Taphonomy and ontogeny of a multibranched Ediacaran fossil: Bradgatia from the Avalon Peninsula of Newfoundland

Abstract

Rangeomorphs, an extinct group of Ediacaran organisms with a fractal architecture and modular construction, occur abundantly in the Mistaken Point assemblage (575–560 Ma) of the Avalon Peninsula of Newfoundland. Bradgatia is represented by hundreds of specimens, collectively permitting analysis of its morphology, growth mode, and life habits. Bradgatia is a petalage that consists of a radial array of up to eight petals, each exhibiting up to four visible orders of rangeomorph branching. The taphonomy and ontogeny of Bradgatia are tightly linked by a change in preserved morphology, from juvenile I- to V-shaped specimens to larger U-shaped specimens, to the largest and ontogenetically oldest O-shaped specimens. Bradgatia probably maintained a constant number of petals that gradually spread out with age. The number of frondlets per petal does not correlate with length, suggesting either fractal or inflationary growth. Presence of a structure from which petals branch, abundance of contour-parallel specimens, differential preservation within specimens, and specimens overlying spindles and discs all imply that Bradgatia had an attached, epifaunal, suspension-feeding lifestyle. Bradgatia's multiple thin petals would have helped to filter water more efficiently, while its lack of a stem would have allowed for suspension feeding along the entire length of each petal.