EDIACARAN BIOTA ON BONAVISTA PENINSULA, NEWFOUNDLAND, CANADA

Journal of Paleontology, Jan 2008 by Hofmann, H J, O'Brien, S J, King, A F

Hiemalora stellaris FEDONKIN, 1994, fig. 1A.

Hiemalora cf. stellaris FEDONKIN, 1994, fig. 1C

Hiemalora stellaris SOKOLOV, 1997, p. 134-135, pl. 18, fig. 3.

Hiemalora MARTIN, GRAZHDANKIN, BOWRING, EVANS, FEDONKIN, AND KIRSCHVINK, 2000, p. 843-844, fig. 4D.

Hiemalora NARBONNE, DALRYMPLE, AND GEHLING, 2001, p. 33, 60, 65, 67.

Hiemalora pleiomorpha DZIK, 2003, p. 124, fig. 10B (only).

Description.-Discs on upper bedding surfaces, 0.3-4.8 cm wide (mean = 2.25 cm, n = 27), outlined by a distinct narrow raised rim ~0.5-1 mm wide surrounding a mostly flat disc with or without concentric ring. Attached to rim are numerous outwardly radiating, densely packed to moderately spaced narrow rays or appendages of variable length, generally of the order of the disc diameter or less, but in some specimens attaining double that (maximum observed length 5.2 cm, with average maximum of 3.15 cm for 27 specimens). Rays rectilinear to slightly sinuous, usually unbranched, but bifid and occasional trifid branching observed; rays rarely crossing over one another; 2 mm or less in width, slightly tapering distally to a point (as if descending obliquely into the sediment) or to a bulbous terminus (Fig. 9.1). In Figure 9.6, small specimen sitting on ray of larger specimen. In specimens illustrated in Figure 9.1-9.3, and 9.6, rays exhibiting shallow axial trough with curved semi-elliptical cross sections between narrow, levee-like lateral ridges; possible fusion of two filaments. Central disc bearing faint round outlines 3-5 mm across. Measurements of more complete specimens given in Figure 10.

Occurrence.-Mistaken Point Formation, Localities 2, 3, 5, 11, 35; Fermeuse Formation, Localities 16-18, 21, 24, 26, 29?, 38.

Discussion.-Inasmuch as the terms "tentacles" and "roots" used in the literature for the slender radiating appendages convey quite different anatomical features and functions, depending on one's interpretation of the body, it seems more appropriate to use the more neutral descriptive labels "rays" or "appendages" until meir function has been more convincingly demonstrated. While appendages in most specimens are unbranched, a few clearly exhibit branching.

The affinities of Hiemalora have been problematic. Their shape is not unlike that of the modern colonial cnidarian Obelia Peron and Lesueur, 1810. Fossils of this type from the Vendian (Ediacaran) of the White Sea region were originally referred to Pinegia and compared to solitary polyps of the lower Hydrozoa (Fedonkin, 1980). As the name Pinegia was preoccupied, the fossils were subsequently renamed Hiemalora (Fedonkin, 1982). Without being aware of these publications, Anderson and Conway Morris (1982) considered 3 alternatives for identical fossils in the Mistaken Point Formation-a basal attachment organ, a star-like trace fossil like Heliochone Seilacher and Hemleben, 1966, and a body fossil of unknown affinity. They favored the body fossil interpretation. An attachment organ was discounted, because the smooth ring was viewed as surrounding empty space, and no upward projections were observed. The trace fossil possibility was discarded because of the relationship between the structure and sediment and the mode of preservation. However, while most workers have considered them as cnidarians, the trace fossil interpretation was revisited by Martin et al. (2000). More recently, Dzik (2003, p. 125) regarded the structures as "basal discs of petalonamaeans or related organisms with finger-like protrusions functioning as roots, or possibly, as penetrating organs releasing sulfide from the microbial mat."