Ediacaran Fronds from South Australia and Newfoundland

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Grimes, Kelsey
Ediacaran , Paleontology , Geology , Fronds
The Ediacara biota (575-539 Ma) represents a seminal event in the evolution of life, the first abundant appearance of large, architecturally complex, soft-bodied organisms after three billion years of mostly microbial evolution. Fronds occupied all tiers of the Ediacaran ecosystem and were the first animals with a construction allowing them to partition the water column macroscopically resulting in a tiering ecosystem similar to Phanerozoic marine ecosystems in structure. Elongate fronds were a rarity in the Ediacaran, one in particular, formally named Rangea longa, was defined in 1966 but has not been studied in detail since. The specimens of this elongate frond are disparate in appearance, which have resulted in their exclusion from global syntheses and assigned to five different genera since its formal designation. The specimens of the Mincham-Flounders collection constitute one species with four taphonomic variants that illustrate the 3D structure of this frond. Akrophyllas longa is an elongate rangeomorph bifoliate frond attached to a bulbous holdfast either directly or with a short stem. The primary branches consistently appear sigmoidal in shape with rectangular secondary branches oriented perpendicular to the primaries. These fronds can be assigned to the Rangeomorpha, an extinct clade near the base of animal evolution, but exhibit an architecture and a construction that differs significantly from all other rangeomorph genera yet described and are herein formally designated as a new genus. Frond dusters, small fronds never reaching more than 8 cm in height as adults, occur commonly in the Ediacaran of Avalonian Newfoundland but have not been extensively described. A new frond duster is described and named here that displays unique architecture, otherwise unknown from the Ediacaran biota and easily distinguished from all Ediacaran macrofossils, justifying its erection as a new genus and species. This frond is a spatulate, feather-like frond with primary branches emerging from a single point at the base of the petalodium, complete with a bulbous holdfast with filamentous connections. Convergent evolution has resulted in numerous frond dusters sharing a similar body plan. We are slowly uncovering the diversity of fronds occupying the lowest tier of the Ediacaran ecosystem.
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