Jurassic deep sea predators thrived as sea levels rose during the period while those that survived in the shallows became extinct, a new study found.
The change caused by climate hundreds of millions of years ago has implications for today’s species as the world’s oceans face the challenge of global warming.
A study of fossilised teeth showed just how reptiles adapted 150 million years ago.
And the study revealed for the first time that the broad structure of food chains beneath the sea has remained largely unchanged since the Jurassic era.
Various species fed off different food sources so they never had to compete and so could co-habitat – much like today’s sea life.
For more than 18 million years, diverse reptile species lived together in tropical waters that stretched from present-day northern France to Yorkshire
However, little was known about the structure of the food chain in this region called the Jurassic Sub-Boreal Seaway or how it changed as sea levels rose.
University of Edinburgh palaeontologists analysed the shape and size of teeth spanning this 18-million-year period when water levels fluctuated.
They found species belonged to one of five groups based on their teeth, diet and which part of the ocean they inhabited.
The pattern is very similar to the food chain structure of modern oceans, where many different species are able to co-exist in the same area because they do not compete for the same resources, the team says.
As sea levels rose, reptiles that lived in shallow waters and caught fish using thin, piercing teeth declined drastically.
But larger species which had broader teeth for crunching and cutting prey and inhabited deeper, open waters began to thrive.
The study suggested these deep-water species may have flourished as a result of major changes in ocean temperature and chemical make-up that also took place during the period
This could have increased levels of nutrients and prey in deep waters, benefitting species that lived there.
The study offers insights into how species at the top of marine food chains today might respond to rapid environmental changes – including climate change, pollution and rising temperatures.
Dr Davide Foffa, of the University of Edinburgh’s School of GeoSciences said: “Studying the evolution of these animals was a real – and rare – treat, and has offered a simple yet powerful explanation for why some species declined as others prospered.
“This work reminds us of the relevance of palaeontology by revealing the parallels between past and present-day ocean ecosystems.”
Dr Steve Brusatte, Reader in Vertebrate Palaentology also in the School of GeoSciences, added: “Teeth are humble fossils, but they reveal a grand story of how sea reptiles evolved over millions of years as their environments changed.
“Changes in these Jurassic reptiles parallel changes in dolphins and other marine species that are occurring today as sea-levels rise, which speaks to how important fossils are for understanding our modern world.”
The study which also involved the University of Bristol, was published in the journal Nature Ecology & Evolution.
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