Silurian graptolites of the genus Cyrtograptus from the Cape Phillips Formation, Canadian Arctic Archipelago, Nunavut

Silurian graptolites of the genus Cyrtograptus have been collected from six sections of the Cape Phillips Formation on Cornwallis, Baillie-Hamilton, and Bathurst islands in the Canadian Arctic. Temporally, the collections span the entire range of their existence from the latest Telychian (Llandovery) to the end of the Lower Homerian (Wenlock).; Twenty-eight species of Cyrtograptus, including six new species, have been described and illustrated, the largest diversity recognized to date. Their stratigraphic distribution encompasses seven Cyrtograptus-based graptolite biozones: the C. sakmaricus and C. insectus biozones from the Upper Llandovery and the C. centrifugus, C. murchisoni , C. kolobus, C. perneri, and C. lundgreni biozones from the Wenlock. These biozones can be correlated with the generalized graptolite zonation and other sequences worldwide.; Cladistic analysis indicates that the cyrtograptid graptolites comprise a monophyletic clade based on the possession of thecal cladia. Torquigraptus flagellaris may be the most closely related representative of an ancestral form for the Cyrtograptus clade.; Cyrtograptid evolution consisted of three pulses of radiation that were affected by three extinction events. The third event resulted in the apparent total extinction of Cyrtograptus.; There was a trend towards decreasing provincialism from the C. sakmaricus through C. centrifugus - C. murchisoni biozones. Extreme provincialism existed in the superjacent mid-Wenlock C. kolobus Biozone, an interval in which cyrtograptids were generally absent elsewhere in the world. Finally, a decrease in provincialism and a trend toward cosmopolitanism was manifested in the Upper Wenlock C. perneri and C. lundgreni biozones.; All described species of Cyrtograptus have been recovered from the somewhat shallower, marginal regions of the Cape Phillips Embayment, whereas the more basinal region of the embayment was largely occupied by cosmopolitan species. The cosmopolitan species appear to have occupied an ecological niche different from that of the endemic species and this may have aided in their dispersal. These observations suggest that cyrtograptid provincialism may have been paleoecological in nature rather than paleogeographical.; The genus Cyrtograptus is retained in the Monograptidae. The genera Averianowograptus and Kurganakograptus are considered to be junior synonyms of the genus Cyrtograptus.