Problematic megafossils in Cambrian palaeosols of South Australia

Abstract

Other axial structures (Prasinema nodosum and P. adunatum gen. et spp. nov.) are larger and show distinctive surface irregularities (short protuberances and irregular striations, respectively). The size and form of these filaments are most like rhizines of soil-crust lichens. Other evidence of life on land includes quilted spheroids (Erytholus globosus gen. et sp. nov.) and thallose impressions (Farghera sp. indet.), which may have been slime moulds and lichens, respectively. These distinctive fossils in Cambrian palaeosols represent communities comparable with modern biological soil crusts.

Reply to comments on Retallack 2011: Problematic megafossils in Cambrian Palaeosols of South Australia

“…Fifth, they allow that the Cambrian Lake Frome Group includes palaeosols (Retallack 2008), as also proposed by Stock (1974) and Moore (1990). Sixth, they highlight comparisons between Ediacaran and the Cambrian fossils and palaeosols, one of the aims of Retallack (2011). Seventh, they allow me to affirm the orientations of the fossils which were either crack‐out specimens from outcrop, or slabs and thin sections oriented (and illustrated) vertical to bedding (Retallack 2008, 2011).…”

“…Third, two authorities on trilobites (Jago and Paterson), after close inspection of the type material, find no similarity between Erytholus and enrolled trilobites, a conclusion shared by Retallack (2011). Fourth, an expert on Ediacaran fossils (Gehling) finds little similarity between Erytholus and Ernietta or Pambikalbae , another conclusion of Retallack (2011). Fifth, they allow that the Cambrian Lake Frome Group includes palaeosols (Retallack 2008), as also proposed by Stock (1974) and Moore (1990).…”

“…Second, they have prepared colour illustrations of these green and red fossils to supplement the original black and white versions (although only a tiny corner of the originally arrowed fossil is seen in their panel C, which is centred on an unnamed mottle). Third, two authorities on trilobites (Jago and Paterson), after close inspection of the type material, find no similarity between Erytholus and enrolled trilobites, a conclusion shared by Retallack (2011). Fourth, an expert on Ediacaran fossils (Gehling) finds little similarity between Erytholus and Ernietta or Pambikalbae , another conclusion of Retallack (2011).…”

“…J ago et al . (2012) regard problematic fossils described by Retallack (2011) as dubiofossils or pseudofossils from modern weathering, yet fail to propose a specific plausible model for formation of the disputed fossils in a weathering profile. Nevertheless, their comments are helpful for many reasons.…”

“…The main claim of Jago et al . (2012) is that fossils named by Retallack (2011) lack regularity of form as a criterion of biogenicity. A more comprehensive list of criteria for assessing biogenicity of Precambrian problematica (from Hoffman 2004) is as follows: (1) known provenance, (2) plausible environment for life, (3) same age as the rock, (4) plausible composition, (5) taphonomic series, (6) repeated complexity.…”