As for the extinction of the dinosaurs the only solid fact is that no trace of dinosaur has been found after the Cretaceous. This calls for ideas of their sudden disappearance, and a great numbers of theories have been proposed, many of which with a preference for the dramatic.
It should be emphasise, however, that there is no reason to think that the dinosaurs disappeared suddenly. And there is neither any reason to think that they disappeared because they all died! All animals die, but extinction happens because lesser new are born than die.
The dinosaurs were a very great success and the superiors of their time with no competition from other vertebrates. The mammals, which did exist during the entire dinosaurian period, were small nocturnal animals, which played only little or no role to the dinosaurs.
At the beginning of the Triassic various other groups of reptiles, which had survived the great extinction, took their place in the ecological system of the Mesozoic. Those were the diapside reptiles, which evolved into the quadrupedal, sprawling lizards, and the herbivore rhynchosaurs, but the former stayed small, and the latter were slow, clumsy animals, which died out during the Mesozoic. The birds arose during the reign of the dinosaurs, and also did the flying reptiles, the pterosaurs, but none of these met the dinosaurs with any kind of competition, neither did the amphibian archosaurs, phytosaurs and crocodiles, and nor the various species of sea-living reptiles, the ichthyosaurs and the plesiosaurs. From the Middle Triassic the stage was entirely set for the dinosaurs, and they constituted almost exclusively an eco-system of their own.
This system was based on the tall plant-eaters, the sauropods, the various ornitischians, and eventually on the bird-like, plant-eating ornithomimians. These plant-eaters drifted in hosts over the...