Modular construction of early Ediacaran complex life forms

• Main Author: Guy M. Narbonne
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2004
• Subjects: Burrows; Canada; Mistaken Point; Newfoundland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.692.6296; http://geol.queensu.ca/people/narbonne/NarbonneScienceRangeomorphs2004.pdf

Newly discovered, exceptionally preserved, soft-bodied fossils near Spaniard’s Bay in eastern Newfoundland exhibit features not previously described from Ediacaran (ter-minal Neoproterozoic) fossils. All of the Spaniard’s Bay taxa were composed of similar architectural elements—centimeter-scale frondlets exhibiting three orders of fracti-cality in branching. Frondlets were combined as modules atop semi-rigid organic skeletons to formawide array of larger constructions, including frondose and plumose structures. This architecture and construction define the “rangeomorphs, ” a biological clade that dominated the Mistaken Point assemblage (575 to 560 million years ago) but does not appear to be ancestral to any Phanerozoic or modern organisms. The Ediacara biota is a distinctive fossil assem-blage of impressions of centimeter- to meter-scale, soft-bodied organisms that represent the oldest large and complex organisms and eco-systems in Earth history (1–3). The long-standing morphological view that the Ediacara biota contains the oldest animal megafossils is supported by the presence of probable animal embryos (4), burrows attributable to coelomic animals (5, 6), and a community organization that resembles that of modern suspension-feeding animals (7, 8). However, some Ediaca-ran taxa are more difficult to relate to living animal groups and have elicited interpretations that span virtually all extant kingdoms of mac-roscopic eukaryotes (9–11) as well as a hypoth-esized extinct kingdom (12). Fossils of the Mistaken Point assemblage (575 to 560 million years ago) in eastern Newfound-land, Canada (Fig. 1) represent the oldest reliably dated examples of the Ediacara biota (13–15). In contrast to younger Ediacaran assemblages from Australia and Russia, which contain segmented forms that are at least broadly comparable with modern animal phyla (16–18), the Mistaken Point assemblage is dominated by fossils exhibiting fractal-like quilting and whose relationships with modern taxa are not obvious at even the phylum