The Drumian Wheeler Konservat-Lagerst€ atte of the House Range of Utah (Wheeler-HR) has yielded one of the most diverse exceptionally preserved Cambrian biotas of North America. The discovery of soft-bodied fossils invariably provides precious insights into this biota, given that most of its non-biomineralizing components are known from very few specimens. This contribution describes some 30 new exceptionally preserved fossils of Wheeler panarthropods. Two new species are recognized, the radiodont Hurdia sp. nov. A and the megacheiran Kanoshoia rectifrons gen. et sp. nov. Along with a species of Leanchoilia, K. rectifrons represents the first confident megacheiran record in these strata. The presence of the radiodont genus Amplectobelua and the isoxyid species Isoxys longissimus is reported outside of the Burgess Shale in Laurentia. New specimens of Caryosyntrips serratus, Naraoia compacta, Messorocaris magna and Mollisonia symmetrica provide insights into the phylogenetic affinities, local spatial distribution and morphological variation of these species hitherto known by single specimens in the Wheeler-HR. The same is true of new materials of the more common Pahvantia hastata and Perspicaris? dilatus. Formal descriptions of the order Mollisoniida ord. nov. and family Mollisoniidae fam. nov. are also provided. Last, the preservation of body structures other than the dorsal exoskeletons is illustrated for the first time in two common components of the fauna: the agnostid Itagnostus interstrictus and the bivalved euarthropod Pseudoarctolepis sharpi. The new material substantially improves our understanding of the diversity of the Wheeler-HR biota, and provides new evidence of its distinctiveness relative to the Wheeler biota of the Drum Mountains.

The Red Queen hypothesis (RQH) is both familiar and murky, with a scope and range that has broadened beyond its original focus. Although originally developed in the palaeontological arena, it now encompasses many evolutionary theories that champion biotic interactions as significant mechanisms for evolutionary change. As such it de-emphasizes the important role of abiotic drivers in evolution, even though such a role is frequently posited to be pivotal. Concomitant with this shift in focus, several studies challenged the validity of the RQH and downplayed its propriety. Herein, we examine in detail the assumptions that underpin the RQH in the hopes of furthering conceptual understanding and promoting appropriate application of the hypothesis. We identify issues and inconsistencies with the assumptions of the RQH, and propose a redefinition where the Red Queen's reign is restricted to certain types of biotic interactions and evolutionary patterns occurring at the population level.

The Spence Shale Member of the Langston Formation is a Cambrian (Miaolingian: Wuliuan) Lagerstätte in northeastern Utah and southeastern Idaho. It is older than the more well-known Wheeler and Marjum Lagerstätten from western Utah, and the Burgess Shale from Canada. The Spence Shale shares several species with these younger deposits, yet it also contains a remarkable number of unique species. Because of its relatively broad geographical distribution, and the variety of palaeoenvironments and taphonomy, the fossil composition and likelihood of recovering weakly skeletonized (or soft-bodied) taxa varies across localities. The Spence Shale is widely acknowledged not only for its soft-bodied taxa, but also for its abundant trilobites and hyoliths. Recent discoveries from the Spence Shale include problematic taxa and provide insights about the nature of palaeoenvironmental and taphonomic variation between different localities. Supplementary material: A generic presence–absence matrix of the Spence Shale fauna and a list of the Spence Shale localities are available at: https://doi.org/10.6084/m9.figshare.c.4423145

A new Burgess Shale-type Lagerstätte is described from the middle Cambrian (Series 3, Drumian) Rockslide Formation of the Mackenzie Mountains, Northwest Territories, Canada. The Rockslide Formation is a unit of deeper water ramp to slope, mixed carbonate, and siliciclastic facies deposited on the northwestern margin of Laurentia. At the fossil-bearing locality, the unit onlaps a fault scarp cutting lower Cambrian sandstones. There it consists of a succession of shale and thick-laminated to thin-bedded lime mudstone, calcareous sandstone, and greenish-colored calcareous mudstone, overlain by shallower water dolostones of the Avalanche Formation, which is indicative of an overall progradational sequence. The Rockslide Formation is of similar age to the Wheeler and Marjum formations of Utah, belonging to theBolaspidellaBiozone. Only two 1 m thick units of greenish mudstone exhibit soft-bodied preservation, with most specimens coming from the lower interval. However, the biota is common but not as diverse as that of other Lagerstätten such as the Burgess Shale in its type area. The shelly fauna is dominated by the hyolithHaplophrentis carinatusMatthew, 1899 along with sparse linguliformean brachiopods, agnostoid arthropods, and ptychoparioid trilobites. The nonmineralized biota includes the macrophytic algaMargaretia dorusWalcott, 1911, priapulid worms, and the carapaces of a number of arthropods. The arthropods belong toIsoxys mackenziensisn. sp.,Tuzoiacf.T. guntheriRobison and Richards, 1981;Branchiocaris? sp.,Perspicaris?dilatusRobison and Richards, 1981; and bradoriids, along with fragments of arthropods of indeterminate affinities. The style of preservation indicates that most soft parts underwent complete biodegradation, leaving just the more resistant materials such as chitinous arthropod cuticles. The range of preservation and similarity to the coeval biotas preserved in Utah suggests that the composition of this Lagerstätte is probably representative of the community living on the relatively deep-water ramp or slope during middle Cambrian time in Laurentia. This would argue that the extraordinary diversity of the Burgess Shale at Mount Field is anomalous.

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The Middle Cambrian (series 3, Drumian, Bolaspidella Biozone) Ravens Throat River Lagerst€ atte in the Rockslide Formation of the Mackenzie Mountains, northwestern Canada, contains a Burgess Shale-type biota of similar age to the Wheeler and Marjum formations of Utah. The Rockslide Formation is a unit of deep-water, mixed carbonate and siliciclastic facies deposited in a slope setting on the present-day northwestern margin of Laurentia. At the fossil-bearing locality, the unit is about 175 m thick and the lower part onlaps a fault scarp cutting lower Cambrian sandstones. It consists of a succession of shale, laminated to thin-bedded lime mudstone, debris-flow breccias, minor calcareous sandstone, greenish-coloured calcareous mudstone and dolomitic siltstone, overlain by shallow-water dolostones of the Broken Skull Formation, which indicates an overall progradational sequence. Two~1-m-thick units of greenish calcareous mudstone in the upper part exhibit soft-bodied preservation, yielding a biota dominated by bivalved arthropods and macrophytic algae, along with hyoliths and trilobites. It represents a low-diversity in situ community. Most of the fossils occur in the lower unit, and only the more robust components are preserved. Branching burrows are present under the carapaces of some arthropods, and common millimetre-sized disruptions of laminae are interpreted as bioturbation. The fossiliferous planar-laminated calcareous mudstone consists of chlorite, illite, quartz silt, calcite and dolomite and is an anomalous facies in the succession. It was deposited via hemipelagic fallout of a mixture of platform-derived and terrestrial mud. Geochemical analysis and traceelement proxies indicate oxic bottom waters that only occasionally might have become dysoxic. Productivity in the water column was dominated by cyanobacteria. Fragments of microbial mats are common as carbonaceous seams. Complete decay of soft tissues was interrupted due to the specific sediment composition, providing support for the role of clay minerals, possibly chlorite, in the taphonomic process. □ Burgess Shale, Cambrian, Lagerst€ atte, Mackenzie Mountains, taphonomy.Julien Kimmig [jkimmig@gmail.com], and Brian R. Pratt [brian.pratt@usask.ca],

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Basal metabolic rate (BMR) is posited to be a fundamental control on the structure and dynamics of ecological networks, influencing organism resource use and rates of senescence. Differences in the maintenance energy requirements of individual species therefore potentially predict extinction likelihood. If validated, this would comprise an important link between organismic ecology and macroevolutionary dynamics. To test this hypothesis, the BMRs of organisms within fossil species were determined using body size and temperature data, and considered in the light of species' survival and extinction through time. Our analysis focused on the high-resolution record of Pliocene to recent molluscs (bivalves and gastropods) from the Western Atlantic. Species-specific BMRs were calculated by measuring the size range of specimens from museum collections, determining ocean temperature using the HadCM3 global climate model, and deriving values based on relevant equations. Intriguingly, a statistically significant difference in metabolic rate exists between those bivalve and gastropod taxa that went extinct and those that survived throughout the course of the Neogene. This indicates that there is a scaling up from organismic properties to species survival for these communities. Metabolic rate could therefore represent an important metric for predicting future extinction patterns, with changes in global climate potentially affecting the lifespan of individuals, ultimately leading to the extinction of the species they are contained within. We also find that, at the assemblage level, there are no significant differences in metabolic rates for different time intervals throughout the entire study period. This may suggest that Neogene mollusc communities have remained energetically stable, despite many extinctions.