Can. J. Earth Sci. 44: 367–387 (2007) doi:10.1139/E07-003 © 2007 NRC Canada 367 Spindle-shaped Ediacara fossils from the Mistaken Point assemblage, Avalon Zone, Newfoundland James G. Gehling and Guy M. Narbonne Abstract: The Mistaken Point assemblage of the Ediacara fossils is dominated by rangeomorphs with homologous fractal branching elements. The most distinctive are the fusiform fossils, herein named Fractofusus misrai n.gen., and n.sp., and Fractofusus andersoni n.gen., and n.sp. Although endemic to the Newfoundland portion of the Avalonia terrane, they dominated deep sea-floor communities below the photic zone, in the mid-Ediacaran Period (ca. 575– 560 Ma). Their biological affinities remain uncertain, but their architecture suggests a phylogenetic position near the base of the Metazoa. Résumé : L’assemblage de fossiles édiacariens de Mistaken Point est dominé par des rangeomorphes présentant des éléments homologues à embranchement fractal. Les plus distinctifs sont des fossiles fusiformes ici nommés Fractofu- sus misrai n.gen. et n.sp. et Fractofusus andersoni n.gen. et n.sp. Bien qu’ils soient endémiques à la portion terre- neuvienne du terrane d’Avalon, ils dominaient de communautés du fond marin profond sous la zone photique durant la période édiacarienne moyenne (v. 575–560 Ma). Leurs affinités biologiques demeurent incertaines, mais leur architec- ture laisse croire à une position phylogénétique près de la base des Métazoaires. [Traduit par la Rédaction] Gehling and Narbonne 387 Introduction Fossils of the Ediacara biota, best known from the Flinders Ranges in South Australia (Sprigg 1947; 1949), characterize the recently defined Ediacaran Period, the first Precambrian time division to be ratified with a Global Stratotype Section and Point (Knoll et al. 2006). Ediacara- type fossils occur mainly as centimetre- to metre-scale im- pressions of soft-bodied animals preserved underneath event beds of sandstone or volcanic ash (Narbonne 2005; Gehling et al. 2005). Some Ediacara-type fossils may represent stem groups of modern animal phyla (Gehling 1987, 1988; Conway Morris 1993; Gehling and Rigby 1996; Fedonkin and Waggoner 1997; Lin et al. 2006), whereas others appear to represent failed experiments in the early evolution of multicellular life (Seilacher 1992; Buss and Seilacher 1994; Narbonne 2004). The best-known example of the latter group are the rangeomorphs, an extinct high-order taxon character- ized by centimetre-scale fractally branching modules in decimetre- to metre-scale frondose, comb-like, or bush-like structures (Jenkins 1985; Narbonne 2004, 2005). The most distinctive, and by far the most common, rangeomorphs in the Mistaken Point assemblage are fossils colloquially known as “spindle-shaped fossils.” These were the first Ediacaran fossils ever discovered or figured from Mistaken Point (Anderson and Misra 1968) and spindles have been figured in virtually every subsequent paper on the Mistaken Point assemblage. Spindle-shaped fossils are endemic to the Avalon Zone of eastern Newfoundland, and large bedding surfaces throughout the Avalon and the northern Bonavista peninsulas (Fig. 1) are crowded with hundreds to thousands of specimens. The realization that Ediacara fossils occur well below strata bearing undoubted early Cambrian fossils, established their priority in the record of megascopic life on Earth. The discovery of the Charnwood Forest assemblage of the Ediacara biota in Leicester, England by Roger Mason (Ford 1958) confirmed the likely Precambrian position of these enigmatic fossils (Glaessner and Daily 1959) and stimulated a new phase of global research into the origins of animal life on Earth. Glaessner and Daily (1959) recognized that frondose fossils previously described by Gürich (1933) from southwestern Africa (Namibia) were of equivalent age. The discovery, a decade later, of the Mistaken Point assemblage (Anderson and Misra 1968; Misra 1969) in the Conception Group of southeastern Newfoundland greatly expanded the diversity of forms in the Ediacara biota. In the last 40 years, fossils of the Ediacara biota have been discovered on all continents except Antarctica. Received 20 December 2006. Accepted 23 January 2007. Published on the NRC Research Press Web site at http://cjes.nrc.ca on 21 May 2007. Paper handled by Associate Editor J. Jin. J.G. Gehling. 1,2 Department of Geological Sciences, Queen’s University, Kingston, ON K7L 3N6 Canada and Department of Earth Sciences, Monash University, Clayton, VIC, 3168 Australia. G.M. Narbonne. Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada; and Royal Ontario Museum, 100 Queen’s Park, Toronto, ON M5S 2C6, Canada. 1 Present address: South Australian Museum, North Terrace, Adelaide, SA, 5000 Australia. 2 Corresponding author (e-mail: gehling.jim@saugov.sa.gov.au).