RELICT ECOSYSTEMS AT THE DAWN OF THE PHANEROZOIC REVOLUTION

BUATOIS, L.A.; NARBONNE, G.M.; MÁNGANO, M.G.; CARMONA, N.B.; MYROW, P.

Mendoza

Congreso; International Paleontological Congress; 2014

The earliest Cambrian was a time of dramatic biological and sedimentary changes, including the replacement of Proterozoic-style microbial matgrounds by Phanerozoic-style bioturbated mixgrounds. However, Ediacaran-style matground-based ecology persisted into the earliest Cambrian. Our study in the type section of the basal Cambrian in Fortune Head, Newfoundland, Canada reveals widespread microbially induced sedimentary structures (e.g., wrinkle marks, gas domes) and typical Ediacaran-type matground trace fossils (e.g., grazing rails). Ediacara-type body fossils (e.g., Palaeopaschichnus) are present immediately below the top of the Ediacaran but are strikingly absent from the overlying Cambrian succession, despite optimal conditions for their preservation, and instead the microbial surfaces are marked by the appearance of the first abundant arthropod scratch marks (Allocotichnus dyeri) in the stratigraphic record. This combination of a microbial matground-based ecology, and the appearance of new body plans and associated locomotion mechanisms, actually resulted in a peak in diversity of animal-matground interactions during the Fortunian. These features imply that the disappearance of the Ediacara biota represents an abrupt evolutionary event that corresponded with the appearance of novel bilaterian clades, rather than a fading away due to the gradual elimination of conditions appropriate for Ediacaran preservation.