But I won't speculate on these things because I want to do some serious speculation later in this post. Perhaps, as I claim, the mammal's secure reproduction played a part in this increase in evolutionary creativity. Species have different strategies the effectiveness of which depends entirely on their niche. Egg-laying in crocodiles works because, sovereigns in their swampy habitat, they can guard their nest with ferocious efficiency, on their own terms. Egg laying in most snakes is okay because the nest is either guarded by venomous parents, or the eggs are down some slithery hole which only the parent can reach.
Lizards are small and can hide their eggs well.
Turtles make a single stealthy trip to lay their eggs, then they forget them. But dinosaurs, big and parentally invested, had no means of avoiding detection. The only strategy they could resort to was defence of the nest. Derek is very generous in letting me compare two species that didn't ever exist together, i.e, a dinosaur and a precocial mammal, both the same size, herbivorous, and herding. He says the pregnant female is a liability for mammals.