EXPLORING THE DISTRIBUTION OF PARACRINOIDEA (ECHINODERMATA)

Quantifying distribution patterns of Paleozoic echinoderms can help researchers understand community structure, recognize biogeographic patterns, and understand why unusual morphologies persist. This has been done for other Paleozoic groups (e.g. blastoids and crinoids), but a lack of comprehensive study of paracrinoids, a small but important clade of blastozoan echinoderms, utilizing a rigorous phylogenetic and morphometric framework, has hindered their inclusion in such analyses.

Paracrinoidea is a small, temporally and spatially limited clade from the Middle to Late Ordovician of Laurentia and Baltica. The members of this group exhibit unusual morphologies, namely asymmetry in the position of the mouth and stem, asymmetrical ambulacra, and other features that are only shared by subsets of paracrinoid species. In addition to these unusual morphologies, the geographical distribution of paracrinoid species is incredibly disparate. Several species are especially abundant but are known from few outcrops, whereas other species are widely distributed but occur in relatively low abundance. Until recently, there was not a quantitative phylogenetic or morphometric analysis for paracrinoids; therefore, the temporal and spatial distribution patterns of paracrinoids could not be effectively studied.

Using an existing phylogenetic hypothesis and phylomorphospace for Paracrinoidea in conjunction with Principal Coordinates Analysis, we are able to examine which taxa are found in which localities, and more generally, which morphologies co-occur. Results demonstrate that approximately four localities have three or more species present, and that species at these localities exhibit a variety of morphologies. This study adds information on the distribution of paracrinoids and elucidates patterns regarding the morphologies present at each locality. This is paramount to our continued understanding of why such unusual morphologies presented themselves during the early Paleozoic.