Marine dinosaurs evolved extremely quickly, study finds

Hundreds of millions of years ago, marine reptiles like the ichthyosaurs and plesiosaurs ruled the seas—but researchers were never quite sure about their origins, or their rise to dominance. Now, research published from paleobiologists from the University of Bristol has shed some light on their mysterious past.

As told in their paper in Paleobiology, the scientists have uncovered evidence that during the Mesozoic– an era about 252 to 66 million years ago—these predators suddenly burst onto the scene, instead of a slow evolution into their environment.

“We show that when marine reptiles first entered the oceans in the Triassic period, they rapidly became very diverse and had many morphological adaptations related to feeding on varied prey,” said the lead author of the study, Dr. Tom Stubbs, in a statement.

“Within a relatively short space of time, marine reptiles began feeding on hard-shelled invertebrates, fast-moving fish and other large marine reptiles. The range of feeding-related morphological adaptations seen in Triassic marine reptiles was never exceeded later in the Mesozoic.”

Studying the fossil record

The team came to these conclusions after carefully studying the fossil record of Mesozoic marine reptiles and using statistic to quantify the variation in the shape and function of jaws and teeth across these predators. Before now, studies had mostly been based on estimates of biodiversity across time. But this new study shook things up by tying the shape of jaws and teeth to their different modes of life (like their different modes of feeding).

“We always knew that the marine reptiles expanded relatively fast into a world in turmoil, after a devastating mass extinction event that killed as many as 95 per cent of species,” said co-author Professor Michael Benton.

“But what was unusual was that they were inventing entirely new modes of life that had not existed before the end-Permian mass extinction. Our work shows they expanded into nearly every mode of life, indicated by their feeding habits and range of body sizes, really much faster than might have been imagined.”

Interestingly, though, this sudden evolutionary burst took a sharp downturn within 30 million years. At this point—the Late Triassic—the marine reptiles started undergoing mass extinctions, wiping out most groups. The research from the University of Bristol shows that these extinctions eliminated many of the animals with specialized niches and morphological adaptations, and have had huge long-term effects on marine reptile evolution.

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Image credit: Listverse