A Taphonomic Study of Early Triassic Fossil Fishes from Vega-Phroso Siltstone Member of the Sulphur Mountain Formation, British Columbia, Canada

The fossil fishes of the Vega-Phroso Member of the Sulphur Mountain Formation found near Wapiti Lake, British Columbia, represent some of the best preserved examples of Early Triassic ganoid fishes, and include the ray-finned actinopterygian Albertonia, Bobasatrania, Boreosomus, as well as the sarcopterygian, lobe-finned coelacanth, Whiteia. These fishes were deposited in an anoxic, offshore marine environment during the Early Triassic; as a result specimens are well-preserved, leading to superb preservation of scales, gills, and external soft tissue features. Excellent preservation of the fishes allows for the examination of decay and disarticulation processes that were active following death. A qualitative taphonomic ranking system was developed by classifying skull, fin and body decay and disarticulation into five stages, where Stage 1 indicates a perfectly-preserved specimen, while Stage 5 represents complete decay and disarticulation of a specimen. Initial observations suggest decay process began in the skull, and progressed throughout the body, with the caudal fin the last to decay. The progressive decay of the dorsal, pelvic and anal fins appears, however, to also depend on fish genera, mode of life, fin size, body length and body shape. In some of the least preserved fossils, the body appears distorted and bent into a J- or U- shape, suggesting the body became gas filled and was lifted off the seafloor, which resulted in some degree of post-mortem transport prior to deposition on the seafloor. Further research will determine the progression of decay within the different fish genera, and explain why some genera are better preserved than others. Taphonomic data from this study will be compared to other taphonomic fish studies, including fossil fish deposits, as well as taphonomy experiments of modern fishes run in the laboratory.