Elongate Ediacaran fronds from the Flinders Ranges, South Australia

Abstract

Decimeter-scale, elongate, fossil fronds from the Ediacara Range in South Australia were formally described as Rangea longa Glaessner and Wade, 1966, but the disparate nature of documented specimens has hindered their inclusion in global syntheses and has resulted in these fossils being assigned to at least five different genera in two different clades since their discovery. Detailed study of the type material from the Ediacara Range and the few specimens subsequently collected elsewhere in the Flinders Ranges reaffirms that these specimens represent a single species, with the apparent morphological variation between specimens entirely taphonomic and reflecting the obverse and reverse surfaces of these fronds coupled with the orientation of the frond axis and petaloids at different angles relative to the sea bottom on which they were preserved. The preserved architecture of these fronds constitutes three orders of branching microstructure that are strictly orthogonal to immediately higher and lower orders. This implies affinities with the arboreomorphs, but representing a new frond genus herein named Akrophyllas. Akrophyllas n. gen. differs from all other Ediacaran fronds in exhibiting a stalk that is visible only on one side of the frond and is internal to the other side where the first-order branches instead meet at a zigzag axial trace. Akrophyllas n. gen. was attached to a bulbous holdfast on the sea bottom, and evidence for current scours that formed in the lee of the fronds and for a strong current alignment of felled fronds with depositional overlap of adjacent fronds imply an upright, epibenthic lifestyle for Akrophyllas longa new combination. UUID: http://zoobank.org/86e26477-7b1e-45da-870c-1b5d28fc510c