The “Carnian pluvial” period is now attracting more attention:
About 232 million years ago, during a span known as the Carnian age, it rained almost everywhere. After millions of years of dry climates, Earth entered a wet period lasting one million to two million years. Nearly any place where geologists find rocks of that age, there are signs of wet weather. This so-called Carnian pluvial episode coincides with some massive evolutionary shifts.
Perhaps most dramatically, the Carnian pluvial might have overlapped with when a rare group of reptiles — early dinosaurs — evolved into a diverse group and came to dominate land ecosystems. The Carnian could have paved the way for the spectacular dinosaurs that evolved later, including Stegosaurus and Tyrannosaurus.Michael Marshall, “Did a million years of rain jump-start dinosaur evolution?” at Nature
There’s some dispute that there was really that much rain coming back from the Permian extinction – or even rain at all, as opposed to rising seas. But it’s an interesting thesis anyway.
What’s clear is that dinosaurs changed drastically. At the start of the Carnian, they were all small and bipedal. But by the end, the two major groups had emerged. These were the ornithischians, which later included Stegosaurus and Triceratops; and the saurischians, which gave rise to huge, long-necked species such as Brachiosaurus, and theropods such as Tyrannosaurus rex and birds.Michael Marshall, “Did a million years of rain jump-start dinosaur evolution?” at Nature
So something happened. But was it rain? Can rain do all that is needed?
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