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According to a new study from the University of Edinburgh, the deep-water Jurassic reptiles thrived as sea level rose, while species in shallow waters disappeared.
An artistic impression of Jurassic marine reptiles. Image credit: Nikolay Zverkov.
For more than 18 million years, various species of reptiles cohabited in a single seaway called the Subboreal Jurassic Way of the United Kingdom.
Until now, however, little was known about the structure of the food chain in this region or its evolution as sea level increased.
By analyzing the shape and size of the teeth during this period of fluctuating water levels, University of Edinburgh palaeontologist Davide Foffa and his colleagues found that the species belonged to one of five groups.
The scheme is very similar to the structure of the modern ocean food chain, where many different species can coexist in the same area because they are not competing for the same resources.
"Studying the evolution of these animals was a rare treat and provided a simple but powerful explanation of why some species declined as others thrived," said Foffa.
"Teeth are humble fossils, but they tell a great story of how marine reptiles have evolved over millions of years as their environment has changed," said Dr. Steve Brusatte, also an author.
"The changes in these Jurassic reptiles are parallel changes in the dolphins and other marine species that occur today, as sea levels rise, which shows how important fossils are." to understand our modern world.
Partial disparity of marine reptiles of the Jurassic sub-boreal seaway, as a function of global sea level: (a) partial disparity of taxonomic groups; (b) partial disparity of food guilds; c) sea-level curve, with the fossil-rich intervals of the sub-boreal seaway noted. Fm – Training. Image credit: Foffa et al, doi: 10.1038 / s41559-018-0656-6.
The team found that the sea level in the world was increasing, Jurassic reptiles that lived in shallow waters and captured fish with fine, piercing teeth.
At the same time, larger species that lived deeper, open waters began to thrive. These reptiles had larger teeth to chew and cut prey.
"The deepwater species may have thrived as a result of major changes in ocean temperature and chemical composition that also occurred during the period," the researchers said.
"It could have increased levels of nutrients and prey in deep waters, benefiting the species that lived there."
The results were published online this week in the journal Ecology of nature and evolution.
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Davide Foffa et al. The ecology and long-term evolution of marine reptiles in a Jurassic seaway. Ecology of nature and evolution, published online September 3, 2018; doi: 10.1038 / s41559-018-0656-6
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