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Burgess Shale-type deposits are critical to our understanding of the Cambrian diversity explosion. Here, Caron et al.report a new assemblage from the middle Cambrian Burgess Shale, British Columbia, with high diversity and abundance of soft-bodied taxa, providing new insights into the early diversification of metazoans.

The 505-million-year-old Burgess Shales of British Columbia are justifiably famous for the exquisite preservation of their fossils, and for the extreme oddity of many of them. One such is Nectocaris pteryx, which, from the few fossils available for study, looked like a chordate fused with an arthropod. However, the collection and examination of more fossils of Nectocaris suggests that it in fact represents an early offshoot of cephalopod molluscs — a kind of squid, though with two rather than eight or ten tentacles.

Examination of a fossil enteropneust, Spartobranchus tenuis (Walcott, 1911), from the Cambrian-period Burgess Shale shows that they looked similar to modern enteropneusts but lived in tubes, like modern pterobranchs; the findings shed light on the common ancestor of enteropneusts and pterobranchs, and hence the origin of chordates.

Fossils of Metaspriggina, one of the earliest known and most primitive fishes, are described, with the structure of the gills shown to presage that of jawed vertebrates in many ways.

A re-analysis of the 508-million-year-old stem-group onychophoran Hallucigenia sparsa from the Burgess Shale shows that its anterior gut has structures that indicate evolutionary links with more disparate phyla such as nematodes and kinorhynchs; Hallucigenia now provides concrete evidence of structures that might have existed in the last common ancestor of the Ecdysozoa, previously a matter of conjecture.

Jean-Bernard Caron and Brittany Cheung provide new evidence that the rare Cambrian animal Amiskwia is closely related to gnathiferans, thereby resolving its ambiguous phylogeny. They describe new specimens from the Burgess Shale that preserve the complex jaw apparatus, which is most similar to gnathostomulids.

Tokummia katalepsis from the Burgess Shale had a pair of mandibles and maxilliped claws, showing that large bivalved arthropods from the Cambrian period are forerunners of myriapods and pancrustaceans, thereby providing a basis for the origin of the hyperdiverse mandibulate body plan.

Mollisonia plenovenatrix, a small predatory arthropod from the Burgess Shale dated to about 508 million years ago, is morphologically close to horseshoe crabs, which suggests chelicerates arose as micropredators early during the Cambrian explosion.

Analysis of exceptionally preserved fossils of the Cambrian hyolith Haplophrentis leads to a proposed evolutionary relationship with Lophophorata, the group containing brachiopods and phoronids, on the basis of a newly described tentacular feeding apparatus.

It requires a quirk of fossilization for the soft parts of an animal to be preserved. Study of such a specimen of the mysterious machaeridians provides these organisms with a well defined evolutionary home.