Crinoid Conundrum: Analysis of Disarticulated Crinoid Columnals from Mineral Wells, Texas.

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Authors:

Abstract:

Crinoids are an extant group of animals from the phylum Echinodermata. The crinoidea have a calyx, pelma, and holdfast. Traditional approaches to species-level diagnosis require the calyx. The large number and diversity of columnals has been recognized, but is rarely discussed as a diagnostic indicator for species. Moore and Jeffords (1968) presented a comprehensive evaluation of crinoid columnals that included their potential use in species-level diagnosis from Pennsylvanian strata in North America (the Midcontinent and Appalachian Basins, NM, and TX). To assess the diversity of Pennsylvanian crinoid columnals and evaluate their potential taxonomic value, a collection of crinoid columnals from the Mineral Wells Fossil Park (Palo Pinto County, Texas) has been imaged, described, and measured. There are three major columnal morphological groups (pentagonal, circular with petal lumens, and circular with circular lumens). Five separate diameters were measured matching the five-fold symmetry of the pentagonal columnals for all morphology groups to allow for valid comparison. The longest diameter was used for comparison. Each group was measured for columnal thickness, columnal diameter, columnal surface area, areola diameter, and lumen diameter. In the pentagonal group, two trendlines for columnal diameter versus columnal surface area were observed. These two trends could result from two different growth series; favoring two species or a single species in which a subset of specimens has been deformed or originates from other parts of the crinoid (cirri, holdfast, or arms). The circular lumen group plots on the same growth curve as the pentagonal group, suggesting they may be the same species with multiple columnal types. Similarly, the petal lumen group plots on the same trend. When plotting areola diameter versus columnal surface area, three groupings with distinct trendlines can be observed for larger specimens that corresponds to the morphological grouping. Many columnals from the Fossil Park appear deformed and they too were measured for comparison. In all cases, the trendlines shifted to higher columnal and areola diameters versus surface area. Trendlines for these misshapen columnals are less constrained than those of the undeformed columnals. These columnals likely do not represent different morphology groups, rather are likely the result of post depositional deformation.