A Gondwanan perspective on the Ordovician Radiation constrains its temporal duration and suggests first wave of speciation, fuelled by Cambrian clades

Abstract

This study presents a Cambrian–Ordovician (Cambrian, ‘Series 3’ – Katian, Ka4) brachiopod α‐diversity curve for the Iberian terrane. Three diversity pulses characterized the northern Gondwanan margin through the studied interval; an initial increase in linguliformean diversity that culminated during the Tremadocian (Tr3); a second, Darriwilian (Dw2) pulse caused primarily by a rise in orthid species; and a third pulse during Katian times (Ka3–4) marking the most diverse and phylogenetically complex faunas recorded in this study. Each of the three diversity pulses is phylogenetically distinct and characterized by large turnover rates. The first pulse consists almost exclusively of remnants of the Cambrian Evolutionary Fauna, whereas the second pulse shows a sudden rise of clades typical of the Paleozoic Evolutionary Fauna. The fact that otherwise typical Cambrian clades also radiated at the dawn of the Ordovician suggests that whatever facilitated the emerging Ordovician Radiation, also benefitted these ancient lineages. However, eventually the succeeding Paleozoic Evolutionary Fauna came to dominate during the second diversity pulse. This pulse represents a high‐latitude correlative to the main pulse of the Ordovician Radiation. Although it coincides with a globally occurring transgression of eustatic nature, our analysis shows that the generic composition remained overwhelmingly endemic up through the Darriwilian–Sandbian interval. Opposed to this, the third pulse coincides with the globally occurring Boda warming event, which also marks a time of global dispersal. In Iberia, this is reflected by almost entirely cosmopolitan brachiopod faunas, suggesting that the phases of rapid speciation which characterize the Ordovician Radiation had ceased by the mid‐Katian.

Ordovician ironstone of the Iberian margin: Coastal upwelling, ocean anoxia and Palaeozoic biodiversity

“…Research reported herein focuses on the upper Los Cabos Group and Luarca Formation in the Leonese Mountains and the Armorican Quartzite, Castillejo Formation, and Fombuena Formation in the Eastern Iberian Chain (Figures 2 and 4). Collectively, these units record accumulation from the Floian to middle Katian (ca 478-449 Ma; Figure 4; Pérez Estaún et al, 1990;Gutiérrez-Marco et al, 1999;Cole et al, 2017;Colmenar and Rasmussen, 2017). Detrital zircon provenance analysis suggests sediment was derived from both the West African and Saharan cratons, placing the Iberian shelf near northern Africa (Figure 3;Díez Fernández et al, 2010;Pastor-Galán et al, 2013;Shaw et al, 2014).…”

“…Ironstone occurs in the Herrera Unit of Álvaro et al (2018b). Pale red colour in stratigraphic column highlights approximate depositional age of ironstone (Gutiérrez-Marco et al, 1999;Cole et al, 2017;Colmenar and Rasmussen, 2017). The base of ironstone in the Peña del Tormo and Marité members is locally erosive.…”

“…The younger upper sequence occurs in the middle Luarca Formation and correlative Fe-rich sedimentary rocks of the Eastern Iberian Chain. This sequence contains two distinct ironstone horizons of middle Darriwilian (ca 463 Ma) and late Sandbian (ca 454 Ma) age that are important stratigraphic markers throughout the region (Figure 9; Gutiérrez-Marco et al, 1999;Bergström et al, 2009;Cole et al, 2017;Colmenar and Rasmussen, 2017). In the Eastern Iberian Chain, haematitic granular ironstone forming these horizons caps proximal parasequences (Facies 2; Figure 9), whereas in the Luarca Formation laminated ironstone composed of Fe and Mg-silicates characterizes the base of distal parasequences (Facies 7 and 8; Figure 9).…”

The Great Ordovician Biodiversification Event (GOBE): definition, concept and duration

“…The early history and evolution of the phylum have, not surprisingly, a strong influence on the composition and shape of the curve. There are strong peaks reported from along the northern Gondwanan margin, during the Tremadocian, dominated by linguliform brachiopods; at the same time, the diversification of the Cambrian evolutionary fauna continued in shallow‐water siliciclastic facies (Colmenar & Rasmussen ). During the same interval in tropical Gondwana (South China), orthide and syntrophide faunas flourished prior to the massive spike in diversity during the Darriwilian (Zhan & Harper ).…”

Contextualizing the Onset of the Great Ordovician Biodiversification Event

“…Around Gondwana, the onset and development of the GOBE are charted in Ordovician successions of the Iberian Peninsula by Colmenar & Rasmussen (), with an initial increase in the diversity of linguliformean brachiopods that culminated as early as the Tremadocian, followed by pulses of rhynchonelliform diversification in the Darriwilian and Katin. Lefebvre et al .…”