Cochleatina: an enigmatic Ediacaran–Cambrian survivor among small carbonaceous fossils (SCFs)

Abstract

Conspicuously few body‐fossil taxa are known to span the Ediacaran–Cambrian boundary, a pattern usually taken to signal either a terminal Proterozoic mass extinction, or taphonomic failure. We draw attention to the emerging record of small carbonaceous fossils (SCFs), which exhibit continuous preservation spanning this critical interval. Here we focus on the enigmatic SCF Cochleatina, a morphologically complex coil‐shaped problematicum that ranges across the Ediacaran–Cambrian divide, and is potentially among the oldest fossil occurrences of metazoans. We report new material of Cochleatina canilovica from the Ediacaran of Estonia and Ukraine, which offers new characters for assessing its palaeobiology. Significantly, new specimens include sets of three‐alike triplets of Cochleatina adhering to organic sheets, suggesting a clustering habit, or grouping of elements within an individual during life; an important step in constraining the morphology and ecology of this Ediacaran–Cambrian problematicum. We present revised systematic descriptions for Cochleatina and C. canilovica, and critically evaluate previous biological interpretations, drawing comparisons with metazoan, algal and protistan analogues. We reject hypotheses supporting Cochleatina as a metazoan mouthpart, and suggest new grounds for viewing Cochleatina as a potential multicomponent predator that trapped protists among microbial mats. Most occurrences are from Baltica, but we synthesize sporadic reports of Cochleatina from other palaeocontinents, pointing to its global distribution during the latest ˜10 myr of the Ediacaran and majority of the earliest Cambrian Fortunian Stage. As a rare example of an ‘Ediacaran survivor’, Cochleatina highlights the broader significance of SCFs as a novel means of tracking evolutionary patterns through the Proterozoic–Phanerozoic transition.

Late Ediacaran occurrences of the organic-walled microfossilsGranomarginataand flask-shapedLagoenaforma collarisgen. et sp. nov.

“…processes and envelopes) provide a useful biostratigraphic tool, and the envelope-bearing Granomarginata is one of the few non-leiosphaerid acritarchs present in low-diversity microfossil assemblages of upper Ediacaran strata, in addition to organically preserved problematica (cf. Golubkova & Raevskaya, 2005;Leonov & Ragozina, 2007;Moczydłowska et al 2015;Slater et al 2020). Microfossils of this material differ from more ubiquitous Proterozoic envelope-bearing taxa such as Simia (also present in the Nama Group) in their fluffy, granular envelope with an uneven outline, which is likely a result of its less resistant nature compared with the central body (Naumova, 1960;Moczydłowska, 1991).…”

Late Ediacaran organic microfossils from Finland

“…Detrital zircon U-Pb ages have subsequently constrained the Visingsö Formation to a maximum depositional age of ≤886 ± 9 Ma (Moczydłowska et al 2017), and recent microfossil studies also suggest this formation was deposited during the Tonian (Loron & Moczydłowska, 2018). Klein et al (2015), however, point out that many of the form-taxa reported from the Hailuoto Formation by Tynni & Donner (1980) are actually found in much younger sediments elsewhere in the Baltic region and East European Platform, for example, in late Ediacaran strata from the Kotlin Formation of Estonia (Mens & Pirrus, 1997;Meidla, 2017;Arvestål & Willman, 2020;Slater et al 2020). A particularly close comparison can also be drawn with OWM assemblages from the late Ediacaran Redkino and Kotlin regional stages of the Lyamtsa, Verkhovka, Zimnie Gory and Yorga formations of the White Sea region in Russia (e.g.…”

“…The majority of samples produced abundant entangled mats of Siphonophycus, Palaeolyngbya and Rugosoopsis exhibiting a mesh-like growth habit (Figs 6,7), where filaments are densely interwoven 7a). Frequently the density of overlapping filaments is such that they form a sheet-like layer that has been compressed into a single carbonaceous film (see Martí Mus, 2014;Slater et al 2020). Some of these mats are of mixed composition (e.g.…”

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“…The lower one consists of coarser-grained beds with predominantly grey sandstones, while the upper member comprises predominantly greengrey and red, fine-grained beds of argillites and aleurolites. Remains of algae are represented by different species of Vendotaenidae (Gnilovskaya et al 1988) are common in the Kanylivka Series; in the Krushanivka Formation, remains of Cochleatina canilovica (small carbonaceous fossil) rarely occur and were redescribed recently (Slater et al 2020). Due to shallow-water depositional conditions, small wave ripples are very common, whereas animal remains are almost entirely absent except ichnofossils and fossil algae (Gureev, 1985(Gureev, , 1988Fedonkin, 1987).…”

“…The Kryvchany Member is represented in the lower part by fine-to medium-grained sandstones (up to 3-4 m in thickness) and in the upper part by thick beds of alternating green and grey sandstones, aleurolites, and argillites with a total thickness of ca. 30 m. There were found enigmatic fossil Cochleatina canilovica Aseeva, 1974(Slater et al 2020. The Durniakivtsy Member is made of alternation of brown aleurolites, argillites, and grey sandstones, rarely with lenses of limestones and phosphoritic argillites, with a total thickness of ca.…”