Stegosaurus: A hug of love and fear of being hurt

Stegosaurus is one of the most well-known dinosaurs, with its upright bone plates, thorny tail, narrow face and walnut-sized brain. This type of dinosaur mainly lived in the Jurassic period and became extinct in the middle of the Cretaceous period. Research suggests that it may be because it could not compete with other herbivorous dinosaurs or its physiological structure could not digest the gradually expanding angiosperms.

Reconstruction of a Stegosaurus | Nobu Tamura / Wikimedia Commons

In addition to the pentagonal bone plates like the Stegosaurus, there are many other different bone plate patterns in this family of dinosaurs, such as some species with lower or rectangular bone plates, etc. Among them, there is a species like the Kentrosaurus, where half of the bone plates on its back have become spines. The discovery of this species has also made scientists rack their brains for how this dinosaur mates.

High-end defensive armor

Kentrosaurus is the most primitive species of Stegosauridae discovered so far. It is also relatively small, only about 4 meters long. This type of dinosaur was discovered by a German team during an expedition in East Africa in the 1910s and was exhibited in Germany. Due to the war between the Allies in World War II, some of its fossils have been lost. It can be said that it is a dinosaur that has experienced many vicissitudes.

Kentrosaurus lived in Ethiopia during the late Jurassic period. Apart from being much smaller than Stegosaurus (which could be over 9 meters long), the biggest difference is that its hindquarters did not have plate-like bone plates, but multiple pairs of spines, while its upper body had plate-like bone plates like Stegosaurus.

Size comparison between Kentrosaurus and humans | PaleoGeekSquared / Wikimedia Commons

Research has shown that in addition to defense, the bone plates of Stegosaurus may have mainly played a role in regulating body temperature and identification. The bone plates on the upper body of Kentrosaurus may also have similar functions, while the multiple pairs of towering spines on the lower body exist mainly for defense.

Modern reconstructions of the tail muscles of the Kentrosaurus and computer simulations also show that this tail must have been a deadly threat to carnivorous dinosaurs. The thorny tail can not only swing widely, but also accelerate to 50 kilometers per hour during continuous swings, making predators afraid and unable to approach.

Computer simulation of a Kentrosaurus swinging its tail | H. Mallison / Palaeontologia Electronica (2011)

High defense is definitely a plus for survival, but if the lower body of a spur-shaped dragon is covered with thorns, there is another problem. That is, how should they mate so as not to accidentally castrate the other party?

Hug with love and fear of being hurt

Before discussing the Kentrosaurus, let's first briefly talk about the mating of dinosaurs in general. In the past, some scholars believed that dinosaurs may not have penises like most birds, but instead transfer sperm through "cloacal kissing". However, from the classification system, we can find that crocodiles and primitive birds have penises, so dinosaurs that are close to these two in classification should also have penises.

In other types of dinosaurs, the male would sit with one foot on the back of the female to mate. In addition to lizards and crocodiles with big tails, this posture can also be used as a reference for elephants, rhinos, etc. Most dinosaurs can mate in this way.

Kentrosaurus at the Humboldt National Museum | Timothy E. Isles / Nihil scimus

However, stegosaurus encountered some problems when using this posture, such as the bone plate being too much of an obstacle. Unless the stegosaurus's genitals were incredibly long, it would not be able to complete this action against the hard and towering bone plates. But assuming that the stegosaurus was really that long, if there was no bone support inside, it would not be able to stand up and mate. No stegosaurus has been found to have such a genital structure, so a more reasonable speculation is that the female stegosaurus lay on the ground, and the male entered from the side, so that mating could be completed using a reasonable range of "whip length".

Reconstruction of the mating posture of a Stegosaurus | Timothy E. Isles / Historical Biology (2009)

In addition to Stegosaurus, other dinosaurs with ornaments on their backs, such as Spinosaurus, can also mate in this position, but this is not so simple for the Kentrosaurus. In this position, the Kentrosaurus still has the risk of stabbing the target or even accidentally castrating the target, so scientists have to try other body position models for simulation. After multiple simulations, scientists currently believe that the Kentrosaurus may have mated in a butt-to-butt position, especially since the forelimbs of stegosaurus are relatively short, and in this position the female can better expose the cloaca.

Still exploring in the fog

All of the above are just speculations, which only represent that this position is feasible in terms of physiological structure, but it does not guarantee that dinosaurs must have used this position. The mating patterns of dinosaurs are still almost mysterious, and the corresponding behavioral evidence and physiological structure are difficult to preserve as fossils.

An article published in Scientific Reports in 2016 introduced a strange fossil relic: the dinosaur left behind huge claw scratches, and no traces of eggshells or small dinosaurs were found around, indicating that the pits were not dug for nesting, but may be their courtship performance | Martin G. Lockley / Scientific Reports (2016)

However, with the progress of more fossils and more sophisticated technology, our understanding of the reproductive physiological structure of dinosaurs is constantly improving. For example, trace fossils show that some theropod dinosaurs may have performed courtship dances like modern birds; the dinosaur eggs in the belly of the Oviraptor prove that both oviducts of dinosaurs can lay eggs, but the output is not much each time, etc. Perhaps one day in the future, we will find the preservation of dinosaur genitals in a special stratigraphic environment, or there will be more precise scientific and technological testing methods. These advances may confirm the above hypothesis and may also greatly change people's views on the "private life" of dinosaurs.

This article comes from the Species Calendar, welcome to forward