Silurian lichid trilobites from northwestern Canada: Ontogeny and phylogeny of lichids

Abstract

Previously unknown ontogenies of five lichid genera, Dicranopeltis, Platylichas, Borealarges, Dicranogmus and Radiolichas, are described and placed in the context provided by a review of known lichid ontogenies. Lichid phylogenies have been based on holaspid morphology alone without reference to ontogeny. To broaden knowledge of lichid phylogeny, an analysis, based on the last protaspid instar of lichids and possible sister group taxa, is conducted. The results of this analysis show that, within the lichids, the traditional subfamily groupings are not supported, and the sister group of lichids is more likely to be found within the Proetida than the Odontopleurida. Tubercles, a prominent feature of lichid morphology, have not been considered taxonomically significant. An examination suggests that tubercle arrangement and the pattern of change of tubercle arrangement through ontogeny could be important in defining taxa. It is recommended that future work on lichid phylogeny include ontogenetic information and patterns of change in development.