Features that paleontologists have long found sexy about dinosaurs were probably sexy to the dinosaurs themselves. Even feather patterns on some dinosaurs, such as the striped tail of the fuzzy dinosaur Sinosauropteryx, hint at visual signals being very important to dinosaurs in terms of socializing and impressing potential mates. The discovery of vast dinosaur display arenas underscores how dinosaurs went to lengths to show off.
The scratches in the ground were originally thought to be failed attempts at making nests. Upon closer examination, however, paleontologist Martin Lockley and colleagues realized that there were multiple such scratch marks in close proximity to each other at multiple fossil sites across Colorado. The marks were made by large theropod dinosaurs, perhaps akin to the giant carnivore Acrocanthosaurus, that gathered in one place to display to each other. Some modern bird species still engage in the same behavior today, avians like puffins coming together in an area called a lek to scratch at the ground. The dinosaurs danced to impress.
“Scrape displays often being as soon as a pair occupies a territory,” Díaz-Martínez says, usually with male birds demonstrating they could ably dig out a nest. The large dinosaurs, around the size of the 30-foot-long Allosaurus, may have scratched at the ground for the same reason, as a sample of the nest they could build. Since the traces were first reported in 2016, paleontologists continue to document additional display arenas where dinosaurs courted each other prior to mating and nesting.
Even with all paleontologists have learned, however, the known case studies apply to specific dinosaur species or groups. In the case of the scrapes, paleontologists have not yet identified the exact species of the dinosaurs who left the ruts behind. But each new find raises new questions about the intimate moments of dinosaur love lives.
More evidence is almost certainly out there, in the rock record. While undoubtedly rare, it might be possible to identify dinosaur mating habits from tracks. “If mating involve positions that left distinctive impressions such as overlapping trackways, claw marks from grasping, or localized deformation to the sediment, these could be preserved under exceptional circumstances,” Díaz-Martínez says. The dancing dinosaur scrapes reveal courtship, but other forms of footsteps, scratches, and other traces would uncover the actual moment of dinosaur mating.