New fossil assemblages from the Early Ordovician Fezouata Biota

The Fezouata Biota (Morocco) is an exceptionally well-preserved fossil community of Early Ordovician age and although its oldest units are comparable with Burgess Shale-type localities of the Cambrian Explosion, little attention has been paid to the younger units despite potential to reveal the conditions of the Ordovician Radiation. Herein, we describe a new middle to upper Floian Fezouata locality (Taichoute) encompassing an assemblage dominated by large bivalved euarthropods and giant filter-feeding radiodonts, which were transported and preserved in concretions associated with density-flow deposits. Taichoute captures the closing of the taphonomic window that characterizes exceptional fossil preservation during the Cambrian Explosion (i.e., carbonaceous compressions) as well as the faunal transition to assemblages dominated by typical Palaeozoic taxa.

Chance, Evolution, and the Metaphysical Implications of Paleontological Practice

For several decades, a debate has been waged over how to interpret the significance of fossils from the Burgess Shale and Cambrian Explosion. Stephen Jay Gould argued that if the “tape of life” was rerun, then the resulting lineages would differ radically from what we find today, implying that humans are a happy accident of evolution. Simon Conway Morris argued that if the “tape of life” was rerun, the resulting lineages would be similar to what we now observe, implying that intelligence would still emerge from an evolutionary process. Recent methodological innovations in paleontological practice call into question both positions and suggest that global claims about the history of life, whether in terms of essential contingency or predictable convergence, are unwarranted.

Synchrotron imagery of phosphatized eggs in Waptia cf. W. fieldensis from the middle Cambrian (Miaolingian, Wuliuan) Spence Shale of Utah

Exceptionally preserved fossil eggs and embryos provide critical information regarding paleoembryogenesis, reproductive strategies, and the early ontogeny of early arthropods, but the rarity of preservation of both eggs and egg-bearing organisms in situ limits their use in detailed evolutionary developmental (evo-devo) studies. Burgess Shale-type deposits preserve rare instances of egg-bearing arthropods as carbonaceous compressions; however, the eggs are usually poorly preserved with no compelling evidence of embryos. We describe the first record of a brooding specimen of Waptia cf. W. fieldensis from the Spence Shale, a Cambrian (Wuliuan Stage) Burgess Shale-type deposit in northeastern Utah and southeastern Idaho. This is the first record of an egg-bearing arthropod from the Spence Shale and it exhibits two distinct modes of preservation among eggs within the single clutch: carbonization and phosphatization. Unlike the egg-bearing Burgess Shale specimens, many eggs of this Utah specimen are also preserved three-dimensionally. In addition, synchrotron radiation X-ray tomographic microscopy reveals internal distributions of mineral phases, along with potential remnants of the egg membrane and attachment structures, but, as in the Burgess Shale, no explicit traces of developing embryos. The distinct modes of preservation highlight the existence of diagenetic microenvironments within some eggs, but not in others during fossilization.

Differentiated appendages in Isoxys illuminate origin of arthropodization

The Cambrian fossil record has produced remarkable insights into the origin of euarthropods, particularly the evolution of their versatile body plan of segments bearing specialized, jointed appendages for different functions including feeding and locomotion [01, 02]. Early euarthropod evolution involved a major transition from lobopodian-like taxa [03, 04, 05] to organisms featuring a fully sclerotized trunk (arthrodization) and limbs (arthropodization) [02, 06, 07, 08]. However, the precise origin of arthropodization remains controversial because some of the earliest branching euarthropods possess a broad dorsal carapace that obscures critical details of the trunk and appendage organization [09, 10, 11, 12, 13, 14, 15]. Here, we demonstrate the presence of fully arthropodized ventral appendages in the upper stem-group euarthropod Isoxys curvirostratus from the early Cambrian Chengjiang biota in South China. Micro-computed tomography reveals the detailed three-dimensional structure of the biramous appendages in I. curvirostratus for the first time. In addition to the raptorial frontal appendages I. curvirostratus also possesses two batches of morphologically distinct biramous limbs, with the first batch consisting of four pairs of short cephalic appendages bearing prominent endites with a feeding function, followed by a second batch of elongate trunk appendages for locomotion. Each biramous limb bears an endopod with more than 12 well-defined podomeres, and an exopod consisting of a slender shaft carrying approximately a dozen paddle-shaped lamellae. Our findings clarify the enigmatic appendicular organization of Isoxys, one of the most ubiquitous euarthropods in Cambrian Burgess Shale-type deposits worldwide [01, 10, 11, 12, 14, 15, 16, 17, 18]. Critically, our new material shows that the trunk of I. curvirostratus was not arthrodized. The phylogenetic position of isoxyiids as possibly the earliest branching members of Deuteropoda [01, 02, 07, 15, 19], suggests that arthropodized biramous appendages evolved before the pattern of full trunk arthrodization that characterizes most extant and extinct members of this successful animal phylum.

A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity

Radiodonts, stem-group euarthropods that evolved during the Cambrian explosion, were among the largest and most diversified lower palaeozoic predators. These animals were widespread geographically, occupying a variety of ecological niches, from benthic foragers to nektonic suspension feeders and apex predators. Here, we describe the largest Cambrian hurdiid radiodont known so far, Titanokorys gainesi , gen. et sp. nov., from the Burgess Shale (Marble Canyon, Kootenay National Park, British Columbia). Estimated to reach half a metre in length, this new species bears a very large ovoid-shaped central carapace with distinct short posterolateral processes and an anterior spine. Geometric morphometric analyses highlight the high diversity of carapace shapes in hurdiids and show that Titanokorys bridges a morphological gap between forms with long and short carapaces. Carapace shape, however, is prone to homoplasy and shows no consistent relationship with trophic ecology, as demonstrated by new data, including a reappraisal of the poorly known Pahvantia . Despite distinct carapaces, Titanokorys shares similar rake-like appendages for sediment-sifting with Cambroraster, a smaller but much more abundant sympatric hurdiid from the Burgess Shale . The co-occurrence of these two species on the same bedding planes highlights potential competition for benthic resources and the high diversity of large predators sustained by Cambrian communities.

Evidence for microbially mediated silver enrichment in a middle Cambrian Burgess Shale-type deposit, Mackenzie Mountains, northwestern Canada

The Selwyn basin and Mackenzie platform of northwestern Canada house an array of mineral deposits and prospects that are rich in silver, including Neoproterozoic red-bed or Kupferschiefer-type Cu and lower Paleozoic sedimentary exhalative (SEDEX) and Zn-Pb deposits. Within this overall metallogenic setting, the middle Cambrian (Drumian) Rockslide Formation was deposited under a largely oxic water column on the platform-to-basin slope along the eastern side of the Selwyn basin. The formation includes an interval termed the Ravens Throat River Lagerstätte which is a localized Burgess Shale-type calcareous mudstone about 2 m thick that preserves soft-bodied fossils. The mudstone contains comparatively large amounts of organic carbon preserved as thin carbonaceous laminae and discontinuous seams, representing benthic microbial mats, the remains of cyanobacteria and algae that were living in the water column, fecal pellets, large coprolites, and degraded animal tissues. The upper part of the Rockslide Formation, including the fossiliferous interval, contains elevated concentrations of Ag, up to 0.47 ppm. Some of the Ag in the mudstone occurs as aggregates of elemental particles ~10 m in size preferentially on the carbonaceous material comprising the coprolites. This localized enrichment suggests bioaccumulation of Ag nanoparticles or Ag+ from the water column by microorganisms on the coprolites or degrading organic matter in them. The source of the Ag may have been from penecontemporaneous SEDEX metallogeny or from broadly related subsurface fluids in the Selwyn Basin that enriched the overlying seawater.

The Biography of the Earth

This chapter focuses on the first era of the Phanerozoic Eon (“visible life”), the Paleozoic Era, when life burgeoned after a rapid shift from a frozen setting during Snowball Earth times to dramatic warming related to greenhouse conditions. The chapter includes stories, such as that of the finding of the unique creatures of the Burgess Shale in Canada, that represent the diversity of life in the early part of the Paleozoic, the Cambrian Period. Several climatic shifts happened in the Paleozoic with resulting extinction events, the first occurring at the end of the Ordovician Period, the second at the end of the Devonian, and a third massive extinction at the end of the Permian Period. The latter was the largest extinction event ever recorded when 95 percent of all genera were killed as the supercontinent Pangea began to be split apart at the end of the Paleozoic.

Central nervous system of a 310-m.y.-old horseshoe crab: Expanding the taphonomic window for nervous system preservation

The central nervous system (CNS) presents unique insight into the behaviors and ecology of extant and extinct animal groups. However, neurological tissues are delicate and prone to rapid decay, and thus their occurrence as fossils is mostly confined to Cambrian Burgess Shale–type deposits and Cenozoic amber inclusions. We describe an exceptionally preserved CNS in the horseshoe crab Euproops danae from the late Carboniferous (Moscovian) Mazon Creek Konservat-Lagerstätte in Illinois, USA. The E. danae CNS demonstrates that the general prosomal synganglion organization has remained essentially unchanged in horseshoe crabs for >300 m.y., despite substantial morphological and ecological diversification in that time. Furthermore, it reveals that the euarthropod CNS can be preserved by molding in siderite and suggests that further examples may be present in the Mazon Creek fauna. This discovery fills a significant temporal gap in the fossil record of euarthropod CNSs and expands the taphonomic scope for preservation of detailed paleoneuroanatomical data in the Paleozoic to siderite concretion Lagerstätten of marginal marine deposits.

Three-dimensional modelling, disparity and ecology of the first Cambrian apex predators

Radiodonts evolved to become the largest nektonic predators in the Cambrian period, persisting into the Ordovician and perhaps up until the Devonian period. They used a pair of large frontal appendages together with a radial mouth apparatus to capture and manipulate their prey, and had evolved a range of species with distinct appendage morphologies by the Early Cambrian (approx. 521 Ma). However, since their discovery, there has been a lack of understanding about their basic functional anatomy, and thus their ecology. To explore radiodont modes of feeding, we have digitally modelled different appendage morphologies represented by Anomalocaris canadensis , Hurdia victoria , Peytoia nathorsti, Amplectobelua stephenensis and Cambroraster falcatus from the Burgess Shale. Our results corroborate ideas that there was probably a significant (functional and hence behavioural) diversity among different radiodont species with adaptations for feeding on differently sized prey (0.07 cm up to 10 cm). We argue here that Cambroraster falcatus appendages were suited for feeding on suspended particles rather than filtering sediment. Given the limited dexterity and lack of accessory feeding appendages as seen in modern arthropods, feeding must have been inefficient and ‘messy’, which may explain their subsequent replacement by crown-group arthropods, cephalopods and jawed vertebrates.