Dinosaurs in bed – foreplay

What do dinosaurs getting it on have to do with engineering one might well ask? The answer is: surprisingly, rather a lot actually. In fact, all structures, including living things, are subject to engineering principles. Like all structures, animals too are to a large extent optimized for the stresses and strains of their daily lives, and surprisingly, to a certain extent, because they are living things, their structures can adapt to changing conditions. This is why astronauts, once they get into the microgravity of space for example, start losing bone and muscle mass as their bodies adjust to the changed demands placed upon their bodies by their new gravitational regime.

Source: http://chasmosaurs.blogspot.com/2012_04_01_archive.html
Chasmosaurus doing their thing.

Of course, there are tolerances built in, and overall the bodies and skeletal structures of animals are extremely well adapted to deal with the physical stresses of the environment they evolved to live in. In a way, this is why when engaged in normal physical activity like running and jumping, humans do not need to wear special protection: our legs, skeletons etc. are more or less capable of withstanding the physical shocks of engaging in such behaviours as long as we undertake them under our own steam. Take it up a notch though, and corporeal protection becomes really necessary: we did not evolve to withstand the battering involved in playing ice-hockey or American football, and this is partly why we need to wear special protection when we partake of these kinds of activities.

This is also why bighorn sheep do not need crash helmets thoughmotorcyclists do, and why attaching a howdah (riding platform) to an elephant’s back is really bad for it. It’s all about engineering design, or in this case, bioengineering design.

There are countless other examples of bioengineering out there, but today I would like to write about something rather unusual: dinosaur mating. I’m not referring to all the pre-mating rituals of posturing, bellowing, honking, chestthumping, chasing-away of rivals, gyrating in some kind of mating ‘dance’ and so forth, about which we can for the most part not even speculate meaningfully (apart, that is, from noting that certain features, like long necks, spiny plates, thumb-spike, long, trumpet-like nasal cavities, and the like were probably much involved in these activities, and may even have evolved exclusively as a result of sexual selection pressures). We certainly do know that, like many more familiar animals, dinosaurs too sometimes fought with each other: there are many fossilised skulls with teeth marks on them which were made by the teeth of the same species as the injured animal. Were these injuries imparted during their mating season? We can’t know for certain, but based on how most animals around us (including us I might add) behave today, this certainly does seem like an awfully safe bet.

No, in my next couple of posts, I’m going to write about the heaving and grunting of the actual physical act. When we think of the smaller dinosaurs, velociraptors for example, there seems to be no big problem involved: we can imagine a scenario similar to what animals of a size familiar to us do, without us having to give us special consideration to the likelihood of enormous stresses being placed upon the physiologies of the copulating pair. When we start thinking about massive dinosaurs though, animals the size of apatosaurs (formerly known as brontosaurs) and beyond, things become decidedly more complicated because of their massive and very long bodies.

This needs a little more clarification I think. An animal’s skeleton, organs and musculature evolved not just to support its static weight, but also to support its weight whilst that animal walks, runs, jumps lifts and lowers its neck, and so on. Animals which do not run and jump would not need skeletons proportionately as strong as animals which do run and jump and climb trees and so on. Thus one could make the case that the leg bones of a leopard are proportionately sturdier (given the mass of the animal), than the leg bones of elephants (which neither jump, nor climb trees last time I checked). This observation will be of great significance shortly.In writing about dinosaur sex, let’s first digress a bit and look at how we know about them at all in the first place. All our knowledge of these animals comes from fossils. Unfortunately for us, hard structures (like bones, teeth and even egg-shells) fossilise far more readily than soft structures like hair/feathers, organs and skin, consequently, we do not have any fossils (at least to date) of any dinosaur’s sexual organs (and precious few fossils of their skins and feathers).

When it comes to their behaviours (sexual or otherwise), it’s even more of a problem: With the extremely rare occasion of 2 or more animals fossilised at the moment of their interaction, much of the time, we have to speculate on how they might have behaved when in company, drawing upon our knowledge of current animal behaviour to inform our guesses.Were there 2 sexes of dinosaurs? Well, sexual reproduction began well before dinosaurs evolved, and is a very popular method of reproduction. Although there are unusual variations in some species like some fish which can switch from male to female etc, and whilst there are some other organisms which can reproduce asexually, we have ample evidence that dinosaurs reproduced sexually. To note just two of these bits of evidence: firstly, many other animals prior to dinosaurs, including their direct ancestors, had male and female forms; and secondly, we have evidence of sexual dimorphism in dinosaurs (dimorphism is when the males and the females are of different sizes and shapes, or have different features – quite clearly, not all animals exhibit sexual dimorphism, but many species of birds, fish, and mammals certainly do exhibit this trait, as do many monkeys and apes including us).

Now, for a long time, we did not know how to tell male and female dinosaurs fossils apart, but then Mary Schweitzer discovered that in their fossils there was something which could be used to sex the animals, sometimes: in birds, females draw calcium from their own bones just before laying eggs, as they need it to produce the egg-shells. The source of this calcium is a type of bone tissue called medullary bone, which lines the insides of their leg-bone cavities; Schweitzer found evidence of medullary bone tissue in the fossils of some dinosaurs too, and was thus enabled to conclude that these particular fossils at least belonged to female dinosaurs which were about to lay eggs.

Just to adumbrate this better, remember that when we talk about dinosaurs, we are essentially reconstructing the entire animal from fossilised remains (and at times from incomplete fossilised remains at that). If the fossilremains of let’s say a juvenile or female dinosaur are significantly different from those of a male, we might not even know that they belonged to the same species (as an example, though this is a bit of an extreme case, if you did not know that frogs and tadpoles belonged to the same species, I doubt that you would be able to divine that fact just from looking at their skeletons, fossilised or otherwise – in fact, it’s unlikely you’d be able to do it even if you were simply shown the live animals). By the by, when it comes to dinosaur egg-fossils we have a similar problem: unless the parents are also fossilised on or near the egg-fossils, or unless the egg-fossils contain well-formed embryos, we cannot possibly tell which species of dinosaur those egg-fossils came from.

As I already noted, the reconstruction of animals, the like of which we have never seen, is a delicate and risk-fraught affair, and any palaeontologist worth his / her salt needs to always be willing to reconsider matters and in the face of convincing evidence, to reverse their reconstructions. Caveat emptor one might well say. Though this is not to say that it’s all uncertain and that the creationist folks are right; they’re not because their speculations do not take into account all the facts, and are at best based on a highly selective application of facts, chosen so as to fit their assertions in a totally ex post facto manner.

Maybe, before we go any further though, it might behove us to talk briefly about sexual reproduction from an evolutionary point of view. The good thing about it (aside from the obvious) is that it creates new organisms by mixing genetic material from two different organisms (though from the same, or occasionally from very closely related species – though these hybrids (ligers, mules and the like) tend, generally, to be sterile); that having been said though sometimes the results can be truly impressive.

The evolution of sexual reproduction is currently the subject of much debate, and there are several hypotheses competing with each other to account for it. We do know that it first appeared about 1,200,000,000 years ago, amongst eukaryotes from the Stenian period (which is about one third of the way from us to the beginnings of life on the Earth, which happened about 3,800,000,000 years ago), and we know, since it is the primary mode of reproduction for the vast majority of macroscopic animals (including almost all animals and plants), that it was a big hit once it evolved.

Furthermore, we know that dinosaurs must have had the equipment for internal fertilisation, and that it was a mode of reproduction that they inherited from their ancestors. When the first limbed vertebrates began to creep out of the water and crawl around its edges around 380 to 375,000,000 years ago, they were most certainly already engaging in sexual reproduction, though they were probably not yet using internal fertilisation as the method for getting the sperm to the egg; they were amphibians, and if they were anything like modern amphibians, they would have reproduced in the water, the female laying soft, shell-less eggs in clusters in the water and the males then squirting sperm over them to fertilise them. By about 315,000,000 years ago however, some of these erstwhile amphibians had developed the capability to reproduce away from the water, and were laying eggs encased in a tough outer shell. This meant that the old method of squirting sperm over the eggs would no longer work, and the union of these two had to take place earlier. This was the beginning of internal fertilisation, which took place before the eggs were deposited in a nest. This is a tradition which has been carried on by all the descendants of these early animals, including both dinosaur and us, though not always in the same way: some animals do it not by the actual intromission of a penis, but simply by means of a cloacal kiss.

snake_cloaca

Source: http://herpy.net/gallery/details.php?image_id=9888&sessionid=c7963e015149ee5
7c3642d720b5b433a
A snake cloaca

Cloacina is the Roman goddess of sewers and of sexual intercourse (those kinky Romans), and cloaca, the Latin word for a sewer, is also the term for the multi-function opening which reptiles and birds have, out of which they excrete, lay eggs, and also have sex.

Whilst some reptiles and birds certainly have them, an intromittent organ (like a penis) is not strictly necessary in order for fertilisation to occur, and it is possible that dinosaurs (or at least some of them) ‘did it’ this way. We don’t really know though, and there are many mechanical issues with this. Before I can write about that though, I need to digress again and write about iconographic issues and how they influenced out thinking. However, I notice that this post is now getting rather long, and I’m going to have to put the rest of this off until next time. Sorry to leave you dangling – as it were.

Jothiratnam

Jothi's a guy who's inordinately curious about all manner of things, and has been trying to understand the way the world, in all its myriad facets, works, as well as to convey his understanding of this to all and sundry for most of his life. He has tertiary-level academic qualifications in a variety of different fields ranging from the hard sciences, through the social and behavioural sciences, to the humanities. He's willing to try almost anything at least once, and many things more than once.

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