A new xenusiid lobopod from the early Cambrian Sirius Passet fauna of North Greenland

Three incomplete specimens of a large lobopod, Hadranax augustus gen. ct sp . nov. are described from the exceptionally preserved Sirius Passet fauna ( Buen Formation, Lower Cambrian, North Greenland). Its overall appearance an d size are similar to those of Xenusion auerswaldi Pompeckj from the Baltic , but H. augustus differs in its possession of four poorly defined dorsal n odes in each row rather than two, and in the probable possession of a pair of long, branched frontal appendages. The new specimens further demonstrate that the lobopods were a widespread and diverse Cambrian group. The presen ce of a four-noded xenusiid refutes the hypothesis that lobopods were direc tly derived from tetraradial nemathelminthes and shows that both node numbe r and form were fairly flexible, although their primary function remains un clear. The probable presence of a pair of long branched frontal appendages in H, augustus removes one of the major reasons for considering Xenusion to be a basal lobopod, and adds further to the characters that unite Anomaloc aris-like taxa to the lobopods.