Silurian Odontopleurinae (Trilobita) from the Cape Phillips Formation, Arctic Canada

Abstract

Odontopleurids are a diverse component of rich silicified trilobite faunas recovered from the Wenlock and Ludlow of the Cape Phillips Formation, central Canadian Arctic. Odontopleurinae and Acidaspidinae are common, but Ceratocephalinae and Koneprusiinae are also represented. This work treats all of the Odontopleurinae, with the exception of the genus Acanthalomina Prantl and Přibyl, 1949.New species of Kettneraspis Prantl and Přibyl, 1949, include the upper Sheinwoodian K. wrightae, the lower Homerian K. lindoei, and the Gorstian K. caldwelli. Rare specimens assigned to Odontopleura Emmrich, 1839, and Radiaspis Richter and Richter, 1917, occur in the Sheinwoodian of the central Arctic.Edgecombeaspis (type species E. johansonae new species) is proposed for an odontopleurine clade endemic to Laurentia, and in the Silurian restricted to northern Laurentia. Cladistic analysis yields a hypothesis of ingroup structure that is in general calibrated with stratigraphic sequence. An exception is a group of Telychian species from the Mackenzie Mountains, whose stratigraphic sequence was used to support a previous hypothesis of an ancestral-descendant lineage. The cladistic result indicates that the stratigraphic pattern is the inverse of the phylogenetic pattern: the stratigraphically lowest species in the proposed lineage is the most derived, and the highest is most primitive. In addition to the type, new species of Edgecombeaspis include the mid-Sheinwoodian E. jahansi and the lower Homerian E. soehni. Edgecombeaspis apparently became extinct in the Homerian.The species Kettneraspis lenzi (Chatterton and Perry, 1983) and Radiaspis cf. R. norfordi (Chatterton and Perry, 1983) occur in the central Arctic, and further strengthen previous correlations with strata in the central Mackenzie Mountains, Northwest Territories.