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

Now, scientists from the University of Bath and University of Portsmouth in the U.K., and Université Hassan II in Morocco, have reported small plesiosaurs from a Cretaceous-aged river in Africa.

The fossils include bones and teeth from three-meter long adults and an arm bone from a 1.5 meter long baby. They hint that these creatures routinely lived and fed in freshwater, alongside frogs, crocodiles, turtles, fish, and the huge aquatic dinosaur Spinosaurus.

These fossils suggest the plesiosaurs were adapted to tolerate freshwater, possibly even spending their lives there, like today's river dolphins.

The new paper was headed by University of Bath Student Georgina Bunker, 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 the Universite Hassan II.

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

"It's scrappy stuff, but isolated bones actually 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" said Dr. Nick Longrich, corresponding author on the paper.