Australia: The Land Where Time Began

A biography of the Australian continent 

Aspidella, Form genus from the Ediacaran – Morphology and Taphonomy

Aspidella is a common disc-like form genus that is a member of the Ediacara Biota with global distribution. It is present prolifically, n>1,000, in locally dense assemblages on the bases of sandstone beds in the eponymous Ediacara Member of the Rawnsley Quartz, South Australia. Aspidella has been interpreted as a holdfast of a frondose organism that was Charniodiscus-like, because of its association with stalks, fronds, and textured organic surfaces (TOS), which in life had its holdfast secured within or beneath a sandy microbial mat with its stalk and frond protruding into the water column above the substrate. Aspidella exemplifies faunal heterogeneity of bed-scale that was characteristic of Ediacara fossil assemblages, being the dominant component of 4 fossiliferous beds and a minor component of many others. Moreover, Aspidella is characterised by strong morphological variability, which included the presence or absence of particular distinct features, including preservation that was variable as external or internal moulds, relief that was variable and a broad range of sizes. The distribution of morphological characters is, however, not related to the size of Aspidella or the composition of its bed assemblage. In this paper Tarhan et al. suggest that this morphological diversity is not an expression of ontogenetic or anatomical differences at species level, rather it is the product of differential taphonomy that is related to substrate sedimentology and biogenic factors, in particular the presence or absence of TOS which is composed of Funisia, a eukaryotic tubular organism.

Sources & Further reading

1. Tarhan, L. G., M. L. Droser, J. G. Gehling and M. P. Dzaugis (2015). "Taphonomy and morphology of the Ediacara form genus Aspidella." Precambrian Research 257(0): 124-136.