A PHYLOGENETIC FRAMEWORK FOR THE SUBORDER AGNOSTINA

Agnostina is a moderately diverse group of arthropods comprised of at least 12 recognized families and over 100 genera that span the middle Cambrian to the Late Ordovician. The conserved morphologies of these enigmatic organisms and their lack of reliable diagnostic characters result in an unstable systematic classification and difficulty in testing phylogenetic relationships between ingroup taxa. A total of 51 taxa from 11 agnostine families, including some taxa that currently lack formal classification, were coded for a set of 82 characters that describe the range of morphological variation within the suborder. While Bayesian methods are becoming commonplace in paleontological investigations, there is a dearth of studies that use these probabilistic methods to explore relationships in entirely extinct clades. The fossilized birth-death (FBD) process allows for a more realistic tree model that incorporates aspects of paleontological data such as estimations of speciation and extinction dynamics, preservation, and sampling as a set of priors. In this study, I propose an MCC tree for Agnostina that shows strong crownward posterior support, reaffirming the majority of currently recognized taxonomic families with the notable exception of Pseudagnostidae. This tree provides a framework for continuing research into developmental constraints that may shape macroevolutionary patterns in this biostratigraphically important group of arthropods.