Millions of years ago ammonites filled our oceans, with species from a few millimetres across to huge examples over three metres in diameter.
251 million years ago there occurred what is known to scientists as the Permian–Triassic extinction event, or more evocatively as ‘the great dying’. This was the Earth's most comprehensive mass extinction and at a time when the majority of life on this planet existed in the ocean, the event killed over 95% of all marine species, including over 90% of ammonite species. However, in the period following the extinction event, new species evolved, including a wide variety of new ammonites. Diversity returned.
About 205 million years ago, the planet suffered another mass extinction, the Triassic–Jurassic extinction event. In the seas over 90% of ammonite species again became extinct. Once again after the extinction, news species evolved. The extinction left the dinosaurs as the dominant land animals and a huge variety evolved. In the oceans, new ammonite species evolved to fill the gap left by the extinction.
Then about 65 million years ago the planet suffered the Cretaceous–Tertiary extinction event or K-T extinction. About 75% of species became extinct. Although statistically not the most comprehensive extinction event, it is undoubtedly the most famous as it resulted in the end of the dinosaurs. Mammals and birds emerged as the dominant land vertebrates in the age of new life. The K-T extinction event also finished off the ammonites.
As one might expect, considerable scientific research effort has gone into investigating the circumstances giving rise to mass extinction events. In 2008, Nan Crystal Arens and Ian West published Press-pulse: a general theory of mass extinction? This proposed a model which suggests that mass extinctions generally require two types of cause: long-term pressure on the eco-system which they referred to as ‘press’ and a sudden dramatic event or ‘pulse’ at the end of the period of pressure. Their statistical analysis of marine extinction rates suggested that neither long-term pressure alone nor a catastrophe alone was sufficient to cause a significant increase in the extinction rate.
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