Cydonocephalus Whittington, 1963

Adrain, Jonathan M. & Pérez-Peris, Francesc, 2021, Middle Ordovician (Darriwilian) cheirurid trilobites from the Table Cove Formation, western Newfoundland, Canada, Zootaxa 5041 (1), pp. 1-73 : 22

Cydonocephalus Whittington, 1963

Type species. By original designation; Cydonocephalus griphus Whittington, 1963 , from the Shallow Bay Formation ( lower Darriwilian ) of western Newfoundland, Canada (Laurentia) .

Other species. Cheirurus mercurius Billings, 1865a , Shallow Bay Formation (lower Darriwilian), Newfoundland, Canada (Laurentia); Cheirurus prolificus Billings, 1865a , Shallow Bay Formation (lower Darriwilian), Newfoundland, Canada (Laurentia); Cydonocephalus prominulus Whittington, 1963 , Shallow Bay Formation (lower Darriwilian), Newfoundland, Canada (Laurentia); Cydonocephalus scrobiculus Whittington, 1963 , Shallow Bay Formation (lower Darriwilian), Newfoundland, Canada (Laurentia); Cydonocephalus tiffanyae n. sp., Table Cove Formation (Darriwilian), Newfoundland, Canada (Laurentia); Cydonocephalus torulus Whittington, 1963 , Shallow Bay Formation (lower Darriwilian), Newfoundland, Canada.

Possible species. Pseudosphaerexochus approximus Raymond, 1905 , Day Point Formation (Darriwilian), New York, USA (Laurentia); Pseudosphaerexochus chazyensis Raymond, 1905 , Day Point Formation (Darriwilian), New York, USA (Laurentia); Kawina divergens Reed, 1945 , Tourmakeady Limestone Formation (upper Floian), County Mayo, Ireland (Laurentian-affinity Northwestern Terrane); Kawina salebrosa Lisogor, 1995 , Karakan Formation (Darriwilian), Betpak-Dala Desert, Kazakhstan (Chu-Ili Terrane); K. sinica Zhou, Yin, and Zhou, 2014 , Yijianfang Formation (Darriwilian), Xinjiang, China (Tarim).

Discussion. Prior to this work, all of the named species of Cydonocephalus were from the pure white limestone boulder faunas of the lower Darriwilian part of the Shallow Bay Formation at Lower Head, western Newfoundland (Whittington, 1963). The only specimens known from elsewhere were a single cranidium from the Floian of the Valhallfonna Formation, Svalbard, arctic Norway, illustrated by Fortey (1980, p. 85, pl. 18, figs 13, 14) as “ Cydonocephalus sp. A ” and several silicified cranidia and pygidia from the Dapingian of the Sunblood Formation, Northwest Territories, Canada, illustrated by Tremblay and Westrop (1991, p. 820, fig. 16.37–16.47) as “ Cydonocephalus cf. C. torulus .”

Adrain and Fortey (1997, p. 92) proposed the synonymy of Cydonocephalus with Kawina , considering that it was “not possible to specify synapomorphic characters that would distinguish the two genera as separate monophyletic groups.” In the interim, however, data from species known from silicified faunas (herein, but also work in progress on the Antelope Valley Formation, California, and the Kanosh Formation, western Utah) suggest that Kawina should be restricted to a set of species sharing multiple cephalic and pygidial features (see below), none of which are shared with species previously assigned to Cydonocephalus . Hence, we recognize the latter genus, though work will be required to assess its structure and inclusivity. This we defer to a forthcoming revision of all of the original Newfoundland species described by Whittington.

There is a handful of mostly Middle Ordovician species, some not well known, that are clearly acanthoparyphines but definitely not Kawina and of questionable relationship to the type species of Cydonocephalus . We list them as potential species for the time being. Included in this group is Kawina divergens Reed, 1945 , from the Floian Tourmakeady Formation ( Adrain and Fortey, 1997), which has unusually smooth sculpture, strongly impressed glabellar furrows with a nearly fully isolated L1, and a pygidium with broad, subquadrate spines that are not in contact with one another in their distal half. When some of the other species become better known, or others are discovered, species like this may best be assigned to new genera. Pseudosphaerexochus approximus Raymond, 1905 , is known from two incomplete cranidia ( Shaw, 1968, pl. 12, figs 39–42), as is P. chazyensis Raymond, 1905 ( Shaw, 1968, pl. 13, figs 3, 4, 8, 9). Both are from the Darriwilian Day Point Formation. Both are obviously acanthoparyphine, but much more information would be required to meaningfully assess either. Kawina salebrosa Lisogor, 1995 , is based on a single incomplete cranidium. It does not appear to represent Kawina as restricted herein but is otherwise difficult to interpret. Finally, Kawina sinica Zhou, Yin, and Zhou, 2014 , is similar to K. divergens in that it is a reasonably well known species that lacks an obvious genus assignment in the current state of knowledge. It has subdued sculpture and a forwardly expanding glabella with a relatively low sagittal profile, features, as noted by Zhou et al. (2014, p. 109) with no obvious close comparisons in the group. Along with these named species are quite a few others described from various times and places in open nomenclature, some of which are as well or better known than some of the named taxa (e.g., Kawina sp. of Zhou et al. [2014, fig. 53A–F]).