Abstract
AbstractConspicuously 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.
Highlights
T H E Ediacaran–Cambrian boundary, approximately 541– 539 Ma (Linnemann et al 2019), is widely recognized as a juncture of exceptional ecological and evolutionary importance (Conway Morris 2000; Butterfield 2007; Budd & Jensen 2017)
The apparent disconnect in the body fossil record is contrasted by the relatively unbiased trace fossil record, which instead documents a signal of continuity between late Ediacaran and earliest Cambrian benthic bilaterian behaviour (e.g. Jensen 2003; Mangano & Buatois 2017; Kesidis et al 2019)
We focus on an enigmatic small carbonaceous fossils (SCFs) taxon, Cochleatina, a distinctive and widely distributed taxon that appears to span the Ediacaran–Cambrian divide
Summary
Drillcore, 180 m depth in Maidla F-238 drillcore, 153 m in the Toila 77 drillcore, and 119.4 m from the Meriku€la F-169 drillcore, whilst those from the drillcore No 700 in Podillya, Ukraine were sourced from a productive layer at 184 m depth. The new specimens from Estonia and Ukraine are assigned to C. canilovica on the basis of their consistent spinose serration, ribbon oriented perpendicular to the bobbin axis, and four broad ribbon zones, features which are lacking in other taxa (see Systematic Palaeontology, below). Both the Estonian and Ukrainian assemblages are consistent with the currently known range of C. canilovica which is reported from the Kotlin regional stage of the late Ediacaran, and the lowermost part of the Rovno regional Ediacaran/Cambrian stage. Either these clusters represent groups of three similar individuals from a population with a benthic ecology, or were clustered prior to sinking from suspension, or are the recalcitrant components of a single organism that has otherwise decayed away
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