Plesiosaur fossils found in the Sahara suggest they weren’t just sea animals

Credit: University of Bath

Fossils of small plesiosaurs, long-necked marine reptiles from the age of dinosaurs, have been discovered in a 100 million-year-old river system that is now Morocco’s Sahara Desert. This discovery suggests that some species of plesiosaurs, traditionally considered sea creatures, may have lived in fresh water.

Plesiosaurs, first discovered 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 marine animals – or were widely believed to be such.

Now scientists from the University of Bath and the University of Portsmouth in the UK, and Hassan II University in Morocco, have reported small plesiosaurs from a Cretaceous river in Africa.

The fossils include adult bones and teeth three meters long and a baby’s arm bone 1.5 meters long. They hint that these creatures regularly lived and fed in fresh water, alongside frogs, crocodiles, turtles, fish, and the massive aquatic dinosaur Spinosaurus.

These fossils suggest that plesiosaurs were adapted to tolerate fresh water, possibly even spending their lives there, like today’s river dolphins.

The new journal was edited by Georgina Bunker, a student at the University of Bath, with Nick Longrich from the Milner Center for Evolution at the University of Bath, David Martill and Roy Smith from the University of Portsmouth and Samir Zouhri from the University Hassan II.

Plesiosaur fossils found in the Sahara suggest they weren't just sea animals

Kem Kem plesiosaur silhouettes. Credit: University of Bath

Fossils include neck, back and tail vertebrae, lost teeth and an arm bone from a young juvenile.

“It’s scrappy stuff, but isolated bones tell us a lot about ancient ecosystems and the animals that are there. They’re so much more common than skeletons, they give you more information to work with,” said said Dr. Nick Longrich, corresponding author on the paper.

“The bones and teeth were found scattered and in different localities, not in skeletal form. So each bone and each tooth is a different animal. We have over a dozen animals in this collection.”

While the bones provide information about where the animals died, the teeth are interesting because they were lost while the animal was alive, so they show where the animals lived.

Plesiosaur fossils found in the Sahara suggest they weren't just sea animals

Plesiosaur humerus. Credit: University of Bath

Also, the teeth show heavy wear, like those fish-eating Spinosaurus dinosaurs found in the same beds.

Scientists say this implies the plesiosaurs ate the same food – chipping their teeth off the armored fish that lived in the river. This suggests that they spent a lot of time in the river, rather than being occasional visitors.

While marine animals like whales and dolphins travel up rivers, either to feed or because they are lost, the number of plesiosaur fossils in the river suggests this is unlikely.

A more likely possibility is that plesiosaurs were able to tolerate both fresh and salt water, like some whales, such as the beluga.

Plesiosaur fossils found in the Sahara suggest they weren't just sea animals

Credit: University of Bath

It is even possible that plesiosaurs were permanent residents of the river, like modern river dolphins. The small size of plesiosaurs would have allowed them to hunt in shallow rivers, and fossils show an incredibly rich fish fauna.

Dr Longrich said: “We don’t really know why plesiosaurs are in fresh water.

“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 lineages invaded fresh water.”

Freshwater dolphins have evolved at least four times – in the Ganges, the Yangtze River and twice in the Amazon. A species of freshwater seal inhabits Lake Baikal, Siberia, so it is possible that plesiosaurs also adapted to freshwater.

Plesiosaurs belong to the family Leptocleididae, a family of small plesiosaurs often found in brackish or fresh water elsewhere in England, Africa and Australia. And other plesiosaurs, including the long-necked elasmosaurs, are found in brackish or freshwater in North America and China.

Plesiosaurs were a diverse and adaptable group, and had been around for over 100 million years. Based on what they found in Africa – and what other scientists have found elsewhere – the authors suggest that they may have invaded freshwater multiple times to varying degrees.

“Honestly, we don’t really know. This is how paleontology works. People ask, how can paleontologists know for sure the lives of animals that died out millions of years ago? The reality is that we can’t always. can do is make educated guesses based on the information we have. We will find more fossils. Perhaps they will confirm these assumptions. Maybe not.

“It’s been really interesting to see the direction this project has gone in,” said lead writer Georgina Bunker. The study first began as an undergraduate project involving a single bone, but over time more plesiosaur fossils began to appear, slowly providing a clearer picture of the animal.

The new discovery also expands the diversity of Morocco’s Cretaceous. Said Dr. Samir Zouhri, “This is another sensational discovery that adds to the many discoveries we have made in Kem Kem over the past fifteen years of work in this region of Morocco. Kem Kem was truly a hotspot of incredible biodiversity in the Cretaceous.”

“What amazes me,” said co-author Dave Martill, “is that the ancient Moroccan river contained so many carnivores all living side by side. It was no place to go for a swim.”

But what does all this mean for the Loch Ness Monster? On some level, it’s plausible. Plesiosaurs were not confined to the seas, they inhabited fresh water. But the fossil record also suggests that after nearly one hundred and fifty million years, the last plesiosaurs finally died out along with the dinosaurs, 66 million years ago.

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More information:
Georgina Bunker et al, Plesiosaurs from the Kem Kem (Middle Cretaceous) fluvial group of eastern Morocco and review of non-marine plesiosaurs, Cretaceous research (2022). DOI: 10.1016/j.cretres.2022.105310

Provided by the University of Bath

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