Reading this. As I understand it, dinosaurs were small beer during the Triassic, outclassed by bigger, more dominant competitors, like pseudosuchians and amphibians. Then Pangea split about 201 million years ago, venting vast amounts of magma and noxious gas, initiating catastrophic climate change and triggering the Tr-J extinction event. Dinosaurs fared better than other families, becoming dominant in the Jurassic. There's no consensus as to why.
It sorta stands to reason that dinosaurs' ascendancy has something to do with their adaptability in response to the Tr-J extinction event. But what, exactly? Did the changes to the climate suit their physiology better? Did the mass deaths of other species simply open niches that dinosaurs were then free to fill? There's a lot of room for speculation, but little definitive evidence on which to eliminate competing theories, AFAIK.
The section on the adaptations that allowed sauropods to reach the upper limits of body mass is pretty fascinating.
@lrhodes bipedalism seems to happen under fairly specific circumstances, like for our own ancestors it evidently saved about a biscuit packet's worth of energy a year in the savannah grasslands which turned out to be a significant leg up, as it were. I can see how in many other circumstances/species it wasn't worth it, particularly with the childbirth complications in mammals.
@ljwrites Ah, live birth vs. egg laying seems like a potentially strong differentiator here! Good call.
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