Fossils from the deep-sea Ediacaran biotas of Newfoundland are among the oldest architecturally complex soft-bodied macroorganisms on Earth. Most organisms in the Mistaken Point-type biotas of Avalonia — particularly the fractal-branching frondose Rangeomorpha — have been traditionally interpreted as living erect within the water column during life. However, due to the scarcity of documented physical sedimentological proxies associated with fossiliferous beds, Ediacaran paleocurrents have been inferred in some instances from the preferential orientation of fronds. This calls into question the relationship between frond orientation and paleocurrents. In this study, we present an integrated approach from a newly described fossiliferous surface (the “Melrose Surface” in the Fermeuse Formation at Melrose, on the southern portion of the Catalina Dome in the Discovery UNESCO Global Geopark) combining: (1) physical sedimentological evidence for paleocurrent direction in the form of climbing ripple cross lamination, and (2) a series of statistical analyses based on modified polythetic and monothetic clustering techniques reflecting the circular nature of the recorded orientation of Fractofusus misrai specimens. This study demonstrates the reclining rheotropic mode of life of the Ediacaran rangeomorph taxon Fractofusus misrai and presents preliminary inferences suggesting a similar mode of life for Bradgatia sp. and Pectinifrons abyssalis based on qualitative evidence. These results advocate for the consideration of an alternative conceptual hypothesis for the position of life of Ediacaran organisms in which they are interpreted as having lived reclined on the seafloor, in the position that they are preserved.

The data presented in this study were collected from a single fossiliferous surface of the Fermeuse Formation that crops out on the southeastern margin of the Catalina Dome, Bonavista Peninsula (see O’Brien and King 2005) (Fig. 2). A 0.1-0.6 mm thick ripple cross-laminated sandstone bed indicates a paleocurrent orientation of 102º SE. Data collection was grid-based, with 41 squares of approximately 1.5 x 1.5 m completely documented with respect to their paleontology. Grids were photographed and orientation data collected (n_t = 208 specimens of five different taxa were measured: Fractofusus n_f = 190, Pectinifrons n_p = 12, Bradgatia n_b = four, Primocandelabrum n_pr = one, and Charniodiscus n_c = one). Fragmental specimens of all studied taxa were excluded from the analysis due to analytical difficulties and potential to introduce sampling bias. Only Fractofusus was included in the statistical analysis due to the low numbers of well-preserved specimens of all other taxa. 

Morphometric traits were retrieved from field photography and analysed with the software ImageJ (Schneider et al. 2012). The data were analysed by the Gaussian finite mixture model-based clustering algorithms of the package mclust (Scrucca et al. 2016). The circular variable was tested to identify potential departures from uniformity using the packages circular (Agostinelli and Lund 2017) and CircMLE (Fitak and Johnsen 2017). Modified monothetic and polythetic cluster analysis were conducted aided by the monoClust package in R (Tran et al. 2021). 

Microsoft Excel; R.