The Geological Society of America, 2014

The Geological Society of America, 2014
Date: 19 – 22 October, 2014
Place: Vancouver, Canada

PRESENTATIONS and ABSTRACTS

1) Kammer, Thomas W. Early-stage post-larval crinoids from the lower Devonian Hunsrück Slate, Germany.

Several stemmed crinoids with crowns as small as 1 mm wide by 2 mm high are newly recognized from the Hunsrück Slate of southwestern Germany.

Some of these tiny crinoids have a stalk up to 4 mm long with a holdfast. The presence of erect arms distinct from the calyx is uncertain, but they may be tightly infolded. Taxonomic identification of these crinoids is not possible, even to the subclass level, although they are preserved with larger juveniles that are most likely the cladids Propoteriocrinus and Lasiocrinus. The larger juveniles exhibit pyritized calcite plates, whereas the tiny crinoids appear to be preserved as pyritized dermal tissues enclosing poorly-calcified ossicles. Although a rare type of preservation, pyritized soft tissues have been found in a wide variety of taxa in the Hunsrück Slate. Based on comparison with the size and gross morphology of developmental stages in living comatulid crinoids, these tiny crinoids are judged to be analogous to the pentacrinoid stage of development, just after metamorphosis from the stalked, but armless, cystidean larval stage. Living comatulid crinoids have three larval stages (the uniformly-ciliated and doliolaria stages, and the stalked cystidean stage) before reaching the pentacrinoid developmental stage defined by arm development. Final metamorphosis to the juvenile stage in comatulids is by autotomy of the stem resulting in a free-swimming adult form. Living stalked crinoids become juveniles after metamorphosis from the cystidean stage as there is no pentacrinoid larval stage ending with autotomy of the stem (however, little is known about post-doliolaria larval development in living stalked crinoids). These tiny Hunsrück crinoids are judged to be at this post-larval developmental stage after metamorphosing from the cystidean larval stage. These post-larval juvenile, crinoids are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely juveniles of adult crinoids (30 genera) present in the Hunsrück. Although similar in size, they are not thought to be paedomorphic adult microcrinoids, which lacked arms and apparently fed either by podia through open oral plates, or by direct absorption of nutrients through the epidermis.

2) Ausich, William I. Exploring phylogenic relationships among Ordovician crinoids.

Application of Universal Elemental Homology on stellate echinoderms has demonstrated that crinoids are nested within the blastozoans; thus blastozoans are used to root crinoids and test among competing hypotheses for the early divergence of crinoids. Phylogenetic analyses were run on 40 Tremadoc to Darriwilian (Ordovician) crinoids using more than 100 unweighted characters (in excess of 470 character states) with blastozoans as the outgroup. Analyses with taxa from only the Tremadocian to Floian and Tremadocian to Dapinigian were also completed. All analyses confirm five basic groupings of taxa: camerates, “normal” cladids, disparids, hybocrinids, and a grouping of cladids and other crinoids with non-standard plating. Relationships among these groupings indicate that camerates are basal from which cladids arose, and disparids and hybocrinids originated from within cladids. Contrasting analyses indicate that protocrinids were either primitive or more derived. Additional, separate analyses of Sandbian crinoids with well-preserved oral regions corroborate the basic crinoid groupings listed above. During their initial divergence crinoids experienced morphological experimentation leading to a significant amount of homoplasy before the morphological disparity among clades became more diagnostic for each group.