Theropod courtship: large scale physical evidence of display arenas and avian-like scrape ceremony behaviour by Cretaceous dinosaurs

Relationships between non-avian theropod dinosaurs and extant and fossil birds are a major focus of current paleobiological research. Despite extensive phylogenetic and morphological support, behavioural evidence is mostly ambiguous and does not usually fossilize. Thus, inferences that dinosaurs, especially theropods displayed behaviour analogous to modern birds are intriguing but speculative. Here we present extensive and geographically widespread physical evidence of substrate scraping behavior by large theropods considered as compelling evidence of "display arenas" or leks, and consistent with "nest scrape display" behaviour among many extant ground-nesting birds. Large scrapes, up to 2 m in diameter, occur abundantly at several Cretaceous sites in Colorado. They constitute a previously unknown category of large dinosaurian trace fossil, inferred to fill gaps in our understanding of early phases in the breeding cycle of theropods. The trace makers were probably lekking species that were seasonally active at large display arena sites. Such scrapes indicate stereotypical avian behaviour hitherto unknown among Cretaceous theropods, and most likely associated with terrirorial activity in the breeding season. The scrapes most probably occur near nesting colonies, as yet unknown or no longer preserved in the immediate study areas. Thus, they provide clues to paleoenvironments where such nesting sites occurred

LA-ICP-MS analysis of rare earth elements in marine reptile bones from the Middle Triassic bonebed (Upper Silesia, S Poland): Impact of long-lasting diagenesis, and factors controlling the uptake

The rare earth elements (REE) contained in fossil bones are widely used for provenance and palaeoenvironmental studies. Earlier works suggested that the REE uptake is limited to early diagenesis, but more recent research provided evidence of long-term open-system diffusion in fossil bones. We analysed thin-walled reptile bones, all collected from the same Middle Triassic (similar to 245 Ma) marine bonebed, comprising vertebrate remains of likely different ages, to check the influence of the long-term diagenesis on the concentrations of REE, in terms of impact of pore water; the upper parts of the bones are contained in a low-permeability crinoidal limestone, whereas their lower parts have been affected by diagenetic fluids for a long time. We measured REE and other trace element contents in 29 bones using LA-ICP-MS (totally 660 spots in 45 depth profiles). Neither the absolute concentrations of the REE and the REE intra-bone PAAS-normalised patterns, nor the inter-element ratios and the La, Ce and Eu anomalies appear useful to distinguish between the likely older and younger bones in the bonebed. The MREEN enrichment combined with the flat intra-bone distributions of the REE lead to conclusion that REE fractionation and substitution for Ca were the most important processes responsible for the selective uptake. The low-permeability host rock and diagenetic fluids had a significant impact on the trace element uptake and their intra-bone distribution patterns. The lower parts of the bones that likely had a long-lasting contact with the diagenetic fluids reveal a relative enrichment in the REE and their easier diffusion into the bone centres. The ability of fossil bones to incorporate trace elements over a long time-span strongly limits the usage of particularly the older samples for provenance and palaeoenvironmental reconstructions. Additionally, the presented new analyses fill the gap between the available databases of trace element concentrations in fossil bones with regard to Middle Triassic samples. (C) 2013 Elsevier B.V. All rights reserved