Systematics of the Acanthoparyphinae (Trilobita), with Species from the Silurian of Arctic Canada

Cladistic analysis of the trilobite subfamily Acanthoparyphinae Whittington and Evitt, 1954, yields an explicit hypothesis of relationship for the group. All Silurian species together form a robustly supported monophylum including the genera Hyrokybe Lane, 1972, Parayoungia Chatterton and Perry, 1984, and Youngia Lindström, 1885. Sister to this is the Ordovician type species of Acanthoparypha Whittington and Evitt, 1954. Remaining species that have historically been assigned to either Acanthoparypha or Pandaspinapyga Esker and Levin, 1964, form a rather labile paraphylum. Nevertheless, the entire group thus identified is definitely monophyletic, and supported by several prominent synapomorphic character-states. The basal structure and basal node of the subfamily are more difficult to assess. The relationships of the genera Hammannopyge Přibyl, Vaněk, and Pek, 1985, Holia Bradley, 1930, and Nieszkowskia Schmidt, 1881, need to be addressed within the wider context of the family as a whole. The traditional assignment of Holia to the acanthoparyphines is followed. Wenlock acanthoparyphines from the Cape Phillips Formation of the central Canadian Arctic islands include several species of Hyrokybe and Parayoungia. They are similar to, and in one case conspecific with, coeval forms to the southwest in the southern Mackenzie Mountains. Five species are new: Holia glabra, Hyrokybe lightfooti, Hyrokybe youngi, Hyrokybe mitchellae, and Parayoungia mclaughlini. At least four other potentially new species are reported in open nomenclature.