THE PHYLOGENETIC PALEOECOLOGY OF DIPLOPORE BLASTOZOANS (ECHINODERMATA)

Incorporating phylogenetics into the study of paleoecology allows us to explore evolutionary drivers and examine past relationships between ecosystems and organisms. With phylogenetic paleoecology, morphological responses to environmental pressures can be evaluated to identify macroevolutionary modes and broader evolutionary responses to global change. Extinct echinoderms are excellent candidates upon which to test hypotheses of phylogenetic paleoecology–they are morphologically diverse and abundant across geologic time; further, many modern groups have been shown to respond morphologically to environmental changes. While many echinoderms - including the extant groups such as sea stars - are better studied in terms of their evolutionary pathways, blastozoans have been historically understudied and remain an area of active research. Recently, new phylogenetic analyses have been published on blastozoans, which opens opportunities to test hypotheses about evolutionary shifts in paleoecology. Diploporans (Ordovician – Devonian) are one such group of blastozoans; a recent phylogenetic analysis indicated that they are polyphyletic, making their defining feature, paired pore respiratory structures (diplopores), likely homoplastic. The reappearance of this trait could represent a response to changing ecology. In this study, we combine the updated phylogenetic tree of diploporans and ecological characteristics (e.g., bathymetry, substrate composition, and energy of deposition) from their paleoenvironments throughout the Paleozoic to determine evolutionary signal in paleoecological environment. Phylogenetic trees and habitat affinity determined from the ecological characteristics, both calculated using Bayesian methods, are evaluated for the strength of the phylogenetic signal of each trait. We investigate these features to fit diploporans into broader contexts of echinoderm ecology and evolutionary trends.