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Faunal turnover is a pattern of diversification and extinction that occurs in taxa throughout the geologic record. Patterns of repeated faunal turnovers are referred to as faunal progression. Understanding the driving factors behind faunal progression, which may be niche partitioning, competition between groups, movement to new environments, or extinction and radiation due to environmental factors, may be key to understanding the pasts and futures of our modern fauna. Within Decapoda, clawed lobsters, podotrematous crabs, and heterotrematous crabs experienced faunal progression. These groups diversified and faced high rates of extinction in succession. The transition between podotrematous crabs and heterotrematous crabs is the most recent such turnover and is therefore of particular interest when trying to understand the potential causes of decapod faunal progression as a whole. Section Raninoida, commonly called ‘frog crabs’, constitutes a major monophyletic group of crabs with podotrematous body forms, and closely follows broader trends of diversification and decline within the podotremes from the Cretaceous to the present day. Additionally, modern raninoids are highly specialized back burrowers, despite several extinct families displaying traits indicative of generalist lifestyles which would seem more likely to survive.Data on rock type, age, location, and carapace morphology for each species within section Raninoida were analyzed for trends in diversity, taxon longevity, paleoenvironment type, and paleogeographic occurrences using Microsoft Excel, Python, PAST, and ArcGIS. Paleomaps were generated to visualize type specimen occurrences and overall diversity through time.Declines in raninoid diversity aligned with mass extinction events and major climate shifts, especially those of cooling climate. Likewise, diversification within the section occurred in warm, greenhouse climates. Thus, a major factor in patterns of faunal turnover is likely to be environmental conditions. Raninoid families specializing in back-burrowing appeared to have survived the end-Cretaceous mass extinction event better than other families. However, generalist raninoid families did not go completely extinct at the end-Cretaceous yet failed to recover diversity in optimal climactic conditions as did specialist families. Given the diversification of heterotrematous crabs into a wide variety of niches throughout the Cenozoic, competition may be a secondary, but still crucial, factor in this faunal turnover. These findings help to illustrate the history of our modern decapod fauna and may aid in understanding similar patterns across other taxa.

The hypothesis of Coordinated Stasis, developed from observations of extended periods of faunal stability in Middle Devonian sediments of the Appalachian Basin, has been the topic of intense research in recent years in the field of paleoecology. Investigations into patterns of faunal persistence have been conducted on various sedimentary basins throughout the rock record; however no study has yet attempted to document concurrent faunal patterns in separate paleobiogeographic regions. The Middle Devonian Appalachian and Michigan basins provide a perfect test case for an examination of coeval patterns of faunal change as they were separate paleobiogeographic subprovinces at this time. Patterns of faunal turnover were examined in the Michigan Basin and compared to the well-documented record the coeval Appalachian Basin. In order to compare patterns at a fine scale, correlations between the Appalachian and Michigan Basins were refined using sequence stratigraphic criteria resulting in a high-resolution stratigraphic framework between the basins. It was possible to correlate both large- and small-scale sequences between the basins indicating the primary control on deposition across much of eastern North America was eustatic sea level oscillation. It was also possible to constrain the timing of tectonic activity between the basins as well as refine the biostratigraphy of the interval. Three separate faunal intervals were identified as having existed in the Middle Devonian in the Michigan Basin and were determined to be analogous to the Evolutionary Ecological (EE) Subunits of the Appalachian Basin Middle Devonian; the timing of faunal turnover between the EE Subunits was coeval between the basins. The degree of taxonomic mixing between the basins was also examined at the level of 3rd-order depositional sequence through the duration of the Hamilton-Traverse EE subunit using the Jaccard similarity coefficient indicating greater amounts of mixing between the basins at the beginning and end of the interval with more restricted mixing in the middle of the interval. Comparison of biofacies replacement through time was examined at a fine scale through a single 3rd-order sequence in the Appalachian Basin, the Michigan Basin, and an intermediate region using Detrended Correspondence Analysis yielding similar patterns through time in all areas.