After analyzing the 75-million-year-old remains of a raptor couple likely killed in sand dune collapse, a Canadian paleontologist has discovered dramatic physical differences between the two, a possible sign of sexual dimorphism in the species, and further evidence that these dinos partook in elaborate mating rituals.

The remarkably well-preserved fossil, which was found in Mongolia's Gobi Desert, was analyzed by University of Alberta Ph.D graduate student Scott Persons. A few years ago, Persons co-authored a study showing that oviraptors, among other dinosaurs, featured large tail feathers that were probably used to attract mates, similar to what peacocks do today. The latest study, which now appears in Nature Scientific Reports, adds significant credence to this suggestion.

The two oviraptors, dubbed Romeo and Juliet, were identical in almost every way (including size and age), but one of the raptors featured a much larger tail with bigger muscle attachments.

"It immediately jumped out at me that the bones in the tails had radically different proportions and radically different shapes," noted Persons in the Edmonton Sun. "My first instinct was not to suspect that this was sexual dimorphism, but to actually think that these were two different species. The thing is, though, the differences are all in the tail."

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He says that the features cannot be attributed to an injury or disease as the differences are simply too extreme. The logical conclusion is that it's truly a sign of sexual dimorphism in oviraptors.

Persons says the newly discovered spearhead shape is an indication that oviraptors had a significant capacity for courtship displays, and it was likely done by the male. The female oviraptor had tail bones that were shorter and simpler, suggesting a diminished or un-evolved capacity for so-called peacocking.

Because it's notoriously difficult to distinguish between male and female dinosaurs, the researchers are working under the assumption that males featured the elaborate display. More work is required for the scientists to be more definitive.

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Read the entire study at Nature Scientific Reports: "A possible instance of sexual dimorphism in the tails of two oviraptorosaur dinosaurs".

Images: University of Alberta/Persons et al./Nature Scientific Reports.

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