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The Alvarez hypothesis posits that the mass extinction of the dinosaurs and many other living things was caused by the impact of a large asteroid on the Earth sixty-five million years ago, called the Cretaceous–Paleogene extinction event.
While there, he explains his story to Bulma: a thousand years ago, an evil race of alien magicians, the Kashvaar, who at sometime proclaimed themselves as the Superior race and set out to destroy all life different to their own in the universe by awakening an ancient monster known as Hirudegarn.
An opposite view is that humankind is Gaia's immune system itself, perhaps evolved to avert future catastrophes such as the Permian and Cretaceous mass extinctions of species.
Gravisauria split off in the Early Jurassic, around the Pliensbachian and Toarcian, 183 million years ago, and Aquesbi thought that this was part of a much larger revolution in the fauna, which includes the disappearance of Prosauropoda, Coelophysoidea and basal Thyreophora, which they attributed to a worldwide mass extinction.
Schindewolf was also the first to suggest, in 1950, that mass extinctions might have been caused by extraterrestrial impacts or nearby supernova.
While other groups of crinoids flourished during the Permian, bourgueticrinids along with other extant orders did not appear until the Triassic, following a mass extinction event in which nearly all crinoids died out.
Gerta Keller (born 1945) is a paleontologist who contests the Alvarez hypothesis that the Chicxulub caused the mass extinction 66 million years ago.