Triassic Isopoda – three new species from Central Europe shed light on the early diversity of the group Mario Schädel, TiMo van eldijk, herMan WinkelhorST, jelle W.F. reuMer & joachiM T. haug Despite its vernacular names (e.g. ‘woodlice’) Isopoda is a group with mostly aquatic species, with most species living in marine environments. The fossil record for isopods compared to other groups of Eucrustacea is relatively sparse. This applies even more for the Triassic. While in the Jurassic Isopoda is relatively well represented by fossils, only eight species have previously been described from the Triassic. In this study three new species of Isopoda are described from two field sites in Europe:Obtusotelson summesbergeri sp. nov. and Discosalaputium aschauerorum sp. nov. from Polzberg (Gaming, Lower Austria, Austria) and Gelrincola winterswijkensis sp. nov. from Winterswijk (Gelderland, Netherlands). All three new species are interpreted as representatives of Scutocoxifera (ingroup of Isopoda). The species Gelrincola winterswijkensis sp. nov. is further interpreted to be a representative of Cymothoida (ingroup of Scutocoxifera). Most of the oldest fossils of Isopoda belong to Phreatoicidea, which is supposed to be the sistergroup to all remaining Isopoda. Nowadays, Phreatoicidea is a small relic group, its representatives living in freshwater environments. The new species herein presented contribute to our understanding of the diversity of Isopoda in the Triassic and support the assumption that the transition from a dominance of Phreatoicidea towards the dominance of the remaining lineages of Isopoda happened quite early (likely prior to the Triassic). • Key words: fossil, morphometry, Scutocoxifera, Polzberg, Winterswijk. MARIO SCHÄDEL, TIMO VAN ELDIJK, HERMAN WINKELHORst, JELLE W.F. REUMER & JOACHIM T. HAUG 2020. Triassic Isopoda – three new species from Central Europe shed light on the early diversity of the group. Bulletin of Geosciences 95(2), 145–166 (7 figures, 4 tables, 1 appendix, 3 supplementary files). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received September 28, 2019; accepted in revised form February 26, 2020; published online May 16, 2020; issued May 30, 2020. Mario Schädel, Department of Biology II, Ludwig-Maximilians-Universität Munich, Großhaderner Str. 2, 82152 Planegg-Martinsried, Germany; [email protected] • Timo van Eldijk, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands • Herman Winkelhorst, Molenstraat 14, 7122ZW Aalten, The Netherlands • Jelle W.F. Reumer, Stratigraphy and Paleontology, Department of Earth Sciences, Utrecht University, Princetonlaan 8a, 3584 CB Utrecht, The Netherlands • Joachim T. Haug, Department of Biology II, Ludwig-Maximilians-Universität Munich, Großhaderner Str. 2, 82152 Planegg- Martinsried, Germany & GeoBio-Center of the LMU Munich, Richard-Wagner-Str. 10, 80333 Munich, Germany Isopoda is a large ingroup of the crustacean group Peracari- appendages (uropods) is dissimilar to that in many other da, comprising morphologically diverse representatives lineages of Isopoda by being styliform rather than flat. that inhabit a variety of ecosystems such as the deep sea, Extant representatives of Phreatoicidea are only found shores, brackish waterbodies, freshwater and one ingroup in freshwater environments (Wilson & Johnson 1999). even managed to inhabit terrestrial ecosystems (Wägele Phreatoicideans are also interesting, as the oldest fos sils of 1989, Brandt & Poore 2003, Broly et al. 2013). Even though Isopoda supposedly are representatives of this group. the majority of representatives of Isopoda can easily be The fossil record of the group Isopoda in the Palaeozoic recognised by the organisation of the body and the overall (see Tab. 1 for all described Palaeozoic species) can be shape, this does not necessarily apply for all groups. One denoted as rather scarce compared to the record in the of these groups is Phreatoicidea. Phreatoicidea is thought Meso- and Cenozoic. The oldest fossil record of the group to be the sistergroup to all remaining ingroups of Isopoda (Hesslerella shermani Schram, 1970) is from the Middle and is morphologically distinct in some aspects, including Pennsylvanian (Upper Carboniferous, about 300 million the overall shape (Wägele 1989, Brusca & Wilson 1991). years old) of Mazon Creek (Illinois, USA) and is interpreted Phreatoicideans are rather laterally compressed than dorso- as a representative of Phreatoicidea (Schram 1970). ventrally compressed, similar to sideswimmers (Amphipo - Five species have been described from the Middle Per- da; Nicholls 1942). Also the the shape of the posterior most mian of Brazil (Paraná Basin, São Paulo State; Mezzalira & DOI 10.3140/bull.geosci.1773 145 Bulletin of Geosciences • Vol. 95, 2, 2020 Table 1. Palaeozoic species of Isopoda. Species Age Country & reference Hesslerella shermani Schram, 1970 late Carboniferous, Moscovian Illinois, USA (Schram 1970) Sottyella montcellensi Racheboeuf et al., 2009 late Carboniferous, Gzhelian France (Racheboeuf et al. 2009) Pseudopalaega granulifera Mezzalira & Martins-Neto, 1992 early Permian, Artinskian Brazil (Mezzalira & Martins-Neto 1992) Pseudopalaega microcelata Mezzalira & Martins-Neto, 1992 early Permian, Artinskian Brazil (Mezzalira & Martins-Neto 1992) Pseudopalaega iratiensis Martins-Neto, 2001 early Permian, Artinskian Brazil (Martins-Neto 2001) Protourda tupiensis Mezzalira & Martins-Neto, 1992 early Permian, Artinskian Brazil (Mezzalira & Martins-Neto 1992) Protourda circunscriptia Mezzalira & Martins-Neto, 1992 early Permian, Artinskian Brazil (Mezzalira & Martins-Neto 1992) Palaeophreatoicus sojanensis Birstein, 1962 middle Permian Russia (Birstein 1962, Schram 1980) Protamphisopus reichelti Malzahn, 1962 late Permian, Lopingian Germany (Glaessner & Malzahn 1962) Palaeocrangon problematicus (= Prosoponiscus Germany (Schlotheim 1820, Schauroth 1854, late Permian, Lopingian problematicus) (von Schlotheim, 1820) Geinitz 1861) & Great Britain (Kirkby 1857) Martins-Neto 1992, Martins-Neto 2001, Chahud & Petri For the Triassic only eight species of Isopoda and one 2015), which are generally interpreted as representatives not formally described specimen have been reported so far of Scutocoxifera. Scutocoxifera is an ingroup of Isopoda, (Figs 1, 2). Anhelkocephalon handlirschi is deliberately not including Phreatoicidea, which representatives are not included, see discussion below. Records of the group characterised by having scale-like lateral expansions to the Isopoda are missing throughout the Early Triassic (Induan dorsal sclerites of the pereon (postocular segments 7–13) that and Olenekian). are part of the proximal leg element (‘coxal plates’) (Dreyer The earliest Triassic record, so far, is from the early Mid- & Wägele 2002). The remainder of the Palaeozoic fossils dle Triassic of France (‘Grès à Voltzia’ Formation, ‘Volt zien­­ of Isopoda have all been interpreted as representatives of sandstein’, Upper Buntsandstein, Anisian) with Pala ega Phreatoicidea (Glaessner & Malzahn 1962, Schram 1980). pumila Gall & Grauvogel, 1971 (Gall & Grauvogel 1971, A B Figure 1. Maps with the field sites of all published findings of Isopoda from the Triassic. • A – map of Europe. • B – world map. Stars denote field sites corresponding to the herein described fossils. 146 Mario Schädel et al.• Triassic Isopoda – three new species from Central Europe Figure 2. Temporal occurrences of Triassic fossils of Isopoda based on literature information and the new fossil records within this study. Scale in million years. The depicted time-spans (horizontal thick grey lines) do not refer to the longevity of the species, but to the temporal uncertainty of each occurrence. Abbreviations: Ind. – Induan; Jura. – Jurassic; Olen. – Olenekian; Perm. – Permian. Mader 1984, Gall & Grauvogel-Stamm 2005). Pala ega unlikely that it stems from the ‘Keuper’ (Erfurt Formation, pumila can be easily identified as a representative of Scu- Ladinian, Longobardian substage) since ceratids are to coxifera. Despite the generic name, no close relation - extremely rare in sediments of this age (Hagdorn 2015). ship to other species with the same (form-) genus name is Thus, more likely, the holotype of Isopodites triasinus generally assumed (Feldmann & Rust 2006). is from the underlying, older, limestones of the ‘Upper Protamphisopus wianamattensis Chilton, 1918 from Muschelkalk’ (Meissner Formation, Ladinian, Fassanian the Middle Triassic (Anisian) Ashfield Shale (Wiannamatta substage). The Fassanian can be correlated with an abso- Group, Sydney basin, Australia) is a phreatoicidean that lute age of ca. 241.5–239.1 million years (Ogg 2012), likely lived in a freshwater environment (Chilton 1918, consistent with the International Chronostratigraphic Wilson & Edgecombe 2003). Protamphisopus baii Fu Chart, v. 2019/5 (Cohen et al. 2013, updated). et al., 2010 from the Middle Triassic (Anisian) Luoping Isopodites triasinus has originally been interpreted as fauna (Guanling Formation, Yunnan Province, China) is a representative of the group Sphaeroma (Picard 1858); von also a representative of Phreatoicidea and likely lived in Ammon (1882) suggested a less specific interpretation and a marine environment (Fu et al. 2010, Hu et al. 2011). created a new generic name (Isopodites) for the species. From the Middle Triassic (Meissner Formation, Upper Due to the overall body shape, Isopodites triasinus has been Anisian)