Phylogenetic placement of pelican spiders (Archaeidae, Araneae), with insight into evolution of the "neck" and predatory behaviours of the superfamily Palpimanoidea.

Abstract

Phylogenetic relationships among archaeid spider lineages, as well as the placement of archaeids within the Araneomorphae, present a problem in the systematics of spiders. We investigate these relationships by broadly sampling taxa from the Araneomorphae and superfamily Palpimanoidea, as well as from extant and fossil archaeid lineages. Using parsimony and Bayesian methods we perform a total-evidence analysis that includes 126 morphological characters and over 4000 bases from one mitochondrial and three nuclear molecular markers. Phylogenetic analysis results in a delimitation of the superfamily Palpimanoidea to contain five families: Archaeidae, Mecysmaucheniidae, Stenochilidae, Palpimanidae and Huttoniidae. We also find the extant archaeids, which are restricted to the southern hemisphere, to be monophyletic, with the fossil archaeids paraphyletic. This phylogenetic framework is then used to interpret a novel morphological character, the highly modified and elevated cephalic area and elongated chelicerae (jaws), coupled with prey choice observations in the field and observations of chelicerae movements during predatory attacks. We conclude that the evolution of the elevated cephalic area, which reoriented the chelicerae muscles, led to highly manoeuvrable chelicerae and associated novel prey capture strategies. All members of Palpimanoidea appear to have modifications to the cephalic area, such as a diastema or sclerotization around the chelicerae bases, and furthermore, members appear to have evolved prey specialization.