Morphological evolution during the last hurrah of the trilobites: Morphometric analysis of the Devonian asteropyginid trilobites

The Asteropyginae Delo, 1935, is a group of phacopide trilobites in the
family Acastidae Delo, 1935, that has served as the focus for several
studies due to their distinctive morphologies and diversity. However,
despite an interest in these characteristic morphologies, there have been
very few studies that have examined this group using morphometric
techniques. In this study, we have utilized both geometric morphometric
and elliptical Fourier (EF) methods to quantify the morphology of cephalic
sclerites of specimens representing a wide taxonomic sampling of the
clade. We constructed a phylomorphospace that shows temporal and spatial
patterns of phenotypic evolution within the framework of an updated
tip-dated phylogenetic tree generated using Bayesian inference. Of
particular note was the recovery of similar patterns, regardless of the
morphometric approach. These further illustrated that there were marked
expansions into morphospace throughout the temporal range of the clade.
This study highlights the utility of employing different methodologies to
quantitatively explore the disparity of fossil taxa. It also illustrates
some of the patterns of morphologic change occurring during one of the
final and major evolutionary radiations within Phacopida.