A new reconstruction of Protolyellia (Early Cambrian psammocoral)

Abstract

A new reconstruction of Protolyellia (psammocoral) from the Mickwitzia sandstone, Early Cambrian of south-central Sweden, is proposed. Observations, conceptual analysis and physical modelling indicate that the distinctive honeycomb or (less frequently) ridge sculpture of the upper side of the sand-button was a wrinkle pattern in a flexible epithelium. Wrinkling was caused by contraction of a subepithelial muscle layer joined to the epithelium by connective tissue. Fine-grained sand particles adhering on, or embedded within, the epithelium preserved its surface relief after the soft parts decomposed. The sand-bearing epithelium covered a subcylindrical structure attached around the periphery of the sand-button and extending upwards. This structure is occasionally preserved felled horizontally near a sand-button, but is more commonly found as isolated shreds. Sudden burial caused the lower portion of this structure to contract and wrinkle against the tissues containing the sand-button. After the soft parts decomposed, sediment compaction pasted the wrinkled layer onto the sand-button, thus producing the typical preservation mode. The wrinkle pattern of Protolyellia differs from those of Recent cnidarians, and suggests that Protolyellia did not possess mesenteries. Protolyellia may be more distantly related to modern cnidarians than previously assumed. In addition, alternative affinities with Ediacaran frond-bearing forms cannot be excluded.

Patterns of Evolution of the Ediacaran Soft-Bodied Biota

“…In addition, Brachina delicata and Solza margarita should also be evaluated as possible taphomorphs of Kimberella quadrata (Trusler et al, 2007). The term ''Psammocorallia'' refers to benthic organisms in which the lower (aboral) part of the sacciform body is preserved as three-dimensional hemispherical sandstone casts (Seilacher, 1992;Seilacher and Goldring, 1996;Savazzi, 2007Savazzi, , 2012, although it has not been fully resolved how these structures formed (e.g., Jensen, 1997) (Fig. 1.2).…”

Problematic megafossils in Cambrian palaeosols of South Australia

“…2000, fig. 88), burrow backfill (Retallack 2001 b ) or internal chambering or backfill of a sediment‐ingesting organism (Seilacher 1992; Savazzi 2007), because it cannot have been moved within the whole structure, as revealed by the following observations. In one vertical face, two Erytholus were exposed by breaking open the rock vertically and recording former orientation (Text‐fig.…”

Internal structure of Cambrian vendobionts Arumberia, Hallidaya, and Noffkarkys preserved by clay in Montana, USA

“…By an alternative interpretation (Kumar & Pandey, 2008;Kolesnikov et al, 2012;McMahon et al, 2021), Arumberia is a continuous surface microbial texture and not a discrete individual fossil, but that interpretation does not apply to its holotype specimens (Retallack & Broz, 2020) or the material described here. The silt or sand associated with Arumberia is similar to equally problematic "psammocorals" (Seilacher, 1992), but these have much higher relief and an outer organic rind enclosing passive sand fill (Savazzi, 2007), not matched by the internal orthogonal organic seams of Arumberia at Fishtrap Lake (Figs 6C-D, K) and in Central Australia (Retallack & Broz, 2020, figs 6c, 8b, d, f).…”