A Unitary Association-based conodont biozonation of the Smithian-Spathian boundary (Early Triassic) and associated biotic crisis from South China Author Leu, Marc Paleontological Institute and Museum, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland Author Bucher, Hugo Paleontological Institute and Museum, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland Author Vennemann, Torsten Author Bagherpour, Borhan Author Ji, Cheng Author Brosse, Morgane Author Goudemand, Nicolas text Swiss Journal of Palaeontology 2022 19 2022-11-22 141 1 1 61 http://dx.doi.org/10.1186/s13358-022-00259-x journal article 10.1186/s13358-022-00259-x 1664-2384 PMC9681704 36439694 12000082 Genus HADRODONTINA Staesche, 1964 Type species. Hadrodontina anceps Staesche, 1964 . Type stratum and locality. Campiller member, Skyth , South Tirol , Italy . Remarks . Tere is still an ongoing debate about the phylogenetic relationships of Pachycladina , Parapachycladina and Hadrodontina . Sweet (1988) in his prioniodinid phylogeny considered Pachycladina and Hadrodontina as sister taxa. Some species of Pachycladina were assigned to a new genus Parapachycladina by Shunxin et al. (1997) , but this view is not widely accepted. Orchard (2007) observed that Hadrodontina anceps , Ellisonia aff. triassica and Pachycladina peculiaris appear to constitute a natural group, although they are currently assigned to different genera. Based on their cladistics analysis, Donoghue et al. (2008) concluded that Pachycladina is either a sister taxon to Ellisonia or stays unresolved in a polytomy with Ellisonia , Hadrodontina and Furnishius . Based on his multi-element apparatus reconstructions, Koike (2016) included Hadrodontina and Pachycladina within the subfamily Hadrodontinae ( Koike, 2016 ) , supporting the original view of Sweet (1988) . We follow here this suprageneric classification and include Hadrodontina and Pachycladina within the subfamily Hadrodontinae . More recently, Sun et al. (2020) published 3 natural assemblages of Hadrodontina aequabilis and confirmed the suprageneric classification of Koike (2016) . In P 1 elements, what most distinguishes Pachycladina from Hadrodontina is the basal configuration: the inverted basal ‘attachment’ surface of Pachycladina occupies the entire lower side plus one lateral side of the carina, whereas in Hadrodontina , a basal cavity with a deep basal groove is usually formed on the lower side and the attachment surface rarely extends over the mid-part of the keel, if at all. Te denticles of Pachycladina are also less numerous but much larger in relative size than those of Hadrodontina . Based on multi-element reconstructions however, Koike (2016) showed that Pachycladina peculiaris , as well as Ellisonia aff. triassica ( Koike et al., 2004 ) , should be synonymized with Hadrodontina aequabilis .