DIGITAL DRY DREDGING: REASSESSING EOBALANUS, RUEDEMANN'S "ANCESTRAL ACORN BARNACLE"

Digitization of scientific literature has radically expanded the research opportunities available to avocational paleontologists. Many heretofore rare publications are now indexed and searchable by anyone with an internet connection. Dedicated amateurs are key users of these resources, as 19th or early 20th century vintage papers are still the gold standard for fossil identification in some regions. These researchers occasionally encounter problematic taxa or anomalous observations noted in older works that can be reinterpreted in light of more recent advances.

One such example is Eobalanus Ruedemann, 1918, a problematicum described by New York State Paleontologist Rudolf Ruedemann from Upper Ordovician (Katian) strata in Oneida County, New York. Small and flat, these ovoid, twelve-plated fossils were found associated with the living chambers of nautiloid cephalopods. Ruedemann named two species: Eobalanus informans, from the Indian Castle Shale ("Utica Shale"), and Eobalanus trentonensis, from the limestones of the Trenton Group. He interpreted both as ancestral acorn barnacles in support of his phylogenetic hypothesis linking phyllocarids and balanomorphs. While this argument was soon challenged, the specimens received little subsequent study and remain problematic.

Reinspection of the Eobalanus informans type specimens confirms close agreement with Ruedemann's description and figures. In contrast, the poorly preserved Eobalanus trentonensis holotype is only dubiously similar to its illustration and, pending further study, should not be considered congeneric. An acorn barnacle affinity is rejected as current fossil evidence and molecular data indicate balanomorph origination in the Mesozoic. Rather, the twelve articulated triangular-to-trapezoidal plates of Eobalanus appear to correspond to the head, tail, and lateral plates of multiplacophoran mollusks (Mollusca: Polyplacophora: Multiplacophora). A multiplacophoran interpretation is significant as it extends the record of this chiton lineage from the Silurian (Wenlock) down into the Ordovician. However, several aspects of Eobalanus's plate morphology differ from other multiplacophorans, making this identification provisional until additional material is discovered.