ALBERT

Description: The Ediacaran frond Charnia, known mainly from fragmentary leaf-like fronds from around the world, is represented by completely preserved specimens with holdfasts in the Mistaken Point biota of Newfoundland. Previous reconstructions of Charnia from two-dimensional impressions were significantly oversimplified, resulting in three-dimensional reconstructions which highlighted a sheet-like morphology. Overlapping relationships and internal structures are rarely (if ever) preserved, and only through detailed photography together with both landmark and traditional morphometric analyses of numerous complete Charnia specimens can the preservational biases be removed. Charnia is reinterpreted here as having a series of individual overlapping primary branches attached to an internal central stalk, and with individual branches constrained by an internal, organic skeleton and/or attachments between adjacent branches. Three species, C. masoniFord 1958, C. wardi Narbonne & Gehling 2003, and C. antecedens sp. nov. can be distinguished on the basis of length/width ratios and the degree of attachment of adjacent branches. Morphological, taphonomical, and ecological studies at Mistaken Point imply that Charnia was a sessile, epibenthic frond that fed from suspension in this deep-water volcaniclastic setting. Evolution of more rigorous connections between the primary branches allowed Charnia to migrate into more turbulent, shallower-water habitats by the late Ediacaran.

Description: A bstract Impressions of soft-bodied Ediacaran megafossils are common in deep-water slope deposits of the June beds at Sekwi Brook in the Mackenzie Mountains of NW Canada. Two taphonomic assemblages can be recognized. Soles of turbidite beds contain numerous impressions of simple ( Aspidella ) and tentaculate ( Hiemalora, Eoporpita ) discs. A specimen of the frond Primocandelabrum is attached to an Aspidella -like holdfast, but most holdfast discs lack any impressions of the leafy fronds to which they were attached, reflecting Fermeuse-style preservation of the basal level of the community. Epifaunal fronds ( Beothukis, Charnia, Charniodiscus ) and benthic recliners ( Fractofusus ) were most commonly preserved intrastratally on horizontal parting surfaces within turbidite and contourite beds, reflecting a deep-water example of Nama-style preservation of higher levels in the community. A well-preserved specimen of Namalia significantly extends the known age and environmental range of erniettomorphs into deep-water aphotic settings. Infaunal bilaterian burrows are absent from the June beds despite favorable beds for their preservation. The June beds assemblage is broadly similar in age and environment to deep-water Avalonian assemblages in Newfoundland and England, and like them contains mainly rangeomorph and arboreomorph fossils and apparently lacks dickinsoniomorphs and other clades typical of younger and shallower Ediacaran assemblages. Fossil data presently available imply that the classically deep- and shallow-water taxa of the Ediacara biota had different evolutionary origins and histories, with sessile rangeomorphs and arboreomorphs appearing in deep-water settings approximately 580 million years ago and spreading into shallow-water settings by 555 Ma but dickinsoniomorphs and other iconic clades restricted to shallow-water settings from their first known appearance at 555 Ma until their disappearance prior to the end of the Ediacaran.

Description: 〈span〉The Rangeomorpha are the oldest, most diverse, and most disparate clade of Ediacaran macrofossils. Easily identifiable by their self-similar branching pattern, they occupied epibenthic niche space ranging from the lowest-tiered and recumbent taxa up to metre-long upright fronds. A phylogenetic analysis using the largest and most complete character set known for this group scored for 14 separate taxa was undertaken to resolve their internal relationships and test previous hypotheses of their evolutionary and ecological history. Owing to the lack of consensus on the relationship amongst Ediacaran clades, several permutations with different potential outgroup taxa were performed. Across these analyses, there is a strong signal for an upright frondose ancestral state for this clade, likely displaying primary branches that were double-sided, nonrotated, with the lower-tiered and recumbent forms being derived members of a single subclade. This has implications on the life history reconstruction as well as taxonomic implications for this clade and the origins of large multicellular life in the late Ediacaran.〈/span〉

Description: Rangea is the type genus of the Rangeomorpha, an extinct clade near the base of the evolutionary tree of large, complex organisms which prospered during the late Neoproterozoic. It represents an iconic Ediacaran taxon, but the relatively few specimens previously known significantly hindered an accurate reconstruction. Discovery of more than 100 specimens of Rangea in two gutter casts recovered from Farm Aar in southern Namibia significantly expands this data set, and the well preserved internal and external features on these specimens permit new interpretations of Rangea morphology and lifestyle. Internal structures of Rangea consist of a hexaradial axial bulb that passes into an axial stalk extending the length of the fossil. The axial bulb is typically filled with sediment, which becomes increasingly loosely packed and porous distally, with the end of the stalk typically preserved as an empty, cylindrical cone. This length of the axial structure forms the structural foundation for six vanes arranged radially around the axis, with each vane consisting of a bilaminar sheet composed of a repetitive pattern of elements exhibiting at least three orders of self-similar branching. Rangea was probably an epibenthic frond that rested upright on the sea bottom, and all known fossil specimens were transported prior to their final burial in storm deposits.