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

Abstract

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.

Palaeontology: Scrapes of Dinosaur Courtship

“…Most dinosaur nests were bowlshaped depressions in the ground, Dispatches sometimes with a raised lip and this is quite different to the paired scrapes seen here [5]. Furthermore, the nest scrape displays show no traces of eggshell or tracks from juveniles that might indicate these were linked to nests and distribution of traces is also different to known nesting colonies of these two groups as well.…”

“…Traces can provide exact records of behaviour, although correctly interpreting even simple behaviours can be difficult [3], and ascribing traces to a given species (or even major clade) has its own problems since traces are only very rarely preserved alongside body fossils [4]. Even so, convincing cases can be made for important behaviours based on the trace fossil record such as in a recent study by Lockley et al [5] reporting on a novel trace fossil for Mesozoic dinosaurs. These are 'nest scrape displays' that are known to be produced by a number of living birds but were previously unknown in the dinosaur fossil record.…”

“…The new traces described by Lockely et al [5] are pairs of deep scratches that are up to two metres across made in the ground with the clawed feet of large bipedal dinosaurs (Figure 1). The size of these traces indicates that these were not left by small animals, and the nature of some traces show the outline of large tridactyl feet that clearly point to theropod dinosaurs -the group of primarily carnivorous bipeds that include famous genera such as Tyrannosaurus, Allosaurus and Velociraptor.…”

Focus stacking photogrammetry for micro‐scale roughness reconstruction: a methodological study

“…With the advance of digital cameras, photogrammetry has been successfully applied in both laboratory assessments (Lee and Ahn, 2004;Fujii et al, 2007;Nilsson et al, 2012) and field measurements (Fujii et al, 2007;Haneberg, 2007;Bistacchi et al, 2011;Corradetti et al, 2017a) of fault and fracture wall roughness at different length scales. It has also been recently applied to surface tracking in analogue experiments (Heng et al, 2010;Galland et al, 2016), fold analysis (Vollgger and Cruden, 2016;Corradetti et al, 2017b), fault or fracture spatial analysis (Lato and V€ oge, 2012;Vollgger and Cruden, 2016), stratigraphy (Nieminski and Graham, 2017) and palaeontology (Lockley et al, 2016). Nowadays, thanks to the intensive development of computer technology and digital photography, photogrammetry has become an affordable and popular method of 3D imaging.…”

Triassic pentadactyl tracks from the Los Menucos Group (Río Negro province, Patagonia Argentina): possible constraints on the autopodial posture of Gondwanan trackmakers

“…Tetrapod tracks are valuable fossils which inform us about the anatomy (e.g., Carpenter, 1992), functional adaptations (e.g., Baird, 1980), motion (e.g., Avanzini, Piñuela & García-Ramos, 2011) and ethology (e.g., Lockley et al, 2016) of extinct animals, greatly expanding the potential of information that is often precluded from the body-fossil record. The detailed analysis of tetrapod footprints is therefore significant for integrating and revising data derived from the tetrapod body-fossil record.…”