Arthropod Visual Predators in the Early Pelagic Ecosystem Exemplified by Isoxys  

Fossil specimens with exceptionally preserved soft parts from the Maotianshan Shale (c. 520 Ma) and Burgess Shale (505 Ma) biotas indicate that the globally distributed bivalved arthropod Isoxys was probably a non-benthic visual predator.  We obtained new evidence from the functional morphology of its powerful prehensile frontal appendages which, in conjunction with large spherical eyes, are thought to have played a key-role in the recognition and capture of swimming or epibenthic prey.  Isoxys swam and steered using its flap-like telson while beating its multiple setose exopods.  The appendage morphology of Isoxys suggests a close relationship with the megacheirans, a widespread group of (probably) predatory arthropods characterized by a pre-oral ‘great appendage’.  Functional morphology and taphonomy both suggest that Isoxys was able to migrate through the water column, possibly exploiting hyperbenthic niches for food.  The palaeoecology of Isoxys supports the notion that off-bottom animal interactions, associated with complex feeding strategies and behaviours (e.g. vertical migration, hunting), were established by the Early Cambrian.  It also suggests that a prototype of pelagic food chain was already present, at least in the lower levels of the water column.