A Detailed View of Late Ordovician (Richmondian) Invader and Incumbent Faunas Within the Cincinnati Arch

The Richmondian Invasion refers to a series of Richmondian Age (Late Ordovician; Katian; 448–445 Ma) coordinated biotic events of marine invertebrates recorded in the extensive fossiliferous deposits of the Cincinnati region. Significant ecological impacts have been postulated utilizing faunal data with low resolution stratigraphy. This study employs a redefined higher resolution stratigraphic framework with the comprehensive dataset of W.H. Shideler to analyze the Richmondian Invasion. Incumbent or native diversity was shown to be consistent throughout the Richmondian with little evidence of extirpation or declining diversity. Unlike incumbents, invader diversity increased throughout most stratigraphic intervals. Significant increases in invader diversity and first appearances were observed in four distinct phases within the Arnheim, Waynesville (Clarksville), Liberty, and Whitewater formations. The Clarksville Member and Liberty Formation were considered major phases of invasion due to the persistence of the invading genera appearing within these phases. Moreover, the distribution of invaders and incumbents appear to be indicative of fluctuating environmental conditions. This study highlights the importance of contextualizing biotic events in the geologic past at a high stratigraphic resolution to increase accuracy of interpretations.