Plesiosaur fossils found in the desert indicate that they were not just marine animals

Plesiosaur fossils found in the desert indicate that they were not just marine animals

Credit: University of Bath

Fossils of small plesiosaurs, long-necked marine reptiles from the age of dinosaurs, have been found in a 100-million-year-old river system that is now the desert of Morocco. This discovery suggests that some species of plesiosaur, traditionally thought to be marine creatures, may have lived in freshwater.

First found in 1823 by fossil hunter Mary Anning, Plesiosaurs were prehistoric reptiles with small heads, long necks, and four long flippers. They inspired the reconstruction of the Loch Ness monster, but unlike the Loch Ness monster, plesiosaurs were marine animals — or were widely believed to be.

Now, scientists from the University of Bath and University of Portsmouth in the UK, and Hassan II University in Morocco, have reported tiny plesiosaur rocks from the Cretaceous river in Africa.

The fossils include the bones and teeth of a three-meter-long adult and an arm bone of a 1.5-meter-long child. They noted that these creatures routinely lived and fed in freshwater, along with frogs, crocodiles, turtles, fish and the huge aquatic dinosaur Spinosaurus.

These fossils indicate that plesiosaurs were adapted to withstand fresh water, and may have spent their lives there, like river dolphins today.

The new paper was led by University of Bath student Georgina Bunker, along with Nick Longrich from the University of Bath’s Milner Center for Evolution, David Martell and Roy Smith from the University of Portsmouth, and Samir Zuhri from Hassan II University.

Plesiosaur fossils found in the desert indicate that they were not just marine animals

Kem Kem plesiosaur silhouettes. Credit: University of Bath

The fossils include vertebrae from the neck, back, and tail, deciduous teeth, and an arm bone from a small juvenile.

said Dr. Nick Longrich, corresponding author on the paper.

“Bone and teeth were found scattered and in different places, not as a skeleton. So every bone and every tooth is a different animal. We have more than a dozen animals in this group.”

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

Plesiosaur fossils found in the desert indicate that they were not just marine animals

Humerus plesiosaur. Credit: University of Bath

Moreover, the teeth show heavy wear, like the fish-eating dinosaurs Spinosaurus in the same family.

Scientists say this indicates that the plesiosaurs were eating the same food – cutting their teeth on 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 such as whales and dolphins roam the rivers, either to feed or because they are missing, the number of plesiosaur fossils in the river suggests that it is unlikely.

The most likely possibility is that plesiosaurs were able to tolerate both fresh and salt water, as did some whales, such as the beluga whale.

Plesiosaur fossils found in the desert indicate that they were not just marine 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 the plesiosaurs allowed them to fish in shallow rivers, and the fossils show an incredibly rich fish fauna.

Dr Longrich said: “We don’t really know why plesiosaurs were in freshwater.

“It’s a bit controversial, but who would say that because we paleontologists have always called them ‘marine reptiles,’ they had to live in the sea? A lot of marine lineages have invaded the freshwater.”

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

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

Plesiosaurs were a diverse and adaptable group, and have been around for more than 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 frequently, to varying degrees.

“We don’t really know, frankly. This is how paleontology works. People wonder, how can paleontologists know anything for sure about the lives of animals that went extinct millions of years ago? The truth is we can’t always. It’s about making informed guesses based on the information we have. We’ll find more fossils. Maybe they’ll confirm those guesses. Maybe not.”

“It was really exciting to see the direction this project is going,” said lead author Georgina Bunker. The study initially began as a university project involving a single bone, but over time, more plesiosaur fossils began to emerge, providing a clearer picture of the animal.

The new discovery also expands the diversity of Cretaceous Morocco. Dr. Samir Zuhri said, “This is another exciting discovery that adds to the many discoveries we have made in the Kim Kim over the past 15 years of working in this region of Morocco. The Kim Kim was truly a biodiversity hotspot in the Cretaceous period.”

Co-author Dave Martell said, “What amazes me is that the ancient Moroccan river had so many carnivores all living side by side. This was not a place to swim.”

But what does all this mean for the Loch Ness monster? On one level, this is reasonable. Plesiosaurs were not confined to the seas, they inhabited fresh waters. But the fossil record also indicates that after approximately one hundred and fifty million years, the last plesiosaurs became extinct at the same time as the dinosaurs, 66 million years ago.

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more information:
Georgina Bunker et al, Plesiosaurs of the riverine Kem Kem group (mid-Cretaceous) from eastern Morocco and a review of non-marine plesiosaurs, chalk search (2022). DOI: 10.1016 / j.cretres.2022.105310

Presented by the University of Bath

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