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Abstract Geometric morphometrics facilitates the quantification and visualization of variation in shape and proportion through the comparison of homologous features. Eublastoidea, a Paleozoic echinoderm clade with a conservative body plan, is an ideal group for morphometric analysis, because their plate junctions are homologous and identifiable on all species. Eublastoids have previously been grouped taxonomically by generalized shape types (e.g., globose). These shapes are often used in taxonomic descriptions and as characters in phylogenetic analyses. The underlying homology of these broad shape types has never been explored. Herein we apply the first comprehensive use of three-dimensional geometric morphometrics (3D GMM) on fossil echinoderms to investigate taxonomic assignments, temporal distribution, and whether the varying proportions of skeletal elements that produce the gross thecal morphology are distinguishable. Taxonomic assignments specifically at the ordinal and family levels show varying amounts of overlap in morphospace, suggesting that many assignments may not be reevaluated. Our results suggest that none of the generalized shape types are distinct in morphospace and, therefore, likely do not capture the homologous changes in taxa. The plate circlet ratios showed trends specifically relating to the deltoid plate circlet, which has the most variability. We reanalyzed previous work and subsetted our data to be more comparable and found that there are key differences between methodologies and landmarks that will require future evaluation. Applying modern technological methods to previously explored questions allows for an updated understanding of this important fossil clade and provides a framework for others to assess fossil clades in a similar manner. 

Abstract Great strides have been made in understanding the phylogeny of the five extant echinoderm classes, however, many Palaeozoic groups have yet to be examined in a rigorous, quantitative framework. The aberrant morphologies of Paracrinoidea, an unusual group of Palaeozoic echinoderms, have hindered their inclusion in large‐scale phylogenetic and morphologic studies. This study uses a combined approach of phylogenetic analysis and morphological disparity to elucidate species relationships within the clade. Findings from this study suggest that Paracrinoidea is a monophyletic group and that respiratory structures, oral plate arrangement, and ambulacral morphologies are important for defining subclades within Paracrinoidea. Examination of paracrinoids in a quantitative framework, facilitates their inclusion in larger projects examining Palaeozoic echinoderm evolution, ecology and biogeography. 

The Paleozoic Era was host to many significant biotic events such as the Great Ordovician Biodiversification Event, the Late Ordovician Mass Extinction, and the Late Devonian extinctions. These events were likely catalyzed by abiotic (e.g. climate) versus biotic drivers. Echinoderms are globally distributed, temporally expansive, and easily identifiable; these qualities make them an excellent model system to test hypotheses relating biodiversity with abiotic factors. Biodiversity patterns of echinoderms are currently not well understood because of a lack of focus on the dynamics of the entire clade. To remedy this, we have worked to expand current understandings of Paleozoic echinoderm diversity patterns by investigating the global distribution and temporal occurrences of taxa spanning the entire clade. Results suggest patterns of diversity unique to previously established trends that predominantly centered on a limited number of echinoderm groups. To examine the connection between climate change and Paleozoic echinoderm biodiversity (i.e., diversification, extinction, and origination rates), we collated stable oxygen isotope data from the primary literature spanning the Ordovician to the Devonian. We compiled these data to create a continuous curve of δO values during the described period to better evaluate in tandem with echinoderm diversity metrics. When the δO curve is compared to the echinoderm biodiversity patterns, we found that cooling periods coincide with increased extinction rates, corroborating prior hypotheses that major end-Ordovician cooling triggered changes in echinoderm biodiversity at a global level and further identifying a potential pattern in abiotic drivers in echinoderm biodiversity. The connection between Paleozoic echinoderm biodiversity and other abiotic factors will be further studied by comparing these recovered patterns with paleolatitudinal distributions.