Spinosaurus

Ngume-monenes are one of the largest predators in the swamp basins they reside within. Measuring fifty feet long and weighing around nine tons, these behomoths are recognized by their large sails running down their backs as tall as a man, their crocodilian maws are just as long with piercing teeth that can easily pierce through the hides of fish. These colossal predators can easily swim through the water with their paddle tails and webbed feet. 

These large crocodilian dinosaurs lay easily spend their time either swimming through the water and snagging passing fish to standing on the surface and feeding like a heron. Thankfully they are very patient with humanoids allowing them to walk up to around twenty feet near them before reacting and most of these are warnings of rearing up and hissing with their arms outstretched.

It is unknown what causes it, some believe it is through a deep connection of the Ngume-monene's amphibious lifestyle linking it towards the ancient race known as the Batrachi, an ancient race connected to amphibian races and doppelgangers, and others believe it was purely from simply the result of arcane mutation gone awry. 

For whatever the case, some of these beasts have the ability to alter their body plans to drastically different forms allowing for adopting more terrestrial to more aquatic plans with as little as six hours of their body transmutating, one anecdote tells of one that had achieved flight by these magical means.