxa within the archosauro- morph lineage is currently uncertain. Several taxa, although represented by relatively complete material, have previously not been assessed phylogenetically. We present a new phylogenetic hypothesis that comprises a wide range of archosauromorphs, including the most exhaustive sample of “protorosaurs” to date and several “protorosaur” taxa from the eastern Tethys margin that have not been included in any previous analysis. The polyphyly of “Protorosauria” is confirmed and therefore we suggest the usage of this term should be abandoned. Tanystropheidae is recovered as a monophyletic group and the Chinese taxa Dinocephalosaurus orientalis and Pectodens zhenyuensis form a new archosauromorph clade, Dinocephalosauridae, which is closely related to Tanystropheidae. The well-known crocopod and former “protorosaur” Prolacerta broomi is considerably less closely related to Archosauriformes than was previously considered. DOI: https://doi.org/10.7717/peerj.11143 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-203067 Journal Article Published Version The following work is licensed under a Creative Commons: Attribution 4.0 International (CC BY 4.0) License. Originally published at: Spiekman, Stephan N F; Fraser, Nicholas C; Scheyer, Torsten M (2021). A new phylogenetic hypothesis of Tanystropheidae (Diapsida, Archosauromorpha) and other “protorosaurs”, and its implications for the early evolution of stem archosaurs. PeerJ, 9:e11143. DOI: https://doi.org/10.7717/peerj.11143 A new phylogenetic hypothesis of Tanystropheidae (Diapsida, Archosauromorpha) and other “protorosaurs”, and its implications for the early evolution of stem archosaurs Stephan N.F. Spiekman1, Nicholas C. Fraser2 and Torsten M. Scheyer1 1 University of Zurich, Palaeontological Institute and Museum, Zurich, Switzerland 2 National Museums Scotland, Edinburgh, UK ABSTRACT The historical clade “Protorosauria” represents an important group of archosauromorph reptiles that had a wide geographic distribution between the Late Permian and Late Triassic. “Protorosaurs” are characterized by their long necks, which are epitomized in the genus Tanystropheus and in Dinocephalosaurus orientalis. Recent phylogenetic analyses have indicated that “Protorosauria” is a polyphyletic clade, but the exact relationships of the various “protorosaur” taxa within the archosauromorph lineage is currently uncertain. Several taxa, although represented by relatively complete material, have previously not been assessed phylogenetically. We present a new phylogenetic hypothesis that comprises a wide range of archosauromorphs, including the most exhaustive sample of “protorosaurs” to date and several “protorosaur” taxa from the eastern Tethys margin that have not been included in any previous analysis. The polyphyly of “Protorosauria” is confirmed and therefore we suggest the usage of this term should be abandoned. Tanystropheidae is recovered as a monophyletic group and the Chinese taxa Dinocephalosaurus orientalis and Pectodens zhenyuensis form a new Submitted 1 September 2020 archosauromorph clade, Dinocephalosauridae, which is closely related to Accepted 2 March 2021 Tanystropheidae. The well-known crocopod and former “protorosaur” Prolacerta Published 3 May 2021 broomi is considerably less closely related to Archosauriformes than was previously Corresponding author considered. Stephan N.F. Spiekman, [email protected] Academic editor Subjects Evolutionary Studies, Paleontology, Zoology Claudia Marsicano Keywords Protorosauria, Tanystropheidae, Dinocephalosauridae, Archosauromorpha, Phylogeny, Additional Information and Triassic, Character matrix, Cladistics, Permian Declarations can be found on page 153 INTRODUCTION DOI 10.7717/peerj.11143 Non-archosauriform archosauromorphs lived during the late Permian and Triassic and Copyright belong to the archosaurian stem-lineage, the ancestral lineage of crocodylians and birds. 2021 Spiekman et al. Historically, many members of this group were placed within either “Protorosauria” or Distributed under “Prolacertiformes”. These two groups generally encompassed the same taxa and the usage Creative Commons CC-BY 4.0 of one term over the other depended on the inclusion within the clade of either Protorosaurus speneri or Prolacerta broomi, or both. Since both names generally apply to How to cite this article Spiekman SNF, Fraser NC, Scheyer TM. 2021. A new phylogenetic hypothesis of Tanystropheidae (Diapsida, Archosauromorpha) and other “protorosaurs”, and its implications for the early evolution of stem archosaurs. PeerJ 9:e11143 DOI 10.7717/peerj.11143 the same taxa and are often used interchangeably, and because “Protorosauria” Huxley, 1871 predates “Prolacertiformes” Camp, 1945, we refer to the members of these groups here as “Protorosauria” (sensu Chatterjee, 1986). Apart from the two above mentioned genera, the terrestrial and aquatic long-necked tanystropheids (e.g., Tanystropheus, Macrocnemus, Langobardisaurus, and Tanytrachelos) represent the most morphologically diverse and best-known members of “Protorosauria”. Formerly, the enigmatic arboreal drepanosaurids were also referred to the clade, but they have recently been revealed to represent a separate clade of non-saurian diapsids (Pritchard & Nesbitt, 2017; Pritchard et al., 2016). As Permo-Triassic non-archosauriform archosauromorphs, “protorosaurs” represent some of the earliest members of the lineage that gave rise to Archosauria and as such are important both for our understanding of early archosauromorph evolution and the acquisition of traits within the archosaur character complex. For instance, the Chinese Dinocephalosaurus orientalis and an unnamed closely related taxon represent the only known viviparous archosauromorphs (Li, Rieppel & Fraser, 2017; Liu et al., 2017). Recent cladistic studies have extensively dealt with early archosauromorph phylogeny (early Archosauria, Nesbitt, 2011; early Archosauromorpha with a focus on proterosuchians, Ezcurra, 2016; Allokotosauria, Nesbitt et al., 2015; Rhynchosauria, Butler et al., 2015 and Ezcurra, Montefeltro & Butler, 2016; and Tanystropheidae, Pritchard et al., 2015). These, and some earlier analyses, indicate that “Protorosauria” does not form a monophyletic clade as historically considered, but rather represents a paraphyletic or polyphyletic grouping of non-archosauriform archosauromorphs (Fig. 1, but for an exception see Simões et al., 2018, who recovered Protorosauria excluding Prolacerta as a monophyletic clade outside Archosauromorpha). However, none of these analyses were constructed to specifically address the interrelationships of “Protorosauria” and many recently described taxa (e.g., the genera Pectodens, Fuyuansaurus, Dinocephalosaurus, Raibliania, Elessaurus, and Sclerostropheus) attributed to the group or an equivalent grade in the archosauromorph tree have not been included (Dalla Vecchia, 2020; De Oliveira et al., 2020; Fraser, Rieppel & Li, 2013; Li et al., 2017; Rieppel, Li & Fraser, 2008; Spiekman & Scheyer, 2019). Moreover, the two best-known tanystropheid genera, Tanystropheus and Macrocnemus, were recently revised extensively, revealing much additional morphological information, particularly with regards to the skull, which has not been incorporated in the abovementioned analyses (Miedema et al., 2020; Spiekman et al., 2020a, 2020b). Here we present an extensive phylogenetic analysis, focusing on “protorosaur” and other non-archosauriform archosauromorph interrelationships. The new dataset includes 42 operational taxonomic units (OTUs), of which 23 are “protorosaurs”, and employs 307 morphological characters, many of which are new or distinctly revised from previous analyses. Since the definition of “Protorosauria” in the literature is inconsistent, with many taxa having been placed alternately within and outside the group, we first provide a historical overview of “protorosaur” systematics and discuss the taxa that have formerly been included in the group. Several of these are represented by very fragmentary material or have since been identified as belonging to an entirely separate lineage to that of the archosauromorph “protorosaurs”, and they were therefore not included in our phylogenetic analysis. Spiekman et al. (2021), PeerJ, DOI 10.7717/peerj.11143 2/174 Figure 1 Selected phylogenetic hypotheses for “protorosaur” relationships. (A) Ezcurra (2016). (B) Pritchard et al. (2015). (C) Rieppel, Fraser & Nosotti (2003), which represents a compilation of the matrices of Benton & Allen (1997), Jalil (1997), and Dilkes (1998). Full-size DOI: 10.7717/peerj.11143/fig-1 Spiekman et al. (2021), PeerJ, DOI 10.7717/peerj.11143
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