In short, the display arena interpretation provides the missing link in a threefold plexus of traces that can be arranged in a coherent time sequence tied to the breeding season: trackmaking-courtship display-nesting.
Although such trace-making activities do not necessarily take place at the same locations, given the stereotypical cycle of breeding behaviours among many extant avians, (congregation, display, copulation, nesting, incubation, etc.), it can be confidently inferred that abundant scrapes indicate that nest sites were established nearby.
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.
However, inferences about phylogenetic relationships based on behaviour are generally more speculative.
Despite extensive phylogenetic and morphological support, behavioural evidence is mostly ambiguous and does not usually fossilize.By implication, these traces, here named Ostenichnus bilobatus, (“bilobed display trace”) were made in the breeding season, probably springtime.Moreover, such lek-like, “display arena” evidence links two ubiquitous classes of trace fossil: locomotion traces (repichnia) and nest sites (calichnia).Thus, scrapes are signatures of paleogeographical significance pointing to preferred paleoenvironmental nesting sites, even as shown here where no other direct physical evidence of nesting is preserved.Four sites with large nest scrape display traces have been identified in the Cretaceous (late Albian-Cenomanian), Dakota Sandstone of Colorado, three in the west, and one in the east of the state.Despite this abundance of footprints, display scrapes represent a previously-unrecognised, entirely new category of vertebrate trace fossil.