Dinosaur Sex and Cloacal Kisses
Featured in Hope for the Best by Jodi Taylor
Imagine the Cretaceous period, when dinosaurs roamed the Earth. Now let's delve into dinosaur romance, from their courtship dances to their nesting habits.
Dinosaur Courtship: The Original Dance-Off
Just as modern birds perform elaborate dances to woo potential mates, some dinosaurs had their own moves. Fossilised scrape marks found in numerous sites in Colorado suggest that, much like modern birds, some dinosaurs may have performed nest-making or ground-scraping displays to impress potential mates. These marks, dating back approximately 100 million years, were found in Cretaceous-aged sandstone and are characterised by large, shallow depressions accompanied by elongate scratch marks. The scrapes, some measuring up to 2 metres in length, are irregularly grouped, resembling display arenas similar to those used by certain modern birds during their own mating rituals.
Feathered Flair: Dressing to Impress
Feathers weren't just for flight; they played a significant role in dinosaur courtship. Species like the Oviraptor had impressive plumage, which they likely flaunted during mating displays. Peacocks are an example of this same behaviour today.
Nest Building: Home Sweet Home
When it came to starting a family, dinosaurs were meticulous planners. Many constructed nests in which to lay their eggs, with some species, like the Oviraptor, displaying remarkable dedication by brooding over their clutches to keep them warm. These attentive parents arranged their eggs in circular patterns, which helped share the parents' weight and ensured each egg received equal warmth and protection.
Egg-Laying: A Diverse Affair
Dinosaur eggs came in various shapes and sizes. Recently, the world's smallest dinosaur egg, measuring just 29 millimetres, was discovered in China, and offers insights into the reproductive habits of these ancient creatures. This tiny egg, smaller than a 50p coin, showcases the incredible diversity of dinosaur reproduction. The largest dinosaur eggs ever discovered belong to the oogenus Macroelongatoolithus, with some specimens measuring up to 61 centimetres (2 feet) in length. These elongated eggs, resembling loaves of French bread, have been found in North America and Asia. Notably, a significant find occurred in China's Henan province in 1992.
Massive eggs are also associated with giant oviraptorosaurs, such as Beibeilong sinensis. Studies indicate that Beibeilong laid eggs approximately 40 to 45 centimetres long, weighing over 5 kilograms each. The adult Beibeilong is estimated to have measured about 7.5 metres in length and weighed between 1.5 to 2.5 tonnes.
The Act Itself: Cloacal Kisses
Palaeontologists believe that most dinosaurs likely mated in a similar manner to modern-day reptiles and birds, which are their closest living relatives. This would mean that they engaged in copulation via cloacal contact—a method known as the "cloacal kiss." Like modern birds and reptiles, dinosaurs likely had a cloaca, a multi-purpose opening used for excretion, egg-laying, and reproduction.
Since no fossilised reproductive organs have been found, it is assumed that some male dinosaurs may have had an extendable penis, much like modern crocodiles.
The Challenge of Mating for Large Dinosaurs
The sheer size and bulk of some dinosaurs would have made mating a logistical challenge. For instance, a massive theropod like Tyrannosaurus rex, which stood over 12 metres (40 feet) long and weighed up to 9 tonnes, would have required careful positioning to avoid injury.
Some theories suggest that:
• Large dinosaurs may have used their tails for balance while mounting their partner.
• Some species may have mated side-by-side, like modern reptiles.
• Others, particularly quadrupeds like sauropods, may have reared up on their hind legs to engage in copulation.
Did T. rex Use Its Short Arms for Sexual Tickling?
One of the most debated topics in dinosaur palaeontology is the function of Tyrannosaurus rex’s tiny arms. At around 1 metre (3 feet) long, they seem disproportionately small compared to its massive body. While some researchers believe they were simply vestigial structures, others have proposed a range of possible functions, including helping to grip prey, assist in rising from the ground, or playing a role in mating.
The idea that T. rex used its arms for sexual tickling or courtship has been discussed, though it remains speculative. Some palaeontologists suggest that male T. rex might have used their arms to gently touch or stimulate their mates during courtship or mating, similar to the way some modern reptiles use their limbs for tactile communication. However, other palaeontologists argue that their arms were small, had limited range of motion, and were equipped with strong claws, thus rendering their role in courtship unclear.