An investigation of the Encrinurinae (Trilobita) by numerical taxonomic methods

Abstract

SynopsisNumerical taxonomic methods are applied to the Encrinurinae (Trilobita). Thirty-five cranidial and pygidial attributes are defined of which some (e.g. those relating to the glabellar tubercles) are specific to encrinurines and cybelines while others have application to non-encrinurids. Of nearly 200 named species of Encrinurinae only about one-third have been described in the literature in sufficient detail for their cranidial and pygidial attribute states be coded: a much smaller proportion of species is well enough known for librigenal, rostral, hypostomal and thoracic attributes to be coded. A comprehensive numerical taxonomy of the subfamily must therefore await detailed description of most of the known species. A list is given of encrinurine species in need of re-investigation. Meanwhile, 63 species can be coded for 34 attributes, and 75 species for 28 attributes. Principal components analysis is used to produce ordinations of these species. The minimal spanning tree superimposed on the ordination suggests possible evolutionary lineages. Ordination of the attributes is by non-linear mapping based on a distance matrix derived from the inter-attribute correlation matrix by the transformation (tanh−1|r|)−1. The ordinations compare well with subjective assessments of relations and phylogenies.