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Paleoecological reconstruction relies on accurately determining the taphonomic origin of fossil deposits. Predation is a common mechanism by which skeletal remains become concentrated over time, leading to the formation of modern and fossil prey death assemblages. Skeletal element representation and breakage patterns within such death assemblages can be used to infer the identity of the responsible predator. However, assemblage-level metrics cannot be used to infer if a single fossil specimen is predator-derived. Microscopic digestive etching on individual bones can also indicate past predation events because acidic gastric fluids create distinctive micrometer-scale fissures in cortical bone. Here we establish a quantitative approach to predator identification from small mammal prey remains using microscopic digestive damage patterns. To do this, we collected mandibles from rodents digested by 13 predator species from local wildlife rehabilitation centers, and imaged them using an FEI Quanta 200 SEM. Results indicate that bones exposed to gastric fluids show clear digestive fissures, and that owl-digested specimens can be readily distinguished from specimens that were digested by diurnal raptors and mammalian carnivores. Specifically, owl-digested specimens are characterized by a high density of small and short digestive fissures. Within the owls, digestive fissure patterns appear to scale with owl body size. Finally, we used linear discriminant analysis to build a classification scheme from our modern data and applied it to Holocene mouse fossils from Two Ledges Chamber, Nevada. We found that the fossil specimens display the digestive fingerprints of owls. Quantification of microscopic digestive fissures thus offers a promising new approach for elucidating the taphonomic history of individual fossil specimens.
Broad-scale latitudinal morphological trends in gastropods along the southwestern Atlantic coast are scant, since the majority of studies have focused on local scales. Here, we evaluate biogeographic shell shape variation in the marine gastropod Trophon geversianus across most of its distributional range, covering 14 degrees of latitude. Samples come from death assemblages which have the potential to unveil biogeographic patterns along spatio-temporal scales and are not affected by short-term volatility in comparison with living assemblages. We performed morphometric analyses on shells from death assemblages, and compared shape variation between mid-Holocene and modern shells from one southern site. Multivariate analyses identified two morphotypes matching the biogeographic regions of the Argentine Sea that segregates a warm-temperate from a cold-temperate zone. The Magellan province morphotype is characterized by a larger shell, lower spire height, and higher aperture length than the Argentinean province morphotype. This change in shell shape is significantly correlated to sea surface temperature, even after accounting for spatial autocorrelation, which could be indirectly influencing intraspecific morphoclines via shifts in growth rates. On the other side, shell size and shape variations were also detected (size increase over recent geological time) between mid-Holocene and modern specimens at the Beagle Channel, which could be attributed to paleoenvironmental changes and to shifts in predator-prey relationships. Our study illustrates the usefulness of death assemblages for revealing large-scale patterns of shell-shape variability in mollusk species, and highlights the spatial coincidence of intraspecific morphological differentiation with the transition zone between biogeographic provinces of the Argentine Sea.
Regeneration of portions of the crinoid endoskeleton following loss to predation attempts or autotomy is a well-known phenomenon. To date, however, most effort has focused on patterns, frequencies, and evidence of regeneration of arms and portions of the calyx, with few reports of unusual or significant regeneration-related features preserved in isolated ossicles. Here we describe brachial spines belonging to undetermined pirasocrinid (cladid) crinoids from the Upper Pennsylvanian Ames Member of the Glenshaw Formation of east-central Ohio that display evidence for multiple episodes of breakage and regeneration. As evidenced by major size discontinuities along the length of single spines, some specimens regenerated at least two times during the lifespan of the individual; such a pattern of repeated regeneration of a single skeletal element has not previously been documented. Given the position of these spines on the elevated crown of a moderately long-stemmed crinoid, frequent snipping by predatory fishes seems the most likely interpretation for the observed pattern. The repeatedly regenerated specimens occur in an assemblage displaying an unusually high regeneration frequency among pirasocrinid brachial spines, with over 30% of spines displaying at least one plane of regeneration. Paradoxically, pirasocrinids are unfavorable as prey items relative to other organisms and co-occurring crinoids; hence, it is most likely that associated biota (e.g., commensals, parasites) were the true targets of predators. This assemblage supports the interpretation that the development of extreme spinosity in pirasocrinids was largely driven by predation. However, this morphological pattern may largely represent an evolutionary strategy rooted in minimizing collateral damage incurred by predation on other organisms rather than direct predation on the crinoids themselves.
We here describe the first partial cranium of Hyaenodon leptorhynchus, the type species of the taxonomically diverse and widely distributed hypercarnivorous genus Hyaenodon (Hyaenodonta). The cranium is from the Séon Saint-André deposits (Marseille, France; Chattian, MP26). It is preserved in a dense red marl matrix that obscures key morphological features. CT-scans were used to reconstruct the specimen. The morphology of the cranium reinforces the homogeneity previously observed in Hyaenodon despite its specific diversity. The fossil represents a juvenile: it preserves its deciduous canines and the P3 is almost fully erupted. This pattern of delayed canine eruption is a trait shared among North American and European Hyaenodon. This discovery is the third occurrence of this species in the early Chattian: indeed, over a period of 5 My (from MP24 to MP27), only two occurrences (Rigal-Jouet and Saint-Martin de Casselvi, MP25) have been reported. Based on body mass and the general Hyaenodon body plan, we confidently identify H. leptorhynchus as a cursorial hypercarnivorous predator, hunting prey such as small artiodactyls. In order to understand the evolution of the European carnivorous faunas, we compared taxonomic diversity and the evolution of body mass in Hyaenodon and amphicyonids: this reveals stasis in Hyaenodon through the late Eocene and Oligocene, while amphicyonids show an extensive ecological diversification, especially during the Chattian.