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Redescription of Anaschisma (Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the Phylogeny of the Metoposauridae

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Redescription of Anaschisma (Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the Phylogeny of the Metoposauridae University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln U.S. National Park Service Publications and Papers National Park Service 3-14-2019 Redescription of Anaschisma (Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the phylogeny of the Metoposauridae Bryan M. Gee University of Toronto Mississauga, [email protected] William G. Parker Petrified orF est National Park Adam D. Marsh Petrified orF est National Park Follow this and additional works at: https://digitalcommons.unl.edu/natlpark Part of the Environmental Education Commons, Environmental Policy Commons, Environmental Studies Commons, Fire Science and Firefighting Commons, Leisure Studies Commons, Natural Resource Economics Commons, Natural Resources Management and Policy Commons, Nature and Society Relations Commons, Other Environmental Sciences Commons, Physical and Environmental Geography Commons, Public Administration Commons, and the Recreation, Parks and Tourism Administration Commons Gee, Bryan M.; Parker, William G.; and Marsh, Adam D., "Redescription of Anaschisma (Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the phylogeny of the Metoposauridae" (2019). U.S. National Park Service Publications and Papers. 197. https://digitalcommons.unl.edu/natlpark/197 This Article is brought to you for free and open access by the National Park Service at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in U.S. National Park Service Publications and Papers by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Journal of Systematic Palaeontology, 2020 Vol. 18, No. 3, 233–258, http://dx.doi.org/10.1080/14772019.2019.1602855 Redescription of Anaschisma (Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the phylogeny of the Metoposauridae aà b b Bryan M. Gee , William G. Parker and Adam D. Marsh aDepartment of Biology, University of Toronto Mississauga, 3359 Mississauga Road, ON L5L 1C6, Canada; bDivision of Science and Resource Management, Petrified Forest National Park, 1 Park Road, PO Box 2217, AZ 86028, USA (Received 12 March 2018; accepted 14 March 2019) Metoposaurids are non-marine temnospondyls that are among the most common constituents of Late Triassic deposits, but despite their abundance, the evolutionary relationships of the group are poorly resolved and have not been fully addressed with modern phylogenetic methods. The genus Anaschisma is one of a number of poorly resolved metoposaurid taxa and was erected to describe two species from the Popo Agie Formation (Carnian) in Wyoming: Anaschisma browni and Anaschisma brachygnatha. Since being named, the genus has been repeatedly synonymized and separated with other taxa in the context of broader revisions of the Metoposauridae. At present, Anaschisma is considered to be an indeterminate metoposaurid. Extensive descriptive work of metoposaurids since the erection of Anaschisma in 1905 and the last taxonomic review of the clade in 1993, including the naming of several new taxa and the reappraisal of several others, has generated a sufficiently detailed database through which to re-evaluate the taxonomy of the Metoposauridae as part of the analysis of phylogenetic relationships of Anaschisma. Here we reappraise and redescribe the holotypes of A. browni and A. brachygnatha to determine their taxonomic status and relationships in the context of an updated and revised metoposaurid phylogenetic framework. Anaschisma browni and Anaschisma brachygnatha are synonymized under the former species, as all previously listed diagnostic differences are compatible with intraspecific variation. Additionally, the well-known Koskinonodon perfectus is found to be a junior synonym of Anaschisma browni, which takes taxonomic precedence given its earlier description. Poor phylogenetic resolution of the Metoposauridae is likely the product of marked morphological conservatism within the clade and limited character sampling, although some patterns of regional clustering are apparent from the analysis. Keywords: Anaschisma; Koskinonodon; Metoposauridae; Triassic; Popo Agie Formation Introduction interpretation of both taxa. Most significant of these was clarification that the otic notch region had been signifi- History of Anaschisma cantly damaged, with subsequent reconstructions giving Metoposaurids are typically large-bodied aquatic temno- the false appearance of a shallow otic notch (Branson & spondyls that are commonly recovered from Laurasian Mehl 1929). These authors maintained the taxonomic non-marine environments of the Late Triassic. The distinction between A. browni and A. brachygnatha. genus Anaschisma was erected by Branson (1905)to Romer (1947) suggested that it was highly likely that describe two new metoposaurid taxa, Anaschisma all of the forms described from the Popo Agie by browni and Anaschisma brachygnatha, from the Popo Branson & Mehl (1929) – Anaschisma browni, Agie Formation (Carnian) in Wyoming on the basis of Anaschisma brachygnatha, Koskinonodon princeps and cranial material. Since its inception, Anaschisma has Borborophagus wyomingensis (the latter two now syno- been the subject of extensive revision, often as part of a nymized under Koskinonodon perfectus) – were at least broader study of the Metoposauridae. In a study of the congeneric, and added that Buettneria (also a junior lateral line system in extinct amphibians, Moodie (1908) synonym of Koskinonodon (e.g. Mueller 2007)) might suggested that A. brachygnatha, the smaller of the two, be as well. Colbert & Imbrie (1956) reaffirmed the val- was a juvenile of A. browni and that many of the diag- idity and diagnosis of Anaschisma in their review of the nostic features were either the product of ontogeny (e.g. Metoposauridae, but they agreed with Moodie (1908)in width of skull) or intraspecific variation (e.g. orbit pos- considering A. brachygnatha to be a juvenile form of A. ition). A study of the holotype specimens by Branson & browni. Furthermore, based on morphometric analyses, Mehl (1929) made several revisions to the original they synonymized all four of the taxa from the Popo à Corresponding author. Email: [email protected] # The Trustees of the Natural History Museum, London 2019. All rights reserved. Published online 28 May 2019 234 B. M. Gee et al. Agie Formation (A. browni, A. brachygnatha, K. Anaschisma specimens and errors regarding the interpret- princeps and B. wyomingensis) under one species, ation of otic notch development have resulted in Eupelor browni, which was considered distinct from Anaschisma either being designated as synonymous with Eupelor durus of the Newark Supergroup and two sub- Ap. gregorii (e.g. Gregory 1980)orasanomen dubium species of Eupelor fraasi from the Chinle Formation (Hunt 1993). Hunt’s taxonomic designation for material and Dockum Group. Chowdhury (1965) further reduced of Anaschima has otherwise been maintained. the family in arguing that there were no morphological differences that distinguished the European History of metoposaurid phylogenetics Metoposaurus from the North American Eupelor and Metoposaurids have a long research history, dating back united all metoposaurids under the former genus, lead- to the description of Metopias diagnosticus by Meyer ing material formerly ascribed to Anaschisma to be (1842). Since then, at least 13 genera and 26 species lumped under Metoposaurus browni with a number of have been erected, many of which have since been syn- other taxa. onymized with other taxa or designated as nomina dubia Gregory (1980) agreed with Branson’s original inter- owing to the holotype material being too fragmentary to pretation of shallow otic notches in material of be diagnostic; the general history of Metoposauridae is Anaschisma as being valid, non-taphonomic features well summarized by Colbert & Imbrie (1956) and Hunt and revived the possibility of shallow otic notches as a (1993). At present, only six genera and nine species are taxonomically informative feature, leading to the restor- unequivocally accepted. Three of these occur in Europe, ation of Anaschisma and the assignment of a third spe- Metoposaurus diagnosticus (Meyer 1842), cies with a shallow otic notch from New Mexico to the Metoposaurus krasiejowensis (Sulej 2002, 2007) and genus, which he did not name. Several workers contin- Metoposaurus algarvensis (Brusatte et al. 2015), and ued the trend of assigning specimens from New two are known from Morocco, Dutuitosaurus ouazzoui Mexico with shallow otic notches to Anaschisma sp. and Arganasaurus lyazidi (Dutuit 1976). The Indian without formalizing a new species (e.g. Lucas et al. metoposaurid described as Metoposaurus maleriensis by 1985; Milner 1989; Murry 1989). Hunt (1989) finally Chowdhury (1965) is sometimes synonymized with distinguished the Popo Agie Formation metoposaurids Koskinonodon perfectus (e.g. Hunt 1993) or maintained from the New Mexico taxon on the basis of elongate as a separate species within Koskinonodon (e.g. intercentra and a lacrimal that does not contact the Sengupta 2002), but has most recently been assigned to orbital margin in the latter, which was formalized as a new genus, Panthasaurus (Chakravorti & Sengupta Apachesaurus gregorii by Hunt (1993). The brief gen- 2018). Lastly, three taxa are found in North America: eric association with Apachesaurus also led Anaschisma Koskinonodon perfectus, ‘Metoposaurus’ bakeri and to be briefly suggested to be a junior synonym of Apachesaurus gregorii (Hunt 1993;
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