Burgess Shale fauna

A number of assemblages bear fossil assemblages similar in character to that of the Burgess Shale. While many are also preserved in a similar fashion to the Burgess Shale, the term "Burgess Shale type fauna" covers assemblages based on taxonomic criteria only.

The fauna of the middle Cambrian has a cosmopolitan range. All assemblages preserving soft-part anatomy have a very similar fauna, even though they span almost every continent. The wide distribution has been attributed to the advent of pelagic larvae.

The fauna is composed of a range of soft bodied organisms; creatures with hard, mineralised skeletons are rare, although trilobites are quite commonly found. The major soft-bodied groups are sponges, palaeoscolecid worms, lobopods, arthropods and anomalocaridids. Assemblages are typically diverse, with the most famous localities each containing in the region of 150 described species. The fauna of the Burgess Shale lived in the photic zone, as bottom-dwelling photosynthesisers are present in the assemblage.

Sirius Passet is a lagerstätte in Greenland which was formed about 527 million years ago. Its most common fossils are arthropods, but there is only a handful of trilobite species. There are also very few species with hard parts: trilobites, hyoliths, sponges, brachiopods, and no echinoderms or molluscs.

Halkieria has features associated with more than one living phylum, and is discussed below.

The strangest-looking animals from Sirius Passet are Pambdelurion and Kerygmachela. They are generally regarded as anomalocarids because they have long, soft, segmented bodies with a pair of broad fin-like flaps on most segments and a pair of segmented appendages at the rear. The outer parts of the top surfaces of the flaps have grooved areas which are thought to have acted as gills. Under each flap there is a short, fleshy leg. This arrangement suggests the animals are related to biramous arthropods.

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