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Abstract The Cambrian Explosion saw the widespread development of mineralized skeletons. At this time, nearly every major animal phylum independently evolved strategies to build skeletons through either agglutination or biomineralization. Although most organisms settled on a single strategy,SalterellaBillings, 1865 employed both strategies by secreting a biocalcitic exterior shell that is lined with layers of agglutinated sediments surrounding a central hollow tube. The slightly older fossil,VolborthellaSchmidt, 1888, shares a similar construction with agglutinated grains encompassing a central tube but lacks a biomineralized exterior shell. Together these fossils have been grouped in the phylum Agmata Yochelson, 1977, although no phylogenetic relationship has been suggested to link them with the broader metazoan tree, which limits their contribution to our understanding of the evolution of shells in early animals. To understand their ecology and place them in a phylogenetic context, we investigatedSalterellaandVolborthellafossils from the Wood Canyon and Harkless formations of Nevada, USA, the Illtyd Formation of Yukon, Canada, and the Shady Formation of Virginia, USA. Thin-section petrography, acid maceration, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray tomographic microscopy were used to provide new insights into these enigmatic faunas. First, morphological similarities in the aperture divergence angle and ratio of central tube diameter to agglutinated layer thickness suggestSalterellaandVolborthellaare related. Second, both fossils exhibit agglutinated grain compositions that are distinctive from their surrounding environments and demonstrate selectivity on the part of their producers. Finally, the calcitic shell composition and simple layers of blocky prismatic shell microstructure inSalterellasuggest a possible cnidarian affinity. Together these data point to these organisms being sessile, semi-infaunal filter or deposit feeders and an early experimentation in cnidarian biomineralization chronicling a hypothesized transition from an organic sheath inVolborthellato a biomineralized shell inSalterella. 

Abstract The Mazon Creek Lagerstätte (Moscovian Stage, late Carboniferous Period; Illinois, USA) captures a diverse view of ecosystems in delta-influenced coastal settings through exceptional preservation of soft tissues in siderite concretions. The generally accepted paradigm of the Mazon Creek biota has been that of an inferred paleoenvironmental divide between what have been termed the Braidwood and Essex assemblages, wherein the former represents a freshwater ecosystem with terrestrial input and the latter a marine-influenced prodelta setting with abundant cnidarians, bivalves, worm phyla, and diverse arthropods. Here, we revisit the paleoecology of the Mazon Creek biota by analyzing data from nearly 300,000 concretions from more than 270 locations with complementary multivariate ordinations. Our results show the Braidwood assemblage as a legitimate shoreward community and provide evidence for further subdivision of the Essex assemblage into two distinct subassemblages, termed here the Will-Essex and Kankakee-Essex. The Will-Essex represents a benthos dominated by clams and trace fossils along the transition between nearshore and offshore deposits. The Kankakee-Essex is dominated by cnidarians, presenting an ecosystem approaching the geographic margin of this taphonomic window. These new insights also allow a refined taphonomic model, wherein recalcitrant tissues of Braidwood organisms were subject to rapid burial rates, while organisms of the Essex assemblage typically had more labile tissues and were subject to slower burial rates. Consequently, we hypothesize that the Braidwood fossils should record more complete preservation than the Essex, which was exposed for longer periods of aerobic decomposition. This is supported by a higher proportion of non-fossiliferous concretions in the Essex than in the Braidwood. 

The Smoky Hill Member of the Niobrara Chalk (Late Coniacian to Early Santonian), Kansas is renowned for its diverse assemblage of bromalites including coprolites, enterospirae, and even rare regurgitates. Producers of these fecal products are atributed to sharks, teleost fish and marine reptles based on their variously spiraled and non-spiraled morphologies, containing a range of invertebrate and vertebrate inclusions. Traditonally, examinaton of these fossils has necessitated sub-sampling via consumptve techniques like disaggregaton or dissoluton on either portons or the entrety of the specimen. Three-dimensional imaging techniques such as X-ray tomographic microscopy (µCT) offer a non-destructve alternatve to reveal both macroscopic and microscopic inclusions. Due to the minimal diagenetc alteraton of specimens from this locality, µCT imaging and segmentaton facilitates the extracton of structural and taphonomic informaton potentally obscured by physical extracton methods. This study employes non-destructve methods to explore the diversity of gross morphotypes represented by coprolites and a possible regurgitate from this member alongside their internal structure and inclusions. Preliminary results from segmented specimens offer insights into the taphonomic atributes of the coprolites and their ability to preserve exceptonally delicate structures, with remains of vertebral columns stll partally artculated. Lightly to non-mineralized inclusions, possibly crustaceans and scale remains, represent a hidden component of the assemblage rarely preserved otherwise. Virtual renders also enable quanttatve analysis of the inclusions with respect to the degrees of fragmentaton, the orientaton and alignment of boney inclusions relatve to the longitudinal axis of the specimen, and the relatve proportons of bone, pore space, and phosphatc matrix. This work offers a rare glimpse into the feeding, digestve, and excretory behaviors of producers whilst simultaneously capturing unique paleoecological and paleoenvironmental informaton. 

While molecular clock studies suggest a Tonian-Cryogenian (~800–635 Ma) emergence of the Porifera, convincing fossil evidence of sponges is seen only as far back as ~530 Ma. The >100 Ma lacuna for sponges represents a critical missing piece of the Neoproterozoic puzzle. Assembling an evolutionary framework requires that Poriferan antiquity be understood in terms of sponge form and function, and the emergence of suspension-feeding amid profound environmental and climatic change. Here we report newly discovered biomineralized fossils of sponge-grade animals in Neoproterozoic carbonates of Siberia, Australia, and Brazil. Using a wide range of petrographic, eProbe, µXRF, µCT, and serial grinding techniques, the sponge-grade fossils are shown to be remarkably preserved in three dimensions, displaying broad morphological characters associated with early experiments in biomineralization such as siliceous spicules and external carbonate shells. Reconstructions of their bauplan reveal forms evolutionarily equipped for a suspensionfeeding lifestyle, well-prepared for pumping seawater through their bodies. As ecosystem engineers that clarified the water column and allowed for greater depths of photosynthetic activity, the emergence (and dominance) of sponge-grade animals in shallow marine carbonate reefs had the potential to drive environmental change that is arguably recorded during extremes in the Neoproterozoic carbon cycle. With their global distribution, these animals would link the planktic and benthic realms for the first time in Earth history and represent a sink for the photosynthetically derived organic matter that impacted the oxidation state of the oceans and atmosphere. Notably, most of these fossils are archived in carbonates preserving global expressions of profoundly negative δ13C perturbations. These include the Ediacaran Period Shuram Excursion, which foreshadowed the widespread appearance of the Ediacara biota, and the terminal Cryogenian Period Trezona Anomaly, which immediately preceded the Marinoan snowball Earth. 

Abstract The terminal Ediacaran Period is signaled worldwide by the first appearance of skeletonizing tubular metazoan fossils, e.g.,CloudinaGerms, 1972 andSinotubulitesChen, Chen, and Qian, 1981. Although recent efforts have focused on evaluating the taxic composition and preservation of such assemblages from the southwestern United States, comparable forms reported in the 1980s from Mexico remain to be re-examined. Here, we reassess the latest Ediacaran skeletal materials from the La Ciénega Formation of the Caborca region in Sonora, Mexico, using a combination of analytical methods: optical microscopy of extracted fossils, thin-section petrography, scanning electron microscopy and energy dispersive X-ray spectroscopy, and X-ray tomographic microscopy. From our examination, we conclude that the La Ciénega hosts a polytaxic assemblage of latest Ediacaran tubular organisms that have been preserved through two taphonomic pathways: coarse silicification and calcareous recrystallization preserving finer details. Further, these fossils show signs that their shells might not have been inflexible or completely mineralized in vivo, and that they might also record tentatively interpreted predation traces in the form of drill holes or puncture marks. This work, along with ongoing efforts around the world, helps to provide a framework for biostratigraphic correlation and possible subdivision of the Ediacaran Period, and further shapes our view of metazoan evolution and ecology in the interval directly preceding the Cambrian explosion. 

The Eocene Pipestone Springs Main Pocket (Renova Formation, Jefferson County, Montana, United States of America) is a locality renowned for its diverse Chadronian (late Eocene; ∼38–33.9 million years ago) mammalian fauna and abundant coprolites. Two distinct coprolite size classes were previously identified in the trace fossil assemblage from which we selected representatives to investigate feeding behaviors and dietary selection of the producers. A subset of the selected coprolites was analyzed based on their compositional and taphonomic attributes using non-destructive x-ray tomographic microscopy in combination with more traditional methods including thin-section petrography, scanning electron microscopy, and energy dispersive spectroscopy. Among the features extracted in the tomographic data were skeletal fragments, including those showing evidence of bone-crushing; delicate hair molds; encrusted lithic fragments; and several irregular pores and cracks throughout the coprolites. Segmentation and volumetric renders permit quantitative assessment of the relative proportions of inclusions, revealing porosity as a primary volumetric element aside from the matrix and bone inclusions. There was no significant difference in the total volume of bone extracted between coprolite size class, though the smaller coprolites preserved a relatively higher volumetric proportion of undigested skeletal material. This multi-visualization approach provides a means to observe and evaluate differences in the coprolite gross morphology and inclusions across the two size classes, thereby offering valuable insights into the broader paleoecology of the Pipestone Springs Main Pocket coprolite producers and holding promise for comparable paleo-dietary studies of other coprolite-rich deposits. 

First described as a medusoid jellyfish, the “star-shaped” Brooksella from the Conasauga shale Lagerstätten, Southeastern USA, was variously reconsidered as algae, feeding traces, gas bubbles, and most recently hexactinellid sponges. In this work, we present new morphological, chemical, and structural data to evaluate its hexactinellid affinities, as well as whether it could be a trace fossil or pseudofossil. External and cross-sectional surfaces, thin sections, X-ray computed tomography (CT) and micro-CT imaging, revealed no evidence that Brooksella is a hexactinellid sponge or a trace fossil. Although internally Brooksella contains abundant voids and variously orientated tubes consistent with multiple burrowing or bioeroding organisms, these structures have no relation to Brooksella’s external lobe-like morphology. Furthermore, Brooksella has no pattern of growth comparable to the linear growth of early Paleozoic hexactinellids; rather, its growth is similar to syndepositional concretions. Lastly, Brooksella , except for its lobes and occasional central depression, is no different in microstructure to the silica concretions of the Conasauga Formation, strongly indicating it is a morphologically unusual endmember of the silica concretions of the formation. These findings highlight the need for thorough and accurate descriptions in Cambrian paleontology; wherein care must be taken to examine the full range of biotic and abiotic hypotheses for these compelling and unique fossils. 

ABSTRACT Laboratory-based decay experiments have become commonly used to supplement our understanding of how organisms enter the fossil record. Differences in how these experiments are designed and evaluated, however, including dissimilarities in qualitative decay-scoring indices superimposed on variability in model organisms, renders any semblance of comparison between studies unreliable. Here, we introduce the utility of X-ray tomographic microscopy (μCT) as a means for reliable and repeatable analysis of soft-tissue decay experiment products. As proof-of-concept, we used a relatively simple experimental design with classic studies as comparators, and present our analytical protocol using μCT for capturing the entire volume of the decay subject. Segmentation software then allows for 3D volume analysis and high-resolution internal and external character identification. We describe the workflow from sample preparation, contrast-staining, and data collection to processing and analysis of the resulting data, using peppermint shrimp (Lysmata wurdemanni) as model organisms, and compare our results to previous taphonomic studies. These methods allow for improved visualization and quantification of decay and internal volume analysis with minimal handling as compared to traditional qualitative scoring methods. Using the same scoring criteria as previous studies, this study revealed similar decay results for certain features, while we were additionally able to detect other feature loss or alteration earlier—importantly without need for potentially distortive sample handling. We conclude that μCT is a more effective, straightforward, and exact means for extracting quantitative data on the progression of decay and should be adopted in future studies, where available, to streamline and standardize comparisons. 

Abstract The fossil record of the terminal Ediacaran Period is typified by the iconic index fossilCloudinaand its relatives. These tube-dwellers are presumed to be primitive metazoans, but resolving their phylogenetic identity has remained a point of contention. The root of the problem is a lack of diagnostic features; that is, phylogenetic interpretations have largely centered on the only available source of information—their external tubes. Here, using tomographic analyses of fossils from the Wood Canyon Formation (Nevada, USA), we report evidence of recognizable soft tissues within their external tubes. Although alternative interpretations are plausible, these internal cylindrical structures may be most appropriately interpreted as digestive tracts, which would be, to date, the earliest-known occurrence of such features in the fossil record. If this interpretation is correct, their nature as one-way through-guts not only provides evidence for establishing these fossils as definitive bilaterians but also has implications for the long-debated phylogenetic position of the broader cloudinomorphs.