Early−Middle Devonian brachiopod provincialism and bioregionalization at high latitudes: A case study from southwestern Gondwana

Abstract

The paleobiogeography of Early−Middle Devonian (Pragian−Eifelian) brachiopods from West Gondwana was assessed to determine any potential controls (regional climatic differences or global eustasy) that may have driven bioregionalization. The Pragian−Eifelian interval of West Gondwana was examined because work by previous authors suggested that this was a period when regionally extensive areas of provincialism among marine invertebrates were present and most pronounced. Factors of particular interest in this study were the controls over brachiopod bioregionalization at high (60°−90°) southern latitudes, which the Malvinokaffric Realm is thought to have entirely occupied. A large presence-absence data matrix was compiled consisting of the occurrences of 206 genera from 17 localities across West Gondwana, and an array of multivariate methods (cluster analysis, nonmetric multidimensional scaling, and network analysis) was employed to assess regional bioregionalization trends. The results of our study suggest that regional climatic differences brought on by latitudinal effects were the determining driver for bioregionalism of brachiopods during the Pragian−Eifelian, and these trends were coincident with a global cooling period during the Early−Middle Devonian. Our study further suggests that of the three regional paleobiogeographic realms thought to be present in West Gondwana during the Early−Middle Devonian (Eastern Americas, Old World, and Malvinokaffric), only the Malvinokaffric Realm is valid as a single biogeographic area. Its area, however, is reduced; it is interpreted to have been a second-order biogeographic area and not a first-order area as suggested by previous authors. Given these factors, we suggest a new demonym for this area, the “Malvinoxhosan,” given the racially charged connotations of “Malvinokaffric.” We present a new biogeographic framework for West Gondwana that is free of preconceived biogeographic area and rank biases, with the understanding that a more globally expansive study should be undertaken to elucidate these areas and their rank within the correct hierarchy. Two first-order paleobiogeographic areas are recognized in West Gondwana and are named according to their latitudinal extent, namely, the high-latitude (60°S−90°S) and temperate-latitude (30°S−60°S) bioregions. The temperate-latitude bioregion consists of a single second-order paleobiogeographic area, the “Colombian−West African” bioregion. Two second-order bioregions are present in the high-latitude bioregion, namely, the Amazonian and Malvinoxhosan bioregions. Here, the Amazonian (∼50°S−70°S), compositionally, was an intermediate region between the Colombian−West African (∼30°S−50°S) and Malvinoxhosan (70°S−90°S) end members. Latitudinal effects may also have been responsible for dividing the Malvinoxhosan bioregion into two tentative third-order paleobiogeographic areas, namely, the Andeo−South African (∼70°S−80°S) and the Paraná (∼80°S−90°S) bioregions.

A natural history of networks: Modeling higher-order interactions in geohistorical data

“…Varying Markov time models can be used to explore structure and dynamics in both first- and higher-order networks (Kheirkhahzadeh et al 2016). These models are especially useful when the modular structure of an empirical network does not show a hierarchical organization (e.g., Penn-Clarke and Harper 2020) or when a two-level solution is chosen in the Map Equation framework. Exploring varying time scales to reveal fine to coarse partitions allows to connect time scales of the dynamics to the structural scales present in the network (Lambiotte et al 2014).…”

“…Research employing network-based approaches to describe biogeography in the fossil record is overwhelmingly focused on describing one-step dynamics (Markov time = 1) in relatively small bipartite networks derived from the relatively limited fossil data (e.g., Penn-Clarke and Harper, 2020; Ye et al, 2021), to reveal continental to global scale marine bioregions. Although first-order network representations of fossil occurrences have been shown to capture a biogeographic signal at some geological stages in the Phanerozoic (Rojas et al 2017; Kocsis et al 2018), these studies are unable to identify transition zones, provide a single-scale description of the bioregions and obscure larger-scale patterns.…”

“…This case study is based on a standard bipartite network that is relevant for Devonian biogeography, but the approach can be applied directly to higher-order networks. We use varying Markov time models to examine the bioregionalization of the Middle Devonian Brachiopods from the Old-World Realm (Penn-Clarke and Harper 2020). This approach allows to reveal the larger-scale biogeographic structure at different resolutions (Kheirkhahzadeh et al, 2016).…”

“…Bioregionalization of the Middle Devonian Old World Realm. A. Varying Markov time models on the biogeographic network constructed from the brachiopod data in Penn-Clarke andHarper (2020). Network partitions at different Markov times reveal the larger-scale biogeographic structures obtained at different resolutions.…”

Schellwienella clarkei (Orthotetida, Brachiopoda): a new species from the Devonian of the Paraná Basin, Brazil

“…We propose a systematic re-evaluation of the Malvinokaffric Realm (now called Malvinoxhosan Realm by Penn-Clarke and Harper, 2020) species “ Schuchertella ” agassizi through the descriptions of specimens from the Ponta Grossa and São Domingos formations, and the identification of a new species for the Lower Devonian Paraná Basin, just as for Lower and Middle Devonian Icla, Belén, Gamoneda and Huamampampa formations, Bolivia.…”