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We document an aspect of the marine paleoecology at Langebaanweg, a site that has produced an abundance of vertebrate fossils. Damage to the bone surfaces of cetacean fossils was not pathological as evident on the fossil seals from this site; the current study documents the damage and attempts to provide a parsimonious explanation. Literature reviews identified similar damage described elsewhere to be the result of shark feeding activity. Comparison of this material with Langebaanweg cetacean bones supports the interpretation that the damage resulted from shark teeth. Damage on the various skeletal elements appears to have been inflicted postmortem or, if they were made while the animal was alive, the whales did not survive the attack. Postmortem damage is also supported by the presence of bites on the dorsal, ventral, lateral, and medial surfaces of a pair of dentaries. Bites were inflicted by sharks with serrated teeth, as well as by sharks with unserrated teeth. Potential predators identified from the marks include white (Carcharodon spp.), Zambezi (bull) (Carcharhinus leucas), tiger (Galeocerdo sp.) and mako (Isurus sp.) sharks.
The recent discovery of crustacean body parts among small carbonaceous fossils (SCFs) has expanded the known range of Cambrian arthropods to include comparatively derived taxa, including copepods. However, the potential for SCFs to reveal larger-scale patterns in Cambrian crustacean evolution has been unclear, because of the small number of known occurrences. Previously, Cambrian copepods were represented solely by isolated mandibles (jaws) from the Deadwood Formation of Saskatchewan, Canada (middle to late Cambrian; = Series 3 to Furongian). Herein we report a second occurrence of Cambrian copepod mandibles, of closely comparable morphology, from the approximately coeval Nolichucky Shale of Tennessee, United States. The Nolichucky specimens were recovered using standard palynological processing, whereas the larger and more articulated Deadwood specimens were recovered using a low-manipulation procedure designed for SCFs. The two datasets represent largely distinct but complementary views onto a taphonomic continuum. In general, larger and more delicate crustacean SCFs reveal phylogenetically and ecologically informative characters, but are likely to be restricted in space and time, and are often low in abundance. In contrast, robust fragments of the same body parts are more likely to be preserved and recovered, but may be unidentifiable in the absence of SCFs. Therefore, conventionally recovered palynomorphs can expand the utility of SCFs to offer a higher-fidelity account of broad-scale evolutionary patterns.
The hydrodynamic behaviors of isolated dinosaur bones have been largely overlooked in the paleontological literature. Investigations into the hydrodynamic properties of dinosaur remains with unique taphonomic signatures, such as pachycephalosaurid frontoparietal domes, have the potential to aid in the interpretation of preservation for skeletal elements for which modern analogues are not available. For this study, a series of transport experiments were conducted to assess the entrainment velocities and settling orientations of a collection of pachycephalosaurid specimens. Casts of four pachycephalosaurid frontoparietal domes and skulls were composed of a urethane resin with a comparable average density to compact and cancellous bone, and placed in a flume with manual velocity control. Data were recorded for competent velocity, transport distance, and settling orientations upon resting and burial of specimens for 35 trials per cast. Though specimens vary considerably in mass, the results suggest specimen shape has a greater influence on transport and hydrodynamic behavior than size; significantly lower velocities are required to transport complete skulls than isolated domes. Resting and burial orientations of specimens vary significantly for domes and complete skulls. The highly variable transport velocities and settling orientations of pachycephalosaurid crania offer insight into pachycephalosaurid taphonomy and illustrate the importance of future taphonomic studies on large fossil vertebrate remains.
The Builth Inlier of central Wales exposes a highly fossiliferous Middle to Late Ordovician (Darriwilian to basal Sandbian) siliciclastic succession in a volcanic, back-arc basin setting. Articulated echinoderm faunas are preserved in a range of paleoenvironments, together with widespread, dissociated ossicles. These have enabled a reconstruction of the distributions of echinoderm groups across a range of noncarbonate facies. The oldest echinoderm assemblages are from sandstone and siltstone deposits, and have yielded only the crinoid Iocrinus pauli and rare asteroids. The most diverse echinoderm assemblages are from a nearshore siliciclastic facies at Llandegley Rocks and equivalent sites. These are dominated by crinoids, together with rare asteroids, caryocystitid rhombiferans, echinozoans, and possible mitrate stylophorans. Deeper-water environments were dominated by the mitrate stylophoran Anatifopsis, associated with variable numbers of holothurians, cornutes, solutans, and rare cystoids (rhombiferans and undetermined blastozoans). The ecological distribution of echinoderms in the area can be summarized as follows: (1) high-diversity faunas in the shallowest environments, composed primarily of large crinoids, with asterozoans and other groups; (2) low-diversity faunas in intermediate water depths, with crinoids (one species) and asterozoans; (3) moderately diverse faunas in deep-water communities with generally small taxa, dominated by stylophorans. These results agree with previous interpretations of environmental preferences among the different groups of echinoderms, but also indicate a separation of dominantly Cambrian-type classes in offshore sediments and Ordovician-type taxa in shallow water. Based on assessments of functional morphology and previously published data, the environmental distributions of these taxa are likely to have been controlled by a complex of factors including sediment type, flow regime, nutrient availability, and temperature. Shallow-water siliciclastic settings may have been crucial environments for echinoderm diversification during the Great Ordovician Biodiversification Event.
Carbonate concretions (N = 18) from the Middle Devonian Hamilton Group were studied using CT X-ray imaging and with computerized 3-D reconstructions. Pyritized burrows and/or body fossils appear causally related to these concretions. When pyritization was noted on the outside of the specimen (N = 15), corresponding networks of pyritized full relief burrow traces could be demonstrated internally. Even when not noted externally, some evidence of pyritic, full relief burrows was noted in all specimens. Because of pyrite opacity, and density contrasts between the limestone concretions and pyrite, these burrows can be tracked through serpentine pathways using 3-D techniques. A brachiopod at the nucleus of one concretion displays X-ray evidence of a possible three-dimensional pedicle preserved in pyrite. This would then be one of the few known pedicles preserved in an articulate brachiopod in the fossil record. Halo formation around the shell edge suggests decaying visceral organic tissue as a probable source of a microbial biofilm, which, in turn, could have served as the nucleus of the concretion. A sequential mechanism is proposed in which both the mucous of burrowing organisms and the decay of visceral tissue served to localize pyritic crusts and concretions near the site of decay, followed by carbonate concretionary growth as pH increased, and available sulfide and iron decreased further from the decay source. These processes comprise end-members in a diagenetic continuum, based on a gradually changing local microbial and chemical environment. Increased bioturbation in studied concretions compared with surrounding sediment suggests increased residence time within the sulfate reduction zone due to sediment starvation following initial rapid burial. This diagenetic observation is suggested to apply to many other cases of concretion formation.
The brittlestar, Ophionotus victoriae, is abundant in Explorers Cove, offshore Taylor Valley. However its ossicles, composed of high-Mg calcite, have not been reported from Cenozoic cores taken from McMurdo Sound. To identify taphonomic processes we analyzed (1) ossicle dissolution and silhouette area loss during a 2-year in situ experiment in which whole dead brittlestars were suspended above or placed on the sediment-water interface at water depths of 7–25 m; (2) ossicle dissolution in a 27-day, in situ experiment using ossicles freed of soft tissue; (3) porosities of experimental and pristine ossicles; and (4) abundance of ossicles in short cores taken at shallow depths in Explorers Cove. SEM analysis demonstrates significantly higher levels of dissolution in ossicles submerged for two years than in pristine ossicles. Submerged ossicles also had significant breakage reflected in silhouette area loss. During the 27-day experiment, submerged ossicles lost between 0.07 wt% and 1.31 wt%. At the observed rate of dissolution it would take between 6 and 105 years for vertebral ossicles to dissolve completely. Ossicles submerged for two years had a slightly higher mean porosity than pristine ossicles; porosity is controlled by variability in the porous stereom structure as well as dissolution. Results demonstrate that ossicle dissolution starts soon after death and that the stratigraphic record does not accurately reflect the presence and abundance of ophiuroids, thus complicating their use in paleoenvironmental, paleoclimatic, and paleoecologic reconstructions. These results also provide baseline information about CaCO3 skeletal dissolution needed to monitor the ocean acidification that is predicted to affect high-latitude benthic ecosystems within decades.