Abstract
AbstractWe describe a new assemblage of small carbonaceous fossils (SCFs) from diagenetically minimally altered clays and siltstones of Terreneuvian age from the Lontova and Voosi formations of Estonia, Lithuania and Russia. This is the first detailed account of an SCF assemblage from the Terreneuvian and includes a number of previously undocumented Cambrian organisms. Recognizably bilaterian‐derived SCFs include abundant protoconodonts (total‐group Chaetognatha), and distinctive cuticular spines of scalidophoran worms. Alongside these metazoan remains are a range of protistan‐grade fossils, including Retiranus balticus gen. et sp. nov., a distinctive funnel‐shaped or sheet‐like problematicum characterized by terminal or marginal vesicles, and Lontohystrichosphaera grandis gen. et sp. nov., a large (100–550 μm) ornamented vesicular microfossil. Together these data offer a fundamentally enriched view of Terreneuvian life in the epicratonic seas of Baltica, from an episode where records of non‐biomineralized life are currently sparse. Even so, the recovered assemblages contain a lower diversity of metazoans than SCF biotas from younger (Stage 4) Baltic successions that represent broadly equivalent environments, echoing the diversification signal recorded in the coeval shelly and trace‐fossil records. Close comparison to the biostratigraphical signal from Fortunian small shelly fossils supports a late Fortunian age for most of the Lontova/Voosi succession, rather than a younger (wholly Stage 2) range.
Highlights
Together these data offer a fundamentally enriched view of Terreneuvian life in the epicratonic seas of Baltica, from an episode where records of non-biomineralized life are currently sparse
The recovered assemblages contain a lower diversity of metazoans than small carbonaceous fossils (SCFs) biotas from younger (Stage 4) Baltic successions that represent broadly equivalent environments, echoing the diversification signal recorded in the coeval shelly and trace-fossil records
For surface sections samples were selected at 1 m intervals, with denser sampling in finergrained lithologies
Summary
Together these data offer a fundamentally enriched view of Terreneuvian life in the epicratonic seas of Baltica, from an episode where records of non-biomineralized life are currently sparse. The recovered assemblages contain a lower diversity of metazoans than SCF biotas from younger (Stage 4) Baltic successions that represent broadly equivalent environments, echoing the diversification signal recorded in the coeval shelly and trace-fossil records. A pronounced increase in the origination rate of small shelly fossil (SSF) taxa occurs at or near the beginning of Stage 2 (Bengtson et al 1990; Maloof et al 2010; Kouchinsky et al 2012). Current records of SSFs, ichnofossils and acritarchs from the Fortunian point to relatively lowdiversity ecosystems compared to Stage 2, or younger counterparts. Phosphatic SSF assemblages from this earliest Cambrian interval are dominated by enigmatic tubular forms (e.g. Anabarites, Hyolithellus, Hexaconularia) and protoconodonts (Protohertzina), typically referred to the Anabarites trisulcatus–Protohertzina anabarica Zone (Hamdi et al 1989; Steiner et al 2004a; Kouchinsky et al 2012). Of sites bearing phosphatized algae and metazoan larvae in South China (Steiner et al 2004b; Liu et al 2017), there is remarkably little accounting of the non-biomineralizing clades that dominate the diversity of most ecosystems
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