Hadrodontina, Staesche, 1964

Leu, Marc, Bucher, Hugo, Vennemann, Torsten, Bagherpour, Borhan, Ji, Cheng, Brosse, Morgane & Goudemand, Nicolas, 2022, A Unitary Association-based conodont biozonation of the Smithian-Spathian boundary (Early Triassic) and associated biotic crisis from South China, Swiss Journal of Palaeontology (19) 141 (1), pp. 1-61 : 53

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 .