MORPHOMETRIC ANALYSIS OF THE EDIACARAN FROND CHARNIODISCUS FROM THE MISTAKEN POINT FORMATION, NEWFOUNDLAND

Charniodiscus is one of the most widespread and best-known representatives of the Ediacara biota (terminal Neoproterozoic; 575-543 Ma). This soft-bodied, leaf-shaped organism consists of a segmented frond attached to a stem that was anchored to the seafloor by a basal attachment disc. Despite its worldwide distribution, the scarcity of complete specimens (fronds with stem and disc attached) has previously hindered evaluation of its taxonomy and biology. The presence of literally hundreds of complete Charniodiscus specimens from the Avalon Zone of Newfoundland has allowed for detailed morphometric analyses and construction of growth series of Charniodiscus, which permits the recognition of features that vary with growth (e.g. stem length, frond width, and disc diameter) versus those that reflect taxonomic differences (e.g. number of primary segments, presence of a distal spine, frond shape ratios). Ratio plots and principal components analyses (PCA) confirm the existence of five (possibly six) morphologically distinct species of Charniodiscus worldwide. Morphometrics distinguishes two feeding strategies within the Charniodiscus population at Mistaken Point Newfoundland. The first strategy consisted of building a large, wide frond with a short stem, thereby maximizing food gathering from the lower tiers. The second form sacrificed frond area in order to construct a longer stem that elevated the feeding structure above the lower tiers, permitting feeding up to 50 cm above the sea floor. By feeding from different tiers, the adult forms of both species effectively reduced the competition for resources and represent two similar, ecologically distinct forms of stalked filter feeders.