Small shelly fossils and carbon isotopes from the early Cambrian (Stages 3–4) Mural Formation of western Laurentia

Abstract

The extraordinary window of phosphatized and phosphatic small shelly fossils (SSF) during the early and middle Cambrian is an important testament to the radiation of biomineralizing metazoans. While SSF are well known from most Cambrian palaeocontinents during this time interval, western Laurentia has relatively few SSF faunas.Here we describe a diverse SSF fauna from the early Cambrian (Stages 3-4) Mural Formation at three localities in Alberta and British Columbia, Canada, complemented by carbon isotope measurements to aid in a potential future bio-chemostratigraphic framework. The fauna expands the recorded SSF assemblage diversity in western Laurentia and includes several brachiopods, four bradoriids, three chancelloriids, two hyoliths, a tommotiid and a helcionellid mollusc as well as echinoderm ossicles and specimens of Microdictyon, Volborthella and Hyolithellus. New taxa include the tommotiid genus Canadiella gen. nov., the new bradoriid species Hipponicharion perforata sp. nov. and Pseudobeyrichona taurata sp. nov. Compared with contemporaneous faunas from western Laurentia, the fauna is relatively diverse, particularly in taxa with originally phosphatic shells, which appear to be associated with archaeocyathid build-ups. This suggests that the generally low faunal diversity in western Laurentia may be at least partly a consequence of poor sampling of suitable archaeocyathan reef environments. In addition, the tommotiid Canadiella filigrana appears to be of biostratigraphical significance in Cambrian Stage 3 strata of western Laurentia, and the unexpected high diversity of bradoriid arthropods in the fauna also suggests that this group may prove useful for biostratigraphical resolution in the region.

First Report of Small Shelly Fossils from the Cambrian Miaolingian Limestones (Zhangxia and Hsuzhuang Formations) in Yiyang County, Henan Province of North China

“…Specimens of Hyolithellus have been found in life position from lower Cambrian dolostone and are regarded as the possible stem group of annelids [80]. However, it is hard to identify species of Hyolithellus only based on the morphology of an individual [80,81]. The new record of Hyolithellus sp.…”

“…Remark. The samples are actually preserved as secondary phosphatic infill of the cavities of echinoderm stereom structure (Figure 3E1,E2) [81]. It is hard to perform any taxonomic work based on the echinoderm ossicles.…”

Brachiopods from the Latham Shale Lagerstätte (Cambrian Series 2, Stage 4) and Cadiz Formation (Miaolingian, Wuliuan), California

“…Mickwitzia occidens occurs both in the Indian Springs Lagerstätte (the Poleta Formation) in Nevada, and in the Latham Shale in California, which is of Nevadella Biozone to Bonnia-Olenellus Zone in age (English and Babcock, 2010; Butler et al, 2015). Mickwitzia muralensis occurs in the Mural Formation belonging to the Nevadella Zone with the boundary to the overlying Bonnia-Olenellus Zone (Balthasar, 2004; Skovsted et al, 2021). Thus, these occurrences support tentative correlation of the Nevadella to Bonnia-Olenellus zones in Laurentia with the Dailyatia odyssei Zone in South Australia.…”

Lower Cambrian (Series 2) small shelly fossils from along Nares Strait (Nunavut and Greenland; Laurentia)

“…Specimens collectively assigned to Beyrichona are similar in shape to material from the basal limestone of the Mural Formation of western Canada described by Skovsted et al (2020), whereas Beyrichona avannga from the Kap Troedsson Formation of central North Greenland has proportionately taller shields (Peel 2017). Small specimens are amplete (Fig.…”

“…The fauna from North-East Greenland (Skovsted 2006) contains virtually all of the recorded taxa, notable exceptions include Kordesphecia and Pojetaia robsonae n. sp. Helcionelloid molluscs, Hyolithellus, Chancelloria and echinoderm plates are present in all three assemblages from around Nares Strait, but various species of these are common in most described Laurentian faunas of early Cambrian age (Landing and Bartowski 1996;Nowlan 2001;Landing et al 2002;Skovsted 2006: Skovsted and Peel 2007Wotte and Sundberg 2017;Devaere et al 2019;Skovsted et al 2020). The hyolith Cupitheca (Actinotheca of Nowlan 2001) is also a shared taxon of common occurrence (Figs.…”