ARCHANODON CATSKILLENSIS: HABITS, HABITATS, AND HISTORY

Study of Archanodon shell impressions, trace fossils, and associated depositional environments from localities in Devonian rocks of the Catskill Mountains and elsewhere suggest that these bivalves inhabited both freshwater floodplain and brackish estuarine environments. Morphological comparison with modern bivalves, particularly other unionoids, suggests that archanodonts were semi-infaunal suspension feeders. Their main nutrient source was undoubtedly current-borne particulate matter deriving from forest ecosystems then spreading over continental landscapes. Archanodon burrows can usually be distinguished from those of other animals in terms of size, shape and physical attributes. Experiments with modern unionid paradigms indicate that although Archanodon constructed meniscate escape burrows, their ability to escape anastrophic burial was greatly constrained. Archanodon escape burrows in Catskill terrestrial rocks represent responses to slow, periodic weather-related or temporal sediment deposition cycles, not to catastrophic single events. The biogeographic range of Archanodon is restricted to basins adjacent to the Acadian and Caledonian Highlands. The earliest known evidence of archanodonts are meniscate burrows in the Early Devonian of Wales. From here Archanodon spread southwestward with the advance of suitable habitats as the suturing of Laurentia, Baltica, and Avalon progressed southwestward during the Acadian Orogeny. The entry of Archanodon into Laurentia thus is coincident with the early phases of the Taghanic Biocrisis. Archanodon abundance and habitat diversity appears to diminish in the Late Devonian and Carboniferous. The extinction of Archanodon in the Late Carboniferous or Early Permian may be related to the proliferation of non-archanodont freshwater bivalves and freshwater durophagous predators which occurred at this time.