Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact email@example.com with any questions.
Broad-scale analyses of Cambrian spiculate sponges are scarce. The apparent differences between Cambrian and Ordovician sponge faunas were included in Sepkoski's concept of evolutionary faunas; in these, sponges were regarded as minor contributors to the Paleozoic and modern faunas and insignificant in the Cambrian Evolutionary Fauna. More recent published occurrences of Cambrian and Ordovician spiculate sponges and the inclusion of archaeocyaths in the phylum Porifera, however, have altered our understanding of the significance of sponges among Cambrian faunas. The majority of Cambrian occurrences appear to be segregated into two major associations: lower Cambrian sponges in China, and middle Cambrian sponges in North America, primarily British Columbia and Utah. The main associations of spiculate sponges are in siliciclastic deposits from middle-to-deep muddy shelf and basin environments, whereas orchoclad demosponges are associated with shallow carbonate environments. Four main aspects of sponge biology are considered potential factors dictating the distribution of sponges in the Cambrian: their trophic requirements, hydrodynamic constraints, possible biogeochemical constraints, and the sponge-sediment relationship. A series of critical steps in sponge evolutionary history occurred during the interval from the Proterozoic-Cambrian boundary to the middle– late Ordovician. The lower–middle Cambrian faunas are considered to be a Cambrian evolutionary sponge fauna, with archaeocyaths and diverse monaxonid demosponges as distinctive components. There was a transitional fauna in the upper Cambrian–Lower Ordovician, with orchoclad lithistids dominating shallow environments. Hexactinellids began to colonize nearshore siliciclastic settings during this time. The third interval, Middle–Upper Ordovician, corresponds to the Paleozoic Evolutionary Fauna, which is the interval during which lithistids diversified in several suborders and families and the stromatoporoid and sphinctozoan calcified sponges experienced their first radiation.
Repeated sequences of carbonate and shale are punctuated by condensed sections of phosphatic conglomerate in the epeiric deposits of the Trans-Saharan Seaway in northeastern Mali. To characterize the taphonomic and depositional setting of these phosphates, a thick Eocene conglomerate from the area of Tamaguélelt was targeted for quantitative analysis. Systematic grid sampling demonstrates that nearly all of the clasts are derived from vertebrate sources (bones = 27%, coprolites = 20%, probable coprolites = 53%), and invertebrate body fossils are nearly absent. Bony and cartilaginous fish dominate the bone assemblage, which also includes minor reptilian elements from sea turtles, sea snakes, and dyrosaurid crocodilians. Coprolites are of five distinct varieties, including three spiral forms probably produced by separate fish taxa. Repeated episodes of abrasion and minor bioerosion with modest levels of sorting characterize the taphonomy of the phosphate conglomerate and are consistent with a shallow-marine-to-brackish-water depositional environment between fair-weather and storm-wave base. Early phosphogenesis strongly favored the preservation and lithification of phosphate-rich bones and coprolites, probably during periods of marine transgression and sediment starvation. Combined with evidence from sedimentology, these vertebrate-dominated fossil assemblages appear extensively reworked and highly time averaged as a result of amalgamation and concentration by storm activity during periods of marine transgression.
A large dinosaur bone bed has been investigated in the Udurchukan Formation (?late Maastrichtian) at Blagoveschensk, Far Eastern Russia. The observed mixture of unstratified fine and coarse sediments in the bone bed is typical for sediment-gravity-flow deposits. It is postulated that sediment gravity flows, originating from the uplifted areas at the borders of the Zeya-Bureya Basin, reworked the dinosaur bones and teeth as a monodominant bone bed. Fossils of the lambeosaurine Amurosaurus riabinini form >90% of the recovered material. The low number of associated skeletal elements at Blagoveschensk indicates that the carcasses were disarticulated well before reworking. Although shed theropod teeth have been found in the bone bed, <2% of the bones exhibit potential tooth marks; scavenging activity was therefore limited, or scavengers had an abundance of prey at hand and did not have to actively seek out bones for nutrients. Perthotaxic features are very rare on the bones, implying that they were not exposed subaerially for any significant length of time before reworking and burial. The underrepresentation of light skeletal elements, the dislocation of the dental batteries, and the numerous fractured long bones suggest that most of the fossils were reworked. The random orientation of the elements might indicate a sudden end to transport before stability could be reached. The size-frequency distributions of the femur, tibia, humerus, and dentary elements reveal an overrepresentation of late juveniles and small subadult specimens, indicative of an attritional death profile for the Amurosaurus fossil assemblage. It is tentatively postulated that the absence of fossils attributable to nestling or early juvenile individuals indicates that younger animals were segregated from adults and could join the herd only when they reached half of the adult size.
Body size is one of the most significant organismal characteristics because of its strong association with nearly all important ecological and physiological characteristics. While direct body mass measurement (or estimation from other size metrics) is not feasible with most extinct taxa, body volume is a measurable and general proxy for fossil size. This study explores the reliability of several metrics that can be used to estimate the body volume of Paleozoic invertebrates of various sizes, shapes, taxonomic affinities, and ecological habits. The ATD model, based on the product of lengths of the three major body axes (anteroposterior, transverse, and dorsoventral), is simple and widely applicable. Models specific to particular morphological and taxonomic groups are slightly more accurate than this ATD model, but the advantages are minor. The ATD model is consistent with previous studies demonstrating widespread shape allometry—that is, small taxa tend to have globose geometries while large ones tend to be conical, even within the same taxonomic group. The ATD model successfully predicts the volume of 10 validation samples that were excluded from development of the original model. Because the linear measurements used to estimate volume are easy to obtain from specimens in the field or from published work, estimates of body volume can be incorporated into paleontological analyses, even those spanning multiple phyla.
Regional correlation of mudrock-siliciclastic units is challenging, largely owing to the apparent featurelessness of fine-grained intervals. This difficulty is multiplied when subsurface correlation is necessary for paleogeographic reconstruction. In this study, faunal-marker tracing and limestone-pattern matching have permitted subsurface correlation of the Alexandria submember of the Kope Formation (Edenian Stage, Upper Ordovician) over a 193-km transect in southwest Ohio. The faunal markers are thin (<10 cm), widespread deposits of skeletal debris exhibiting faunal associations, degrees of preservation, or both, that distinguish them from other fossil deposits in host mudrocks. Subsurface correlations corroborate interpretations of southwest Ohio paleogeography and demonstrate the usefulness of techniques presented here. Geographic trends in the data indicate that the average seafloor slope over much of the Cincinnati region was near zero. Evidence also indicates a northwest-dipping paleoslope approximately normal to the study transect; this is likely a transition from the Kope environment into the Sebree Trough, a narrow basin with poorly understood morphology. A change from limestone-rich to limestone-poor facies, accompanied by replacement of oxic by dysoxic fauna, takes place over a maximum distance of 40 km between two localities along the transect. This represents improved constraint on the Kope–Sebree Trough boundary.