Ichnotaxonomic Revisions to Trace Fossils in Echinoderm Substrata from the Silurian Massie Formation of Southern Indiana Paper

Abstract

Several ichnofossils emplaced within stalked echinoderm substrata have been described and figured from the middle Silurian Massie Formation of Ripley County, southeastern Indiana. Reconsideration and reinvestigation of figured and studied material resulted in the need for several ichnotaxonomic corrections. Most importantly, figured biogenic structures in the calyx of the crinoid Eucalyptocrinites and several pelmatozoan pluricolumnals were originally described as the bioerosional ichnogenus Trypanites, but actually belong to the ichnogenus Tremichnus, a parasitic embedment structure. Both relatively typical examples of Tremichnus paraboloides and T. paraboloides var. “minutus” are present. This shifts the timing of ichnofossil generation from post mortem to syn vivo within the echinoderm hosts and also helps explain why certain bioclasts were not bioeroded. In addition, several examples of the ichnospecies Tremichnus cystoidiphilus in holocystitid diploporitan hosts were discussed and figured. These are now also considered representatives of Tremichnus paraboloides, as T. cystoidiphilus is no longer recognized as a valid ichnotaxon. This not only corrects some ichnologic misidentifications, but also amends the list of ichnotaxa documented from the Massie Formation, as Trypanites is not present and Tremichnus cystoidiphilus no longer exists as an ichnospecies.