By Andrea Capcap | UTS Staff Writer | SQ Online (2014-15)
Sex is a natural part of life, an ancient affair that’s dated back billions of years. This primal necessity has fascinated many people across time, including Sigmund Freud and E.L. James, and while this fascination is usually centered on human intercourse, copulation in other life forms has also been a prevalent topic throughout scientific history. While most people are probably not rushing to get the latest copy of Fifty Shades of Dinosaurs, understanding how these majestic ancient creatures reproduced can give paleontologists insight to dinosaurs’ behaviors and lifestyles. Much of what scientists know about dinosaur reproduction is based on behaviors of modern-day animals, but there have been significant fossil evidence that can give clues to suggest how dinosaurs lived. For example, in 2011, a pair of oviraptors found buried next to each other in the Gobi Desert, nicknamed “Romeo and Juliet,” was suspected be a mating pair, and further analysis gave strong evidence about possible mating rituals.
Most dinosaur behavioral patterns are theories based on the behaviors of their closest living relatives. In the case of Romeo and Juliet, their closest descendants would be the modern-day bird. For many birds, a flamboyant feather display is one of the methods in a mating ritual. According to the fossil evidence, as analyzed by Scott Persons and his colleagues at the University of Alberta, oviraptors had structural features that supported a courting ritual that involved a flashy display. One of the clues that had alerted Persons to this possible behavior was that oviraptors were suspected to have large tail feathers, but were land-bound creatures. If not used for flight, what were they used for? Persons and his team suspected that much like peacocks and turkeys, the oviraptors used their feathers for courtship displays. In a 2013 paper published in Acta Paleontologica Polonica, Persons found that the fossil’s vertebral patterns supported a highly flexible and highly muscular tail. In other words, the oviraptor may have literally shaken its tail feathers in order to attract mates. Another paper by the same group of researchers, published in March 2015, confirmed that these structural features were sexually dimorphic. Like their modern-day descendants, these flashy displays were a male characteristic. Romeo and Juliet were, indeed, a heterosexual mating pair, and the first to be unearthed.
Plumage may not be the only mating call for dinosaurs. There are also many researchers who believe that horns, crests, and other “exaggerated” features were involved in sexual selection. Much like how antlers on a male deer are used to attract female mates and fight off other males, Triceratops’ horns, Dilophosaurus’ crests, or even Stegosaurus’ spikes could have possibly been used in the same way. Despite the fact these dinosaurs are not ancestors of the modern-day deer, the nature of sexual selection is a fundamental part of biology and is universally intrinsic, regardless of clade. (Nevertheless, there is still much debate over the actual function of these structures—another popular theory among scientists is that they were used for species recognition.)
So what happens after Romeo gets his Juliet? Because soft tissue very rarely gets preserved in the fossil, not much is known about the what’s and how’s of dinosaur intercourse. Determining the sex of the organism is already a problematic task, as sexual dimorphism in structure can be difficult to establish and, unless a pregnant skeleton was found, it can require a lot of time and analysis. Yet again, scientists looked at dinosaurs’ closest living relatives—birds and crocodilians—for clues. They noticed that these two groups have cloaca, the common excretory opening for the reproductive, urinary, and gastrointestinal tracts in these animals. This shared feature may have been an ancestral structure that was also present in dinosaurs. Some male bird and crocodilian species also have penises, which indicate that a phallic structure may have also been present. As with many animals, structures within a clade can vary significantly, and different species of dinosaurs may have different combinations of crocodilian and avian-like reproductive features.
Scientists surmise that intercourse may have occurred via the cloaca, and the male (with or without a penis) may have had to mount his partner from behind in order for their cloacae to come into contact with each other. With the size of these creatures, this may have been the most feasible position. Talk about earth-moving sex!
Persons, W., Funston, G., Currie, P., & Norell, M. (2015). A possible instance of sexual dimorphism in the tails of two oviraptorosaur dinosaurs. Scientific Reports. Retrieved from http://www.nature.com/srep/2015/150328/srep09472/full/srep09472.html
‘Romeo and Juliet’ fossils offer insight into dinosaur romance. (2015, April 1). Retrieved from http://uofa.ualberta.ca/news-and-events/newsarticles/2015/april/romeo-and-juliet-fossils-offer-new-insights-into-the-sex-and-romance-of-dinosaurs
Persons, W., Currie, P., & Norell, M. (2013). Oviraptorosaur tail forms and functions. Acta Palaeontologica Polonica, 59(3), 553-567.