HYOLITHIDS, BACTERIA AND CESSPOOL PRESERVATION IN THE MIDDLE CAMBRIAN OF WESTERN CANADA

A horizon at the Glossopleura-Ehmaniella biozone boundary within the mid-Cambrian Stephen Formation (~505 Ma) has undergone a unique form of phosphatisation known as Cesspool preservation within Banff National Park, Alberta, Canada. A large number of specimens of the hyolithid Orthotheca sp. Novak, 1886 are preserved in great detail. The preservation includes unusual microstructures of the opercula as well as internal fecal pelletal linings within many of the conchs. Some of the conchs with this closely packed pelletal lining were also found to harbour exceptionally well preserved bacterial filaments which still retain a great degree of detail. The bacterial filaments are found in close association with the phosphatic fecal pellet lined conchs and may have been involved in the phosphatisation process. These filaments average 2-3 µm in width and have a non-branching, 'sausage-link' appearance of bacilli chains. The filaments were analysed using energy dispersive x-ray spectroscopy (EDS) and were found to preserve a high carbon signature. These bacterial remains may have been involved to some degree in symbiosis with Orthotheca sp. It is postulated that Orthotheca sp. may have engaged in a form of bacterial farming using the fecal pellets within the organism's conch. This may have provided a trophic energy transfer during intervals of reduced nutrient availability or may have allowed these organisms to inhabit a dysoxic environment as the hosted bacteria may have been thiotrophic. This possible symbiotic relationship could be one of the earliest representations of this type of behaviour in the rock record. Conchs within the deposit were also often found oriented with the apertural end angled upwards. This evidence concurs with earlier interpretations that orthothecids had an immobile, sedentary life habit and were likely suspension feeders.