Until recently, intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerstätten. The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods, but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2-3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris. Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision--such as Anomalocaris--within the early Cambrian ecosystem probably helped to accelerate the escalatory 'arms race' that began over half a billion years ago.

The lower Cambrian Emu Bay Shale on Kangaroo Island, South Australia, contains the only known Cambrian Burgess Shale-type biota in Australia. Two new lamellipedian arthropods, Emucaris fava gen. et sp. nov. and Kangacaris zhangi gen. et sp. nov., from the Emu Bay Shale Lagerstätte are described as monotypic genera that are resolved cladistically as a monophyletic group that is sister to Naraoiidae + Liwiidae and classified within the Nektaspida as a new family Emucarididae. Shared derived characters of Emucarididae involve a bipartite, elongate hypostome and elongation of the pygidium relative to the cephalic shield and very short thorax. A monophyletic Liwiidae is composed of Liwia and the Ordovician Tariccoia + Soomaspis but excludes Buenaspis, and even the membership of Buenaspis in Nektaspida is contradicted amongst the shortest cladograms. New morphological interpretations favour affinities of Kwanyinaspis with Conciliterga rather than with Aglaspidida, and Phytophilaspis with Petalopleura.Key words: Arthropoda, Lamellipedia, Nektaspida, Emucaris, Kangacaris, phylogeny. Exploration and documentation of CambrianLagerstätten from around the globe have had a recent resurgence, with over 40 such biotas now being known (Conway Morris 1989, 1990 Hagadorn 2002; Zhu et al. 2006; Han et al. 2008; Gaines et al. 2008), including the lower Cambrian Emu Bay Shale Lagerstätte which was discovered by Brian Daily in the early 1950s at Big Gully, approximately 3 km east of Emu Bay on the north east coast of Kangaroo Island, South Australia (Text- fig. 1). To date, it is the only site in Australia that represents a Burgess Shale-type deposit containing an abundant and diverse biota; poorly preserved, soft-bodied remains, including Isoxys, are known from the lower Cambrian Heatherdale Shale on Fleurieu Peninsula, South Australia, but the biota has not been investigated in detail ( Earlier collections made from the Emu Bay Shale Lagerstätte -forming the basis of previous studies (see Paterson and Jago 2006, Paterson et al. 2008 for an overview) -have been sourced from the cliff and wave-cut platform exposures, which crop out on the shoreline immediately east of the mouth of Big Gully. In 2007, we commenced excavation of a new inland site, now referred to as Buck Quarry. Detailed information about this locality and the new collections, including a recent systematic revision of the bivalved arthropods Isoxys and Tuzoia, is provided by Paterson et al. (2008) and García-Bellido et al. (2009).The Nektaspida Raymond, 1920 is a group of lamellipedian euarthropods (i.e. taxa possessing broad paratergal folds and biramous limbs bearing flattened lamellar setae on comb-like exopods) with membership previously including Naraoia, Misszhouia, Liwia, Soomaspis, [Palaeontology, Vol. 53, Part 2, 2010, pp. 377-402] Tariccoia, Buenaspis, Pseudonaraoia, and possibly Maritimella and Orientella (sensu Hou and Bergström 1997; Budd 1999;. The nektaspids are stratigraphically long-ranging, from the lower Cambrian (Series 2, Stage 3;...

Exceptional fossil specimens with preserved soft parts from the Maotianshan Shale (ca 520 Myr ago) and the Burgess Shale (505 Myr ago) biotas indicate that the worldwide distributed bivalved arthropod Isoxys was probably a non-benthic visual predator. New lines of evidence come from the functional morphology of its powerful prehensile frontal appendages that, combined with large spherical eyes, are thought to have played a key role in the recognition and capture of swimming or epibenthic prey. The swimming and steering of this arthropod was achieved by the beating of multiple setose exopods and a flap-like telson. The appendage morphology of Isoxys indicates possible phylogenetical relationships with the megacheirans, a widespread group of assumed predator arthropods characterized by a pre-oral 'great appendage'. Evidence from functional morphology and taphonomy suggests that Isoxys was able to migrate through the water column and was possibly exploiting hyperbenthic niches for food. Although certainly not unique, the case of Isoxys supports the idea that off-bottom animal interactions such as predation, associated with complex feeding strategies and behaviours (e.g. vertical migration and hunting) were established by the Early Cambrian. It also suggests that a prototype of a pelagic food chain had already started to build-up at least in the lower levels of the water column.

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