Sirius Passet is a Cambrian Lagerstätte in Greenland. The Sirius Passet Lagerstätte was named after the Sirius sledge patrol that operates in North Greenland. It comprises six localities located on the eastern shore of J.P. Koch Fjord in the far north of Greenland. It was discovered in 1984 by A. Higgins of the Geological Survey of Greenland. A preliminary account was published by Simon Conway Morris and others in 1987, but since then, expeditions led by J. S. Peel and Simon Conway Morris have returned to the site several times between 1989 and the present. A field collection of perhaps 10,000 fossil specimens has been amassed. The fauna is inevitably compared to that of the Burgess Shale, although it is probably ten to fifteen million years older – 518 vs. 505 Ma (Martin et al. 2000; Nevadella zone, stage 3 of Cambrian Series 2) – and more closely contemporaneous with that from Chengjiang. Although the fauna has not yet been fully described, it is known to consist of a moderate number of arthropods and sponges, together with rare representatives of other groups. It has yielded three highly problematic taxa, Halkieria, Kerygmachela and Pambdelurion, all of which have played prominent roles in discussions about the origins of the modern animal phyla. In early 2008, Simon Conway Morris published another paper describing a polychaete annelid from the Sirius Passet. As SCM et al. note in their discussion, "the phyletic position of Phragmochaeta is very poorly constrained, but it may be fairly basal", which is what makes these early Cambrian Lagerstätte so fascinating. Polychaete annelids are a significant component of the Burgess Shale fauna, but are otherwise unknown from the other early Cambrian Lagerstätte, so this single species from a single locality appreciably extends the depth of understanding of this group. Unfortunately, the material so far described from Sirius Passet is sparse in morphological characters. Simon Conway Morris notes in this most-recent paper that the study is being done on "almost 6000 fossiliferous slabs ... selected during visits between 1985 and 2006 from extensive talus slopes derived from the lower part of the Buen Formation", with indications that other outcrops of potentially fossiliferous material are known, but are under-explored. Isoxys was the most commonest animal on this shale.