Re-evaluation of the morphology and systematic affinities of Corumbella werneri Hahn et al., Tamengo Formation (Ediacaran, Neoproterozoic), Corumbá, Brazil

Abstract

Analysis of specimens of the enigmatic Ediacaran fossil Corumbella werneri Hahn et al., from the Saladeira and Lajinha quarries (near Corumbá, Mato Grosso do Sul, SW Brazil) in the Tamengo Formation - Corumbá Basin, Paraguay Belt - revealed inconsistencies with the original morphological description. Features recorded so far in 50 specimens help elucidate the systematic position of Corumbella werneri within the Cnidaria or the "Vendobionta". Contrarily to the original species description, the present study could not verify such supposedly scyphozoan characters as the bipartite differentiation of the body and the presence of sclerosepta and attachment structures described by Hahn and others. Nevertheless, we have corroborated the oral-aboral organization and tetrarradial symmetry of the initial description. Besides these characteristics, the verification of budding in some specimens strengthens the hypothesis that these organisms were cnidarians, and not vendobionts. Examination of three-dimensionally preserved specimens suggests that the polyps were prismatic rather than cylindrical as described by the original authors and compared to the stephanocyphistoma of coronate scyphozoans. The specimens are segmented with smooth, convex/concave, subrectangular, slightly overlapping plates, which are wider than long and have slightly rounded borders. The arrangement of the plates conferred flexibility to the organisms, as is evident in longer specimens of C. werneri. Thus, on the basis of our present morphological analysis we can safely assign this taxon to the phylum Cnidaria. However, other attributes (e.g., attachment regions and the longitudinal and lateral arrangement of the plates) need to be evaluated in order to define more precisely the systematic position of this important fossil.