Early Cambrian Food Chain: New Evidence from Fossil Aggregates in the Maotianshan Shale Biota, SW China
Résumé
Three categories of fossil aggregates are recognized in the Lower Cambrian Maotianshan Shale biota from SW China: (1) elliptical aggregates with randomly distributed exoskeletal remains of typically small- to medium-size bivalved arthropods (e.g., ostracode-like bradoriids, phyllocarid- like waptiids), hyoliths, and trilobites are interpreted as coprolites, possibly produced by anomalocaridids (e.g., waptiid-rich coprolites) and/or unknown epibenthic predators; (2) elongate, ribbon-like aggregates composed of oriented small hyolith shells, interpreted as the feces of infaunal carnivorous worms such as priapulids; and (3) concentric aggregates, typically with a central nucleus (e.g., remains of medusoid eldoniids or bivalved arthropod carapaces) and peripheral exoskeletal fragments, possibly generated by bottom currents whirling around carcasses. These new coprolite data add to morphofunctional information obtained from fossil organisms and indicate that predation occurred at different levels of the water column with: (1) endobenthic predators (diverse priapulid fauna) feeding near the sediment-water interface; (2) epibenthic predators/scavengers (almost exclusively arthropods); (3) predators living in the lower levels of the water column (e.g., anomalocaridids); and (4) mid-water predators exploiting upper levels in the water column (e.g., eldoniids, ctenophores, chaetognaths). Communities living at or close to the water-sediment interface (epibenthic sensu stricto, meiobenthic, and demersal animals) were exposed to a multidirectional predatorial pressure from infaunal, epifaunal, and mid-water predators. Although predation was diverse, nothing indicates that the food chain extended beyond the level of primary carnivores. Animals already had acquired complex behaviors such as hunting (e.g., anomalocaridids, priapulids) and predator avoidance in which sensory systems were involved. The example of theMaotianshan Shale indicates that the burst of anatomical innovations (new body plans) that characterizes the early Cambrian alsowas accompanied by the rapid development of new feeding strategies and by an unprecedented expansion of ecological interactions (prey-predator relationships).