Geologic Drivers of Late Ordovician Faunal Change in Laurentia: Investigating Links between Tectonics, Speciation, and Biotic Invasions

Abstract

Geologic process, including tectonics and global climate change, profoundly impact the evolution of life because they have the propensity to facilitate episodes of biogeographic differentiation and influence patterns of speciation. We investigate causal links between a dramatic faunal turnover and two dominant geologic processes operating within Laurentia during the Late Ordovician: the Taconian Orogeny and GICE related global cooling. We utilize a novel approach for elucidating the relationship between biotic and geologic changes using a time-stratigraphic, species-level evolutionary framework for articulated brachiopods from North America. Phylogenetic biogeographic analyses indicate a fundamental shift in speciation mode—from a vicariance to dispersal dominated macroevolutionary regime—across the boundary between the Sandbian to Katian Stages. This boundary also corresponds to the onset of renewed intensification of tectonic activity and mountain building, the development of an upwelling zone that introduced cool, nutrient-rich waters into the epieric seas of eastern Laurentia, and the GICE isotopic excursion. The synchronicity of these dramatic geologic, oceanographic, and macroevolutionary changes supports the influence of geologic events on biological evolution. Together, the renewed tectonic activity and oceanographic changes facilitated fundamental changes in habitat structure in eastern North America that reduced opportunities for isolation and vicariance. They also facilitated regional biotic dispersal of taxa that led to the subsequent establishment of extrabasinal (=invasive) species and may have led to a suppression of speciation within Laurentian faunas. Phylogenetic biogeographic analysis further indicates that the Richmondian Invasion was a multidirectional regional invasion event that involved taxa immigrating into the Cincinnati region from basins located near the continental margins and within the continental interior.

Pathways and mechanisms of Late Ordovician (Katian) faunal migrations of Laurentia and Baltica

“…Wright & Stigall 2013) and the idea that separate pulses of the Richmondian Invasion had distinct source areas. Specifically, PAE results indicate a counter-clockwise shift in migration routes between the C2 and C5 sequences.…”

“…This transgression could have flooded intracratonic arches and facilitated dispersal between geographically separated areas (Wright & Stigall 2013), such as the basins in Cincinnati, the Upper Mississippi Valley and north of the Transcontinental Arch regions.…”

“…Contrastingly, Jin (2001) proposed that at least some invaders originated in cool-water marginal basins around Laurentia and immigrated into the Cincinnati region as part of the broader Hiscobeccus expansion. Wright & Stigall's (2013) phylogenetic analyses of brachiopods that participated in the Richmondian Invasion identified multiple geographic source regions within Laurentia, including both a marginal basin and western epicontinental basin. Bauer & Stigall (2014) reported support for the Artic pathway as well as the pathways of Wright & Stigall (2014).…”

Relating environmental change and species stability in Late Ordovician seas

“…Phylogentic data indicate that invaders were sourced from several geographic regions within Laurentia, including both peripheral and central basins (Wright & Stigall 2013) (Fig. 1).…”

“…Study region was located 208 to 258 south of the paleoequator. Red arrows indicate established pathways of migration during the Richmondian Invasion followingWright & Stigall (2013); additional migration routes may have operated. Base map afterBlakey (2011).…”