Ichthyosaurs - shark-like marine¹ reptiles³ from the time of dinosaurs⁴ - were driven to extinction⁵ by intense climate change and their own failure to evolve quickly enough, according to new research by an international team of scientists. The study provides an explanation for one of the longest-standing enigmas⁶ in palaeobiology: how and why ichthyosaurs died out. Unlike other marine reptile² groups, ichthyosaurs disappeared tens of millions of years before the end-Cretaceous extinction (65 million years ago) that marked the end for dinosaurs and the beginning of the age of mammals.

 

The research is published in the journal Nature Communications.

 

First author Dr Valentin Fischer, of the University of Liège, Belgium, and the University of Oxford⁷, UK, said: 'We analysed the extinction of this crucial marine group thoroughly⁸ for the first time. We compared the diversity of ichthyosaurs with the geological record of global change, emphasising the dynamics⁹ of these datasets.

 

'Ichthyosaurs were actually well diversified¹⁰ during the last chapter of their reign¹¹, with several species, body shapes and ecological¹² niches¹³ present. However, their evolution was much slower than earlier in their history. Additionally, they were seemingly negatively affected¹⁴ by the profound global changes going on during the Cretaceous, as their extinction rate correlates with environmental volatility¹⁵.'

 

Causes of extinctions - including the demise¹⁶ of the ichthyosaurs, or 'sea dragons' - have often remained elusive¹⁷ and conjectural¹⁸, particularly when they cannot be linked to an obvious geological or geochemical event such as a large meteorite¹⁹ or massive volcanic²⁰ eruption²¹. Ichthyosaurs were regarded as undiversified for a prolonged period before their extinction, and their dying out has previously²² been linked to minor²³ events including increased competition with other marine predators²⁴ and a decline in their assumed principal source of food.

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