Fossils of small plesiosaurs, long-necked marine reptiles from the dinosaur age, have been found in a 100-million-year-old river system that is now Morocco’s Sahara Desert. This discovery suggests that some species of Plesiosaurus, traditionally thought of as marine animals, may have lived in freshwater.
Plesiosaurs, first found in 1823 by fossil hunter Mary Anning, were prehistoric reptiles with small heads, long necks and four long fins. They inspired reconstructions of the Loch Ness monster, but unlike the Loch Ness monster, plesiosaurs were sea creatures — or so it was commonly believed.
Now scientists from the University of Bath and the University of Portsmouth in the United Kingdom, and the Université Hassan II in Morocco, have reported small plesiosaurs from a Cretaceous river in Africa.
The fossils include bones and teeth of three-meter-long adults and an arm bone of a 1.5-meter-long baby. They suggest these creatures routinely lived and fed in freshwater, alongside frogs, crocodiles, turtles, fish and the huge aquatic dinosaur Spinosaurus.
These fossils suggest that the plesiosaurs were adapted to tolerate fresh water, possibly even spending their lives there, like today’s river dolphins.
The new paper was led by student Georgina Bunker from the University of Bath, along with Nick Longrich from the University of Bath’s Milner Center for Evolution, David Martill and Roy Smith from the University of Portsmouth and Samir Zouhri from Hassan II University. .
The fossils include vertebrae from the neck, back and tail, shed teeth and an arm bone from a young juvenile.
“It’s a mess, but isolated bones tell us a lot about ancient ecosystems and animals in them. They’re so much more common than skeletons, they give you more information to work with,” says Dr. Nick Longrich, corresponding author of the paper.
“The bones and teeth were scattered and found in different places, not as a skeleton. So every bone and every tooth is a different animal. We have over a dozen animals in this collection.”
While bones provide information about where animals died, the teeth are interesting because they were lost while the animal was alive, so they show where the animals lived.
In addition, the teeth show heavy wear, like that fish-eating dinosaur Spinosaurus found in the same beds.
The scientists say this implies that the plesiosaurs ate the same food: their teeth crumbling on the armored fish that lived in the river. This indicates that they spent a lot of time in the river, rather than being occasional visitors.
While marine animals such as whales and dolphins roam rivers, either for food or because they are lost, the number of plesiosaur fossils in the river suggests this is unlikely.
A more likely possibility is that the plesiosaurs could tolerate fresh and salt water like some whales, such as the beluga whale.
It is even possible that the plesiosaurs were permanent inhabitants of the river, like modern river dolphins. Their small size would allow the plesiosaurs to hunt in shallow rivers, and the fossils show an incredibly rich fish fauna.
dr. Longrich said, “We don’t really know why the plesiosaurs are in freshwater.
“It’s a bit controversial, but who’s to say that because we paleontologists have always called them ‘marine reptiles,’ they had to live in the sea? Many marine genera have invaded freshwater.”
Freshwater dolphins have evolved at least four times – in the Ganges River, the Yangtze River and twice in the Amazon. A species of freshwater seal lives in Lake Baikal, in Siberia, so plesiosaurs may have adapted to freshwater as well.
The plesiosaurs belong to the family Leptocleididae – a family of small plesiosaurs commonly found in brackish or fresh water elsewhere in England, Africa and Australia. And other plesiosaurs, including the long-necked elasmosaurs, are popping up in brackish or fresh water in North America and China.
Plesiosaurs were a diverse and adaptable group, having been around for over 100 million years. Based on what they found in Africa — and what other scientists have found elsewhere — the authors suggest they may have repeatedly invaded freshwater to varying degrees.
“We honestly don’t really know. That’s how paleontology works. People wonder, how can paleontologists know anything for sure about the life of animals that went extinct millions of years ago? The reality is we can’t always do that. What can we do? is making educated guesses based on the information we have. We’ll find more fossils. Maybe they’ll confirm those guesses. Maybe not.”
“It has been very interesting to see where this project has gone,” said lead author Georgina Bunker. The study initially started out as an undergraduate project involving a single bone, but over time, more plesiosaur fossils began to surface, slowly providing a clearer picture of the animal.
The new discovery also increases the diversity of the Cretaceous of Morocco. dr. Samir Zouhri said: “This is another sensational discovery that adds to the many discoveries we have made over the past fifteen years in this region of Morocco in the Kem Kem. Kem Kem was a truly incredible biodiversity hotspot in the Cretaceous. “
“What amazes me,” said co-author Dave Martill, “is that the ancient Moroccan river had so many carnivores all living side by side. This was no place to swim.”
But what does all this mean for the Loch Ness Monster? On one level it is plausible. Plesiosaurs were not limited to the seas, they lived in fresh water. But the fossil record also suggests that after nearly 150 million years, the last plesiosaurs finally died at the same time as the dinosaurs, 66 million years ago.
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Georgina Bunker et al., Plesiosaurs from the fluvial Kem Kem group (Mid Cretaceous) of eastern Morocco and a survey of non-marine plesiosaurs, Chalk research (2022). DOI: 10.116/j.cretres.2022.105310
Provided by the University of Bath
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