The Changing Fortunes of Extinction
Everyone knows that non-avian dinosaurs are extinct. This catastrophe for the dinosaurs led, over many millennia, to the mammalian dominance that has persisted for the past 66 million years. While many people are aware that mammals took their shot when the opportunity was given to them, it is uncommon knowledge that dinosaurs were given the same chance almost 150 million years earlier.
The earliest dinosaurs appeared during the Triassic period, alongside a wide range of other animals–crocodilians, proto-mammals, large amphibians, and other enormous creatures. The first dinosaurs were small, fleet-footed runners. They diversified in the late Triassic, and then nature gave them a platform.
An extinction event at the end of the Triassic, 201 million years ago, created a vacuum in the terrestrial ecosystems that dinosaurs seized. It was this mass dying that led to the giant Jurassic dinosaurs that would follow. With less competition, the dinosaurs spread across the globe and assumed a bewildering variety of forms. It was extinction that allowed dinosaur dominance.
No clear-cut reason for this extinction event has been identified, but the usual culprits–asteroid impact, sudden climate change, violent volcanic eruptions–have all been debated.
The Cretaceous extinction event eliminated the last of the non-avian dinosaurs, but surely the most successful group of terrestrial vertebrates in the planet’s history would have understood the value of taking an opportunity when it arises. There is never any guarantee that extinction will stay its hand.