During the early Katian (Late Ordovician), the North American craton was being inundated due to a major eustatic sea level rise and regional subsidence associated with the ongoing Taconic orogeny. The Trentonian brachiopod fauna, as a dominant group of the marine shelly benthos at that time, evolved and invaded the expanding epicontinental seas.
Three Trentonian brachiopod lineages were studied to trace their evolution. The Rostricellula-Rhynchotrema-Hiscobeccus lineage was characterized by an increase in shell size, globosity, and frilled lamellae, with Hiscobeccus becoming a prominent component of the Late Ordovician epicontinental brachiopod fauna.
Parastrophina is a widely reported but non-dominant taxon of the Trentonian brachiopod fauna in eastern North America. This study clarified details of the internal structures of the type species, P. hemiplicata, and quantified the high degree of intraspecific variability, particularly the development of ribs, fold, and sulcus. This has led to the recognition of Parastrophina tarimensis from northwest China as a new species.
Plectorthis is another key taxa of the Trentonian fauna, previously reported from several tectonic paleoplates. By examining the type species, P. plicatella, from the Cincinnati area in this study, the diagnostic characters of the genus were defined, which provided a basis for evaluating the North American and global distribution and diversity of this genus and a more accurate paleobiogeographic analysis.
Multivariate analyses of the Trentonian brachiopod collections from Manitoulin Island and the Lake Simcoe area in Ontario, in conjunction with other Trentonian faunas from North America, demonstrated that during the early stage of the Late Ordovician (early Katian) sea level rise and marine inundation of the continental interior, the epicontinental sea brachiopod fauna began to separate from the older pericratonic faunas. In Ontario, this is reflected by the brachiopod fauna of Lake Simcoe being more closely related to the Scoto-Appalachian fauna, and that of Manitoulin Island most similar to those in the intracratonic basins (e.g. Minnesota)
