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Most sponges have biomineralized spicules. Molecular clocks indicate sponge classes diverged in the Cryogenian, but the oldest spicules are Cambrian in age. Therefore, sponges either evolved spiculogenesis long after their divergences or Precambrian spicules were not amenable to fossilization. The former hypothesis predicts independent origins of spicules among sponge classes and presence of transitional forms with weakly biomineralized spicules, but this prediction has not been tested using paleontological data. Here, we report an early Cambrian sponge that, like several other early Paleozoic sponges, had weakly biomineralized and hexactine-based siliceous spicules with large axial filaments and high organic proportions. This material, along with Ediacaran microfossils containing putative non-biomineralized axial filaments, suggests that Precambrian sponges may have had weakly biomineralized spicules or lacked them altogether, hence their poor record. This work provides a new search image for Precambrian sponge fossils, which are critical to resolving the origin of sponge spiculogenesis and biomineralization. Sponge animals likely originated in the Precambrian, but their early spicular fossils are ambiguous. Here, Tang et al. report a new Cambrian sponge taxon with weakly biomineralized spicules and suggest that the poor Precambrian record may reflect the later evolution of biomineralization.

Rocks of Ediacaran age (~635–541 Ma) contain the oldest fossils of large, complex organisms and their behaviors. These fossils document developmental and ecological innovations, and suggest that extinctions helped to shape the trajectory of early animal evolution. Conventional methods divide Ediacaran macrofossil localities into taxonomically distinct clusters, which may represent evolutionary, environmental, or preservational variation. Here, we investigate these possibilities with network analysis of body and trace fossil occurrences. By partitioning multipartite networks of taxa, paleoenvironments, and geologic formations into community units, we distinguish between biostratigraphic zones and paleoenvironmentally restricted biotopes, and provide empirically robust and statistically significant evidence for a global, cosmopolitan assemblage unique to terminal Ediacaran strata. The assemblage is taxonomically depauperate but includes fossils of recognizable eumetazoans, which lived between two episodes of biotic turnover. These turnover events were the first major extinctions of complex life and paved the way for the Cambrian radiation of animals. The Ediacara biota—the first large, complex organisms to evolve on Earth—disappeared prior to the radiation of animals during the Cambrian Period. Here, Muscente et al. perform network analysis of Ediacaran fossils and show that there were two global extinction events before the Cambrian radiation.

Morphology-based phylogenetic analyses support the monophyly of the Scalidophora (Kinorhyncha, Loricifera, Priapulida) and Nematoida (Nematoda, Nematomorpha), together constituting the monophyletic Cycloneuralia that is the sister group of the Panarthropoda. Kinorhynchs are unique among living cycloneuralians in having a segmented body with repeated cuticular plates, longitudinal muscles, dorsoventral muscles and ganglia. Molecular clock estimates suggest that kinorhynchs may have diverged in the Ediacaran Period. Remarkably, no kinorhynch fossils have been discovered, in sharp contrast to priapulids and loriciferans that are represented by numerous Cambrian fossils. Here we describe several early Cambrian (~535 million years old) kinorhynch-like fossils, including the new species Eokinorhynchus rarus and two unnamed but related forms. E. rarus has characteristic scalidophoran features, including an introvert with pentaradially arranged hollow scalids. Its trunk bears at least 20 annuli each consisting of numerous small rectangular plates and is armored with five pairs of large and bilaterally placed sclerites. Its trunk annuli are reminiscent of the epidermis segments of kinorhynchs. A phylogenetic analysis resolves E. rarus as a stem-group kinorhynch. Thus, the fossil record confirms that all three scalidophoran phyla diverged no later than the Cambrian Period.

Konservat-Lagerstätten—deposits with exceptionally preserved fossils—vary in abundance across geographic and stratigraphic space due to paleoenvironmental heterogeneity. While oceanic anoxic events (OAEs) may have promoted preservation of marine lagerstätten, the environmental controls on their taphonomy remain unclear. Here, we provide new data on the mineralization of fossils in three Lower Jurassic Lagerstätten—Strawberry Bank (UK), Ya Ha Tinda (Canada), and Posidonia Shale (Germany) —and test the hypothesis that they were preserved under similar conditions. Biostratigraphy indicates that all three Lagerstätten were deposited during the Toarcian OAE (TOAE), and scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) show that each deposit contains a variety of taxa preserved as phosphatized skeletons and tissues. Thus, despite their geographic and paleoenvironmental differences, all of these Lagerstätten were deposited in settings conducive to phosphatization, indicating that the TOAE fostered exceptional preservation in marine settings around the world. Phosphatization may have been fueled by phosphate delivery from climatically-driven sea level change and continental weathering, with anoxic basins acting as phosphorus traps.

Paleontologists routinely study fossils using high-magnification and high-resolution backscattered electron (BSE) images acquired via scanning electron microscopy (SEM). In BSE imaging, contrast corresponds to differences in backscattering of primary electrons and BSE detection among points in the electron beam raster scan. In general, BSE images are known for compositional contrast corresponding to backscattering monotonically related to average atomic number. However, two other types of contrast are relevant to BSE-SEM of fossils: (1) topographic contrast corresponding to backscattering and BSE detection varying with specimen shape and (2) mass-thickness contrast corresponding to backscattering varying with the relative masses and thicknesses of materials in the uppermost few microns of a sample. Here, we demonstrate the significance of these contrast mechanisms for resolving three-dimensional and subsurficial features of fossils. First, we show—through study of mass-thickness contrast in BSE images of carbonaceous compressions from the Triassic Solite Quarry Lagerstätte (Virginia)—that some tissues (e.g., leaf and insect wing veins) are preserved as thicker carbonaceous films than others (e.g., leaf laminae and insect wing membranes), possibly reflecting taphonomic differences among anatomical tissues. Second, we show that the problematic phosphatic shelly fossil Sphenothallus (lower Cambrian, China) is covered by low-relief transverse ribs and made up of exteriorly sculptured and interiorly unsculptured carbon- and phosphorus-rich layers with microstructures. Taking advantage of both topographic and mass-thickness contrast mechanisms, these case studies demonstrate that BSE imaging elucidates morphological details that are not obvious in surficial light microscopy or secondary-electron SEM and are otherwise only evident via tomography.

A new genus and species of the Elcanidae (Orthoptera, Elcanoidea), Cascadelcana virginiana n. gen. n. sp., is described based on a forewing specimen from the Upper Triassic (Norian) Cow Branch Formation in the Solite Quarry Lagerstätte near the North Carolina-Virginia boundary, USA. It is distinguished from other elcanid species by its RP +MA1 with six branches, M with two branches before stem MA1 fused with RP, and short CuA almost vertical against the posterior margin. This fossil represents the earliest definitive record of the family Elcanidae and the first orthopteran described from the Triassic of North America. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses show that the veins and a pterostigma-like structure on the wing of C. virginiana n. gen. n. sp. are preserved as carbonaceous compressions. The presence of a pterostigma-like structure in elcanids indicates that they may have evolved a particular flight mechanism distinct from those of other orthopterans.

The feather-shaped Plumalina Hall, 1858 is revised on the basis of new and reexamined specimens from New York. Previously described from Givetian through Famennian deposits, a single compression of P. tenera n. sp. from the Rochester Shale extends the range into the Wenlock, and provides new information regarding Plumalina's biology. We assess the utility of morphologic characters in diagnoses of taxa, and present the first quantitative analysis of fossil hydroids to distinguish P. brevis n. sp. (Frasnian) from other Devonian species. Plumalina has been compared to plants, graptolites, and octocorals. Some interpretations have proposed affinities among hydrozoans based on colony form and the presence of putative polyp bases. Our analysis shows that, like extant thecate hydrozoans, Plumalina had a delicate, chitinous hydrocaulus with weakly articulated hydrocladia. An assemblage of in situ specimens, steeply inclined relative to the bedding plane in an Ithaca Formation (Frasnian Stage) turbidite, indicates that Devonian species produced sessile, erect colonies attached to a hard substrate, comparable to extant hydroids that feed in currents. Morphometric comparisons between putative Plumalina polyp bases and polyp bases of modern analogues reveal similarities to hydroids in the superfamily Plumularioidea McCrady, 1859. Plumalina is the most abundant fossil hydroid so far reported, and is pertinent to interpretations of the hydrozoan record.

The Winneshiek Lagerstätte occurs within an Ordovician meteorite impact structure beneath part of the city of Decorah, Iowa. The Lagerstätte has yielded an atypical marine fauna including phyllocarid crustaceans, eurypterids, conodonts, linguloid brachiopods, and jawless fish. Associated with these taxa are vermiform fossils: elongate, morphologically variable, and often three-dimensionally preserved bromalites of uncertain organisms. The preservational state of these bromalites is significantly different from that of other components of the Winneshiek biota. Here we present a compositional and microstructural analysis of the vermiform fossils in order to elucidate their taphonomy and biological affinities. The majority of studied specimens are preserved three-dimensionally and composed of calcium phosphate, while a minority are preserved as carbonaceous compressions. Winneshiek bromalites exhibit important similarities to examples documented from both older and younger sediments. They provide independent evidence of predation in the Winneshiek assemblage during the Great Ordovician Biodiversification Event.

Mass extinctions documented by the fossil record provide critical benchmarks for assessing changes through time in biodiversity and ecology. Efforts to compare biotic crises of the past and present, however, encounter difficulty because taxonomic and ecological changes are decoupled, and although various metrics exist for describing taxonomic turnover, no methods have yet been proposed to quantify the ecological impacts of extinction events. To address this issue, we apply a network-based approach to exploring the evolution of marine animal communities over the Phanerozoic Eon. Network analysis of fossil co-occurrence data enables us to identify nonrandom associations of interrelated paleocommunities. These associations, or evolutionary paleocommunities, dominated total diversity during successive intervals of relative community stasis. Community turnover occurred largely during mass extinctions and radiations, when ecological reorganization resulted in the decline of one association and the rise of another. Altogether, we identify five evolutionary paleocommunities at the generic and familial levels in addition to three ordinal associations that correspond to Sepkoski’s Cambrian, Paleozoic, and Modern evolutionary faunas. In this context, we quantify magnitudes of ecological change by measuring shifts in the representation of evolutionary paleocommunities over geologic time. Our work shows that the Great Ordovician Biodiversification Event had the largest effect on ecology, followed in descending order by the Permian–Triassic, Cretaceous–Paleogene, Devonian, and Triassic–Jurassic mass extinctions. Despite its taxonomic severity, the Ordovician extinction did not strongly affect co-occurrences of taxa, affirming its limited ecological impact. Network paleoecology offers promising approaches to exploring ecological consequences of extinctions and radiations.

The hyperthermal events of the Cenozoic, including the Paleocene-Eocene Thermal Maximum, provide an opportunity to investigate the potential effects of climate warming on marine ecosystems. Here, we examine the shallow benthic marine communities preserved in the late Cretaceous to Eocene strata on the Gulf Coastal Plain (United States). In stark contrast to the ecological shifts following the end-Cretaceous mass extinction, our data show that the early Cenozoic hyperthermals did not have a long-term impact on the generic diversity nor composition of the Gulf Coastal Plain molluscan communities. We propose that these communities were resilient to climate change because molluscs are better adapted to high temperatures than other taxa, as demonstrated by their physiology and evolutionary history. In terms of resilience, these communities differ from other shallow-water carbonate ecosystems, such as reef communities, which record significant changes during the early Cenozoic hyperthermals. These data highlight the strikingly different responses of community types, i.e., the almost imperceptible response of molluscs versus the marked turnover of foraminifera and reef faunas. The impact on molluscan communities may have been low because detrimental conditions did not devastate the entire Gulf Coastal Plain, allowing molluscs to rapidly recolonise vacated areas once harsh environmental conditions ameliorated.