Ecological revolution of Oklahoma's rhynchonelliform brachiopod fauna during the Great Ordovician Biodiversification Event

Abstract

During the Great Ordovician Biodiversification Event (GOBE), the number of marine invertebrate families more than tripled. Fundamental shifts in clade dominance and ecological structure led to the rise of the Palaeozoic Fauna and the second Palaeozoic Ecological Evolutionary Unit (EEU P2 of Sheehan), which revolutionized benthic ecosystems for the next 200 million years. Although general global signals of increased diversity and ecosystem restructuring are known, direct links between these changes are more poorly constrained on high‐resolution local scales. To address this, rhynchonelliformean brachiopod assemblages of the Middle Ordovician Simpson Group (Oklahoma, USA) were assessed before, during and after maximum local diversity increase related to the second global pulse of the GOBE. Stratigraphically constrained brachiopod species occurrence and abundance data were collected for Dapingian‐lower Sandbian strata via field study. Brachiopod assemblages exhibited declining dominance and increasing evenness from the Dapingian through middle Darriwilian stages followed by high volatility in index values during and after the GOBE interval. These patterns document local faunal turnover and shift from EEU P1 to P2. Furthermore, the average species body volume statistically increased over this interval, a pattern that is independent of phylogenetic constraints. Paired increase in mean body size and size disparity is evidence of niche specialization and utilization of additional food resources. Together, changes in body size, evenness and dominance indicate that increasing ecological complexity was coincident with diversification in Oklahoma. This suggests that a common mechanism, such as climate optimization or increased food abundance, was locally responsible for building both taxonomic diversity and ecological complexity during the GOBE.

Late Sandbian (Sa2) radiolarians of the Pingliang Formation from the Guanzhuang section, Gansu Province, China

“…Remarks.-Hitherto, generic classifications of members of the Inaniguttidae are based on a wide range of morphological features, including the number of spines, number of spheres, spacing between spheres, and their dimensions (Caridroit et al, 2017;Noble et al, 2017). The significance assigned to each of these aspects is still debated because some authors question their reliability after considering factors such as ontogeny and ecological stress (Noble and Aitchison, 1995;Danelian and Popov, 2003;Suzuki, 2006;Maletz, 2011;Trubovitz and Stigall, 2018;Kachovich and Aitchison, 2020). Micro-CT observation reveals the genus Geminusphaera n. gen. shares characteristics intermediate between Inanihella and Inanibigutta.…”

Evolution of Ordovician cephalopod diversity in the Middle Yangtze region of South China and its controlling factors

“…Therefore, the evolution of the diversity of various groups might have been correlated to a certain extent. Brachiopod radiation known in the Northeastern Spitsbergen Region and in south-central Oklahoma in North America began in the Upper Floian and Lower Darriwilian (Hansen and Holmer 2010;Trubovitz and Stigall 2018). This seems to explain the low diversity of Early Ordovician cephalopods in Laurentia.…”

Contextualizing the Onset of the Great Ordovician Biodiversification Event

“…Trubovitz & Stigall () investigate the GOBE and its effects in the Ordovician successions of Oklahoma. Changes in body size, evenness and dominance suggest that increasing ecological complexity was coincident with taxonomic diversification in the Oklahoma succession.…”