The grooves were likely made by male meat-eating theropod dinosaurs, said Martin Lockley of the University of Colorado Denver, CBC News reports.
These dinosaurs appeared to have gathered in groups and “went crazy scraping” with their sharply-clawed three-toed feet in the hopes of attracting mates, Lockley said.
The amped-up dinos were medium-sized as far as theropods go, looking rather like a smaller-sized Tyrannosaurus rex, and footprints near the fossilized grooves suggest that these guys were up to about 16 feet (four meters) long from snout to tail. The grooves they etched were about six feet (1.8 meters) long.
The scrapes were scattered across four different Cretaceous sites in Colorado, Live Science reports. The study’s authors described the site locations as “spectacular” and noted the area is studded with scores of dinosaur trackways, which are lines of footprints made by the same animal. The study was published Thursday in the journal Scientific Reports.
Lockley, an emeritus professor of geology at the university and a co-author of the study, told Live Science that the scrape marks weren’t like anything the scientists had seen before. When they first discovered the scrapes, the prints were partially covered with sand, so the researchers began the painstaking process of cleaning them off to get a better look. Right away, Lockley said, they knew there was something different about the prints. As they worked, more and more scrape traces emerged, until eventually the researchers revealed about 60 of them at one of the sites.
The scientists soon realized that the scrapes were connected to the dinos who marched through the area, making the tracks.
“We were calling them ‘digging dinosaur’ traces,” Lockley said. “They were obviously made by the feet of dinosaurs, because we could see the claw marks. We could see two sides, a left and a right trough, with a ridge in the middle,” he said.
The scrapes are quite similar to a behavior that modern birds, especially those who build nests on the ground, practice — a behavior that’s called a ‘nest scrape display’ or ‘scrape ceremony,’ according to a press release from the university. In these instances, males show off to potential mates by excavating pseudo nests in an effort to show that they can be good providers.
This YouTube video shows one such bird, a killdeer (Charadrius vociferus), engaging in a scrape ceremony.
“These are the first sites with evidence of dinosaur mating display rituals ever discovered, and the first physical evidence of courtship behavior, Lockley said. “These huge scrape displays fill in a missing gap in our understanding of dinosaur behavior.”
The team created 3D images of the scrapes, along with a latex mold and fiberglass replica, IFLScience reports. Researchers made their best educated guess and based the reconstruction on Acrocanthosaurus, Lockley said.
The scrapes especially resemble those made Atlantic puffins during breeding season and the shallow scratches ostriches make. These marks, made in the display arenas (known as leks) weren’t made because the dinosaurs were searching for food, water, or shelter. And, based on the numerous sizes and depths of the scrapes, it’s likely that different species of theropods used these sites while the breeding season was in full swing — most likely in the springtime. It’s also thought that the nests were established somewhere nearby.
The subject of dinosaur sex has always been a bit tricky for paleontologists, BuzzFeed notes. This is due, in part. to the fact that it was considered a bit taboo, and evidence was, well…lacking. No fossils have been found showing dinosaurs enjoying their last moments of coital bliss together. And even well-preserved fossils don’t show reproductive organs of these prehistoric creatures. Even so, scientists are slowing piecing the mating puzzle together by studying birds and crocodiles, which are, after all, the dinos closest surviving relatives. (Of course, as many paleontologists will tell you, there is lots of evidence to suggest that birds are theropod dinosaurs).
Birds and crocodiles have “cloacas,” so it’s quite possible that dinosaurs did as well. A cloaca is an opening which deals with the urinary, reproductive, and intestinal tracts. Males of many of the earliest bird species had a penis that emerged from the cloaca to deliver sperm during sex. So there’s a good likelihood dinosaurs were similarly equipped.
So, now paleontologists have gained a better understanding of how dinosaurs got jiggy with it.
However, I still wonder: How in the heck did a spiky creature like the stegosaur Kentrosaurus have sex?
