Linguliform brachiopods across a Cambrian–Ordovician (Furongian, Early Ordovician) biomere boundary: the Sunwaptan–Skullrockian North American Stage boundary in the Wilberns and Tanyard formations of central Texas

Abstract

The Cambrian-Ordovician Diversity Plateau, between the Cambrian Explosion and the Ordovician Radiation, is punctuated by a series of well-documented Laurentian trilobite extinction events. These events define the bounding surfaces of trilobite ‘biomeres’ that correspond to North American stages, including those of the Sunwaptan and Skullrockian. Trilobites show a consistent pattern of recovery across these boundaries, and commonly each extinction and replacement of taxa is interpreted as a single event as changing environmental conditions spurred shoreward migration of shelf or oceanic faunas that displaced established cratonic faunas. Linguliform brachiopods are also abundant in strata of this interval, and we investigate their stratigraphic distribution across the Sunwaptan–Skullrockian Stage boundary in Texas through high-resolution stratigraphic sampling of subtidal sediments. We document complete genus- and species-level turnover of the linguliform brachiopod fauna coincident with trilobite extinction events, suggesting that these brachiopods were affected by the same factors that affected trilobites. The Skullrockian replacement fauna was cosmopolitan, with ties to Gondwana and Kazakhstan and to the Laurentian shelf environment. The timing of appearances of taxa suggests that the faunal migration onto the Laurentian shelf came from elsewhere during a transgression. The disappearance of the Sunwaptan fauna and the arrival of the Skullrockian fauna are distinct events. We suggest that ‘biomere’ events may be complex, and the cause of the extinction is not necessarily the same event that facilitates the appearance of a replacement fauna. We describe one new species,Schizambon langei.UUID:http://zoobank.org/f6a5c11f-cd3d-4c16-b184-d808d3a5285f

Lower Tremadocian (Ordovician) lingulate brachiopods from the Central Andean Basin (NW Argentina) and their biogeographical links

“…Especially relevant is the presence of the obolids Leptembolon and Libecoviella, which constitute, together with some other taxa, the Thysanotos-Leptembolon Association recorded , 2007, Popov et al 2013 andPopov 2021. Complementary bibliographic sources: Bohemia (Havlíček 1982(Havlíček , 1989Mergl 1995Mergl , 2002Mergl , 2018; Laurentia (Popov et al 2002, Holmer et al 2005, Freeman et al 2018; Avalonia (Sutton et al 1999(Sutton et al , 2000Cocks & Popov 2019); Baltica (Popov & Holmer 1994, 1995; Alborz (Iran: Popov et al 2008, Ghobadi Pour et al 2011; NW Argentina (Benedetto & Muñoz 2015; South Urals (Popov & Holmer 1994, 1995; Australia (Percival & Engelbretsen 2007); Malyi Karatau (Kyrgyzstan: Popov & Holmer 1994, 1995Holmer et al 2001); S Kendyktas Range (Kazakhstan: Popov & Holmer, 1994)…”

The siphonotretide brachiopod Schizambon from the Early Ordovician of South China: ontogeny and affinity

“…Schizambon sp. Freeman et al ., 2018, upper part of San Saba Member of the Wilberns Formation and lowest part of Threadgill Member of the Tanyard Formation (Cambrian Furongian – Ordovician Tremadocian Cordylodus lindstromi s.l ., Iapetognathus and Cordylodus angulatus conodont zones and the Symphysurina trilobite Zone).…”

“…Schizambon convexus González‐Gómez, 2005, Val d’Homs Formation (Cambrian, Guzhabngian), Montagne Noire, southern France. Schizambon langei Freeman et al ., 2018, Threadgill Member of the Tanyard Formation (Lower Ordovician, Cordylodus angulatus conodont Zone and the Loxodus bransoni Subzone of the Rossodus manitouensis conodont Zone), Texas, USA. Schizambon obtusus Holmer et al ., 2005, from Barn Canyon Member, House Limestone Formation (Ordovician Tremadocian, Cordylodus angulatus conodont Zone), Utah, USA.…”

“…2015; Freeman et al . 2018). There is no previous record of Schizambon in South China, therefore the occurrence of Schizambon tongziensis in the Tungtzu Formation (lower Tremadocian, Rossodus manitouensis – Chosonodina herfurthi Zone) is of considerable interest.…”

Oceanic redox conditions during the terminal Cambrian extinction event

“…Like other end-of-biomere extinctions, it was first recognized on the Laurentian shelf where trilobites experienced major and rapid turnover (Stitt, 1971;Palmer, 1984). This extinction was subsequently shown to also affect conodonts and brachiopods simultaneously (Miller et al, 2006;Freeman et al, 2018).…”