A dinosaur-bearing bonebed (Rose Quarry) from the uppermost Cretaceous (Maastrichtian) Lance Formation has yielded abundant, yet fragmentary, disarticulated, and disassociated bones and teeth of dinosaurs, turtles, crocodilians, and fish contained within a channelized sandstone unit along with large mud clasts. The vertebrate fossils of Rose Quarry possess varying abrasion states, tooth traces, and trampling marks, suggesting a complicated taphonomic history. To independently test hypotheses about the genesis of the assemblage, Rose Quarry bone samples were sent to members of our team who conducted “blind” analyses of their trace element signatures without knowledge of the physical taphonomic attributes of each specimen. The independent analyses of the chemical and physical taphonomic signatures both support a mixed, attritional bone concentration. Based on our cumulative data, we present a depositional model for the Rose Quarry bonebed in which a flooding event mixed bones already present in the channel or from an older bonebed with bones from the floodplain that had been scavenged, trampled, and broken. Our study demonstrates that striking variability is possible among fluvial bonebeds, and that such variability is influenced by pre-burial and post-burial factors, as well as depositional subenvironments and burial mechanisms. Additionally, we demonstrate that physical and chemical taphonomic analyses can independently confirm the taphonomic history of a bonebed.

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.

This is a neoichnologic study of Microcavia australis (Rodentia: Caviidae) burrow systems from two environments of the semiarid region of central Argentina, with the main purpose of contributing to the interpretation of fossil tetrapod burrows. We compared three burrow systems from the Monte and three from the Espinal biogeographic provinces to discern which burrow system features vary with environmental parameters (soil texture, climatic conditions, and vegetation type) and identify the distinctive ichnologic features of M. australis burrow systems. Burrow systems from the Monte occur in nebkhas with sparse xerophytic, psammophilic, and halophilic shrubs in sandy and loose soils. In the Espinal province the burrows appear in Prosopis caldenia forest, with shrubs and herbs in silty and harder soils. The Monte burrow systems comprise an intricate pattern with two levels, closed circuits, and larger tortuosity and fractal dimension. The burrow systems from the Espinal display an L-shaped or linear pattern with a single level and commonly lack closed circuits. The average ratio of total chamber volume to tunnel volume and the tunnel diameter is significantly larger in the Monte systems, which is interpreted as a reflection of larger colony size and individuals having larger body mass. Primary surface ornamentation (sets of claw traces related to producer digging) is better developed in the Espinal burrow systems, and secondary surface ornamentation (herein interpreted as arthropod burrows) dominated in the Monte systems. We propose that the distinctive features of M. australis burrow systems can be used as a model to recognize fossil burrows of colonial and fossorial herbivorous rodents that construct a permanent burrow structure with open entrances in semiarid settings. A set of ichnotaxobases for fossil vertebrate burrows is also suggested.