Morphological variation in the rangeomorph organism Fractofusus misrai from the Ediacaran of Newfoundland, Canada

Abstract

The Ediacaran rangeomorph Fractofusus misrai is the most common and best-preserved of the E Surface fossil assemblage in the Mistaken Point Ecological Reserve of southeastern Newfoundland, Canada. Fractofusus has been interpreted as a fusiform epifaunal soft-sediment recliner, and like other rangeomorphs it has a self-similar, fractal-like branching morphology. The rangeomorph branching of Fractofusus has been considered to be identical on the upper and lower surfaces; however, study of specimens with complex biostratinomic histories suggests clear differences between the upper and lower surfaces. The first-order branches grew downwards into the sediment from a high point near the midline but grew above the sediment–water interface at their lateral and distal margins. Our new three-dimensional appreciation of rangeomorph branching in Fractofusus explains many of the taphomorphs of Fractofusus including straight, curved, kinked and tousled forms. The three-dimensional morphology, mode of life, taphonomy and palaeoenvironmental interactions of F. misrai are discussed along with a new three-dimensional reconstruction.

Frond orientations with independent current indicators demonstrate the reclining rheotropic mode of life of several Ediacaran rangeomorph taxa

“…It is possible that the west side had been flipped via mechanical damage and folded onto the opposite side, but could equally be due to growth. This “twisting” differs from nonidiomorphic “kinked” Fractofusus specimens that were bent and repositioned with the original side still facing down (Taylor et al 2022).…”

“…However, this position would also reduce current-related damage by confining current eddying to the distal end of the organisms. These trade-offs and orientations are suggestive of a reclining position in life (Seilacher 1992; Gehling and Narbonne 2007; Taylor et al 2022). The two orientation groups show very small differences in morphometric traits, as shown in Tables 2 and 3 and the PCPs (Figs.…”

Hydrodynamic insights into the paleobiology of the Ediacaran rangeomorph Fractofusus misrai

“… 33 However, Fractofusus has always been interpreted as a reclining organism lying flat on the seafloor 24 , 40 supported by their apparently random orientation at Bristy Cove, the E Surface at Mistaken Point Ecological Reserve (MPER), and the Johnson/H14 surface at Discovery Global Geopark 21 , 30 , 39 , 40 , 41 and also the ubiquitously well-preserved nature of their lower surface impressions. 18 , 31 Preferential orientations of Fractofusus misrai , oblique to a paleocurrent, have however been reported at Capelin Gulch near Melrose in the Catalina Dome ( Figure 1 ). 22 This fossiliferous surface is significant because paleocurrents at the site can be determined from current ripples associated with the fossiliferous bedding plane.…”

“…Species of the rangeomorph genus Fractofusus ( F. misrai and F. andersoni ) are endemic to the offshore to deep basinal Ediacaran facies of the island of Newfoundland 3 , 16 , 17 , 18 (and putative examples from McKenzie Mountains Canada) 19 where they are found on minor hiatal surfaces in turbiditic successions associated with well-developed matgrounds. 17 Fractofusus misrai dominates the D and E surfaces at Mistaken Point 20 , 21 and the “Melrose Surface” at Capelin Gulch in the Discovery UNESCO Global Geopark.…”

“… 45 In this study, we present a novel hydrodynamic approach to studying F. misrai , integrating the detailed three-dimensional geometry published by Taylor et al. 18 ( Figure 3 ) and the statistically significant orientation groups found by Pérez-Pinedo et al. 22 We aim to document the fluid flow near the reconstructed F. misrai relevant to feeding strategies and metabolite collection (cf.…”