A suspension-feeding anomalocarid from the Early Cambrian

Tamisiocaris borealis , an Early Cambrian member of the anomalocarids—giant, predatory marine stem arthropods—probably used its frontal appendage to trap microscopic, planktonic animals. Plankton to spare for ancient shrimp-like filter feeder A broad range of marine predators, including sharks, rays, teleost fish and whales, have shown a transition to filter feeding, and this strategy has evolved independently several times in Earth's history. New fossils of Tamisiocaris borealis , from Early Cambrian sediments in northern Greenland, suggest that this large shrimp-like creature was also a free-swimming filter feeder, using its sizeable frontal appendages not to seize prey but more as combs, peaceably raking in the plankton. This is surprising because T. borealis is a member of the anomalocarids, normally thought of as the giant, predatory marine arthropods of Cambrian seas. The presence of such filter feeders in the Early Cambrian suggests that there were high densities of plankton available, which indicates the existence of a complex ecosystem in this period. Large, actively swimming suspension feeders evolved several times in Earth’s history, arising independently from groups as diverse as sharks, rays and stem teleost fishes 1 , and in mysticete whales 2 . However, animals occupying this niche have not been identified from the early Palaeozoic era. Anomalocarids, a group of stem arthropods that were the largest nektonic animals of the Cambrian and Ordovician periods, are generally thought to have been apex predators 3 , 4 , 5 . Here we describe new material from Tamisiocaris borealis 6 , an anomalocarid from the Early Cambrian (Series 2) Sirius Passet Fauna of North Greenland, and propose that its frontal appendage is specialized for suspension feeding. The appendage bears long, slender and equally spaced ventral spines furnished with dense rows of long and fine auxiliary spines. This suggests that T. borealis was a microphagous suspension feeder, using its appendages for sweep-net capture of food items down to 0.5 mm, within the size range of mesozooplankton such as copepods. Our observations demonstrate that large, nektonic suspension feeders first evolved during the Cambrian explosion, as part of an adaptive radiation of anomalocarids. The presence of nektonic suspension feeders in the Early Cambrian, together with evidence for a diverse pelagic community containing phytoplankton 7 , 8 and mesozooplankton 7 , 9 , 10 , indicate the existence of a comp