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Dinosaurs Were into Foreplay, New Study Says

Evidence of "scrape traces" that suggest courtship mating rituals in dinosaurs have been discovered in a 100-million-year-old rock formation in Colorado.
Hold your horses, buddy. Photo via Wikimedia Commons

Even in the Cretaceous Period, oral was key.

Not really, but metaphysically, it could be said that dinosaurs engaged in foreplay. That's the finding, or at least a very sassily editorialized version of it, from a new study published in the journal Scientific Reports last week. Based on a discovery of scrape traces in the Dakota Sandstone of Colorado, an approximately 100 million-year-old rock formation, University of Colorado–Denver paleontologist Martin Shockley and his team were able to do something scientists who study dinosaurs rarely get to: hypothesize about behavior—and sexy behavior, at that.

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"Behavior can be a tricky trait to determine because a lot of behavior doesn't have a great chance of being fossilized," says Lisa Buckley, a co-author on the paper and a paleontologist at the Peace Region Palaeontology Research Centre in British Columbia. "We can get some information on possible behavior from skeletons. How the bones move, how the muscles connect to the bones, and what soft-tissue features are preserved (feathery plumes, skin, etc.) give you a good idea of what was possible, but form doesn't always equal function, or one form might have multiple possible functions."

Faced with these difficulties, paleontologists examine modern animals, their traces, and their motives for leaving the traces they do. They then compare those traces to fossilized ones. "That's our best line of evidence when figuring out the 'Why?' of a trace," says Buckley.

That was the process here. The scrape traces in the Dakota Sandstone consist of scratches that are similar to "pseudo nest-building" traces left by living birds. The first fossilized evidence of its kind, the 60 scrape traces discovered by Shockley and his team suggest dino courtship behavior that would have involved males doing a little dance ritual to get females to agree to make a nest with them. The scratches are up to several feet long and, most significantly, offer evidence of sexual selection in non-avian dinosaurs, something that researchers have not yet been able to discern.

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Look at my wonderful territory-selecting and nest-making prowess: All this could be yours if you will be my mate.

If this doesn't sound like "foreplay" to you, well, I was disappointed, too. But while this might not sound like what you do before getting down to your heteronormative business, Buckley says that's not really a productive way of thinking in evolutionary terms. "It's foreplay in the sense that it allows individuals to communicate the readiness and willingness to move on to the next step: mating," she says.

The study in Scientific Reports notes that these scrape traces could also be remnants of "scrape feeding," when animals scratch around for food in the ground. It's also possible that they are evidence of actual nest building. But Buckley says these hypotheses aren't as compelling as the courtship ritual one. "From what feeding digs and scrapes I've seen from extant wild animals in northeastern British Columbia, those [feeding] digs do not have the claw scrapes preserved—they get stirred around and flattened out by the animal (bear, deer, elk, etc.) extracting the freshly dug roots or invertebrates. Also, the rock in which the [dinosaur] scrapes are preserved is quite barren in terms of other signs of life: There are very few root traces preserved, and no invertebrate burrows in the scrape layer." What's more, Buckley says that scrapes they found don't match fossilized dinosaur nests, which are more circular and bowl-shaped than the long ones in the Dakota Sandstone.

Foreplay of a more familiar type is not uncommon within the animal kingdom. A 2013 study revealed that male fruit bats engaged in cunnilingus to make sex last longer; what's more, the male bats were probably Male Feminist bats, because the oral lasted way, way longer than the penetration: On average, a bat sack sesh would start with about a minute of oral, 15 seconds of intercourse, and then two-and-a-half minutes of more oral. Hyenas and notoriously sexual bonobos have also been known to tongue their lovers. (Many species self-fellate as well, for the interesting evolutionary reason that it decreases their likelihood of contracting STDs after intercourse.)

So how did dinosaurs, already pretty ridiculous-looking, behave when they were getting ready to do it? Female dinosaurs may not have been as lucky as fruit bats, though they were probably privy to an interesting display. "Looking at extant birds, like plovers, the male finds a suitable area in which to display, crouches down, and uses his feet to scratch and kick the sediment into a shallow, elongated depression," Buckley explains. "He's both marking his territory and showing the female, Look at my wonderful territory-selecting and nest-making prowess: All this could be yours if you will be my mate. A male will make multiple scrapes before a female will choose him—many scrapes are rejected."