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The non-avian dinosaurs constituted a huge clade, and adaptations within the clade need not have been ubiquitous among dinosaurs. That is, adaptations are ways in which creatures solve problems having to do with how they make a living and survive in a given environment. So different environments and/or processes within a given environment force species to come up with different living arrangements even within a given clade.

For example, among mammals there are herbivores, carnivores, and omnivores, each adapted to different nutritional regimes tailored for different lifestyles and even anatomical configurations. A tiger does not look like a rabbit, and its preferred food is not what rabbits like and need. And bears differ from both, on both counts.

Okay, how about giving birth to live young vs. laying eggs and tending the nedt, or hatching eggs within the mother's body? In his book The Dinosaur Heresies, Dr. Robert T. Bakker suggests that the big sauropod dinosaurs, such as Apatasaurus and Brachiosaurus, might have given birth to live young rather than laying eggs. Why? Think of just how far to the ground an egg laid by a female of either genus an egg would have had to fall and . . . crunch! So much for that egg -- or any others laid by such mothers. A baby born alive to such a dam would have had a much higher chance of survival than that poor egg, falling as the latter did to the hard, indifferent ground yards below her belly!

So why wouldn't that particular reproductive adaptation have been more widespread among big dinosaurs, even among the carnivores? A careful examination of a fossilized pelvis of a big female dinosaur could tell the tale: A uterus is one big muscle. It has to be, in order to be able to expel junior into the big wide world when it's time for the baby to be born. That means that in cases in which dinosaurs had uteruses and had also produced at least one offspring, there were would be muscle scars at attachment points on the pelvic bones where the uterus was anchored. Consultation with a gynecologist, or a veterinarian who has had plenty of experience with pregnant animals and who has done necropsies on female patients who didn't make it, could help to answer this question. Certainly, looking up information on Spinosaurus and its relatives, big dinosaurs who lived almost entirely in rivers and lakes, makes it clear that these animals had much the same problem that ichthyosaurs did: how to reproduce in an element that had no stable ground on which to lay eggs and was full of predators. The ichthyosaurs solved that by undergoing live birth (viviparousness) in the water itself, the mother ichthyosaur there to protect the baby once it was born, without having to prepare a nest on land. The spinosaurid dinosaurs may have done the same thing.

I have no idea how I could go about proving out this question one way or the other, but I'd love to have a gander at the fossilized pelvises of big dinosaurs with a gynecologist or veterinarian standing by to point out what I'd missed and what it meant -- or, for that matter, what I found and what it meant, when it came to trying to determine whether a given dinosaur laid eggs (ovoviparity), hatched her eggs within her body and then gave birth to them alive (ovoviviparity), or underwent live birth (viviparity). If any of you out there know something about this fascinating question, could you let me know in the comments? Thanks in advance.

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