Nicholas James Butterfield

The Ordovician saw one of the greatest evolutionary radiations in the Earth’s history, precipitating the assembly of modern animal-dominated ecologies in the aftermath of the Cambrian Explosion. However, Ordovician nonmineralized faunas are rare and mostly sample ecologically marginal settings. We describe small carbonaceous fossils (SCFs), including semiarticulated elements preserving submicrometric detail, from epicratonic deposits of the Deadwood and Winnipeg formations (ND). The Osterberg SCFs, associated with biostratigraphically informative conodonts and graptolites, record two successive biotas of Cambrian-Tremadocian (the “lower Osterberg” biota) and Darriwilian (the “upper Osterberg” biota) ages, demonstrating a long-term persistence of high-quality, Burgess Shale-type microfossil preservation after the end of the Cambrian. Their components open a window on normal marine, well-oxygenated Ordovician shelf habitats, revealing taxa and functional morphologies unrecorded by coeval macrofossils. These include specialized grazing and predatory molluskan radulae, triturative crustaceomorph molars, the oldest known eurypterid-type cuticles, and microphagous priapulid worms. The Osterberg fossils attest to an Ordovician co-occurrence of cryptic taxa and feeding adaptations, reminiscent of the most ecologically modern Cambrian biotas, alongside classic later-Paleozoic forms like colonial zooplankton and biomineralized early vertebrates. By contrast, they do not record classic Burgess Shale-style taxa typical of marginal or deeper-water Ordovician assemblages. These results demonstrate a lasting presence of cryptic, modern-style shelf faunas throughout the earliest Paleozoic, suggesting that exceptional Ordovician macrofossil sites are unrepresentative of the broader state of their coeval biosphere.

Exceptionally preserved fossil assemblages, or Konservat-Lagerstätten, open direct windows on non-biomineralized faunas that chronicle the Cambrian radiation of animal phyla. However, these assemblages do not typically capture the well-oxygenated, resource-rich environments sustaining most metazoan diversity in modern marine systems. We describe exceptionally preserved and articulated carbonaceous mesofossils from the middle Cambrian (~507 to 502 million years) Bright Angel Formation of the Grand Canyon (Arizona, USA). This biota preserves probable algal and cyanobacterial photosynthesizers together with a range of functionally sophisticated metazoan consumers: suspension-feeding crustaceans, substrate-scraping molluscs, and morphologically exotic priapulids with complex filament-bearing teeth, convergent on modern microphagous forms. The Grand Canyon’s extensive ichnofossil and sedimentological records show that these phylogenetically and functionally derived taxa occupied highly habitable shallow-marine environments, sustaining higher levels of benthic activity than broadly coeval macrofossil Konservat-Lagerstätten. These data suggest that evolutionary escalation in resource-rich Cambrian shelf settings was an important driver of the assembly of later Phanerozoic ecologies.

(SCFs) have disclosed a record of organically preserved faunas from Cambrian epeiric seas. Their phylogenetically and functionally derived components, including probable crown-group crustaceans and molluscs, are absent from the ‘exceptional’ palaeoenvironmental settings captured by Burgess Shale-type (BST) macrofossil biotas. This apparent segregation of SCF and BST-macrofossil deposits has led to contrasting hypotheses on whether their faunal differences reflect genuine ecological patterns or overriding taphonomic controls. We report a new, exceptionally diverse SCF biota from the Cambrian Hess River Formation of the Northwest Territories (Canada), which occupied an offshore slope setting. The Hess River biota, hosted by a single shale sample, rivals the Burgess Shale in its disparity of bilaterian body plans, providing a microfossil counterpoint to the regional record of BST-macrofossil faunas from similar deeper-water palaeoenvironments. The Hess River SCFs comprise exceptionally preserved ecdysozoan and spiralian sclerites, arthropod mouthparts, semi-articulated wiwaxiids, problematica and pterobranchs, but no recognizable crown molluscs or crustaceans. The similarities between the Hess River fauna and classic deeper-water BST-macrofossil biotas suggest significant palaeoecological overlap, robust to their distinct taphonomic expressions. This upholds the existence of comparatively modern communities in Cambrian epeiric settings, distinct from the faunas populating both BST-macrofossil biotas and SCF assemblages sampling similar palaeoenvironments.

Scalidophora, the ecdysozoan group including priapulids, kinorhynchs and loriciferans, comprises some of the most abundant and ecologically important Cambrian animals. However, reconstructions of the morphology and lifestyles of fossil scalidophorans are often hampered by poor preservation of their submillimetre-scale cuticular specializations. Based on exceptionally preserved small carbonaceous fossils (SCFs), we describe a new scalidophoran-grade animal, Scalidodendron crypticum gen. et sp. nov., from the Early to Middle Cambrian Hess River Formation of northern Canada. The Hess River SCFs comprise pharyngeal teeth, coniform sclerites and hook-like sclerites, all closely comparable to known scalidophoran counterparts. The coniform and hook-like sclerites recurrently associate with arborescent cuticular projections that show multiple orders of branching, morphologically unlike those of any known living or fossil scalidophoran. The fine splintering and inferred post-pharyngeal position of these structures argue against locomotory, feeding and defensive roles with direct analogues in extant counterparts. As such, the arborescent structures of Scalidodendron denote a previously cryptic range of morphological variation in Cambrian scalidophorans, paralleling that of coeval panarthropods but expressed at a fundamentally different level of anatomical organization.

Burgess‐Shale‐type (BST) faunas have proven critical for mapping the Cambrian assembly of animal‐dominated ecosystems, but have so far only been reported from fully subaqueous deposits. Here we integrate evidence from ichnofossils, sedimentary features, and small carbonaceous fossils (SCFs) from the middle Cambrian (Late Guzhangian, Series 3) Pika Formation of western Jasper National Park, Alberta (Canada) to document a unique BST fauna, occupying a peritidal habitat near the outer margin of a large epicratonic sea. Finely laminated shales with mudcracks and dumbbell‐shaped Arthraria ‐type burrows denote a periodically emergent, dysoxic mudflat setting. This same facies yields SCF priapulids, annelids and wiwaxiids typical of deeper‐marine sediments. Recovery of Cirratuliformia‐like annelid chaetae further identifies the likely source of Arthraria burrows and associated faecal pellets. These findings show that Cambrian marine metazoans, including probable members of crown‐group orders, ranged beyond permanently subaqueous deposits. The expanded palaeoenvironmental range of the BST taxa from the Pika biota denotes remarkably broad ecological tolerances, suggesting the existence of a guild of Cambrian metazoan generalists able to colonize at least transiently subaerial settings. Their occupation of offshore peritidal ecologies may have preluded to more extensive metazoan colonization of high‐energy, siliciclastic marginal marine environments.

Calcite, a CaCO 3 polymorph, is one of the most significant materials in nature. In addition to its fundamental role in the global carbon cycle, it fills an unparalleled range of applications, both as a natural biomineral and more directly engineered materials. One of the most notable characteristics of calcite is its tendency to form twins, the boundaries of which are expected to determine key attributes of the host mineral at mesoscopic scales. Using a classical molecular dynamics simulation performed with a thermodynamically consistent rigid-ion force field, we show that the walls between the two twin domains aligned along the hexagonal ( 10 1 ¯ 4 ) plane of calcite have some unexpected properties: (1) rather than monoatomic planes, these twin walls are composed of two layers with fundamentally different distortions, (2) atomic shifts within the twin walls create strong polarity while the bulk remains centrosymmetric, and (3) the temperature evolution of the structural order parameter is mostly, but not completely, related to the tilt and rotation of CO 3 2 − molecules. Molecular dynamics simulations using thermodynamically accurate interatomic potentials demonstrate that the temperature evolution of twin walls is different from that of the bulk material. We show that kinks in twin walls have a low energy and generate high structural disorder near the kink position. Our methods are applicable to other molecular systems and emphasize the dominance of twin walls in materials. Published by the American Physical Society 2024

Mandibulate arthropods (myriapods, hexapods and crustaceans) account for a major component of extant animal diversity but their origins remain unclear. Here, we re‐examine the record of exceptionally preserved arthropodan microfossils, including mandibles, from the lower Cambrian (Stage 4) Mount Clark Formation, Northwest Territories, Canada. The assemblage comes from a single drillcore horizon and occurs as thousands of small carbonaceous fossils (SCFs) representing disarticulated body parts. The mandibles occur as isolated molar surfaces with an elongate outline, a heavy setal fringe, and a subtle right–left asymmetry. These are sufficiently distinctive to diagnose a new genus and species of arthropod, Masticaris fimbriata. Co‐occurring SCFs include diverse appendage lobes and ventral body fragments, along with spines and setae assignable to 53 morphological categories and occurring either singly or in arrays, including filter plates. Most are plausibly interpreted as belonging to the feeding apparatus of M. fimbriata. The mandibles and filter plates correspond to those in extant pancrustaceans, particularly branchiopods, although the mouthparts of some more basal Cambrian arthropods raise the possibility of convergent feeding adaptations. Overall, anatomical and taphonomic continuity with younger SCFs suggests that M. fimbriata belongs to an early pancrustacean radiation that is still largely cryptic in the fossil record. More generally, the assemblage provides an inventory of fine‐scale cuticular specializations in early Cambrian arthropods that prefigure the trophic versatility and ecological dominance of crustaceans in the modern marine fauna.

Ediacaran rangeomorphs were the first substantially macroscopic organisms to appear in the fossil record, but their underlying biology remains problematic. Although demonstrably heterotrophic, their current interpretation as osmotrophic consumers of dissolved organic carbon (DOC) is incompatible with the inertial (high Re) and advective (high Pe) fluid dynamics accompanying macroscopic length scales. The key to resolving rangeomorph feeding and physiology lies in their underlying construction. Taphonomic analysis of three-dimensionally preserved Charnia from the White Sea identifies the presence of large, originally water-filled compartments that served both as a hydrostatic exoskeleton and semi-isolated digestion chambers capable of processing recalcitrant substrates, most likely in conjunction with a resident microbiome. At the same time, the hydrodynamically exposed outer surface of macroscopic rangeomorphs would have dramatically enhanced both gas exchange and food delivery. A bag-like epithelium filled with transiently circulated seawater offers an exceptionally efficient means of constructing a simple, DOC-consuming, multicellular heterotroph. Such a body plan is broadly comparable to that of anthozoan cnidarians, minus such derived features as muscle, tentacles and a centralized mouth. Along with other early bag-like fossils, rangeomorphs can be reliably identified as total-group eumetazoans, potentially colonial stem-group cnidarians.