Dinosaurs Sequence 42

We are in the early Maastrichtian in an area that will one day come to be known as Russia. A huge lake stretches out to the horizon. This is Poteryali Lake, a remnant of a receding sea. A herd of Kundurosaurus walk towards the lake shore. These hadrosaurs are common here, unlike many other animals in the region, the Kundurosaurus stay here all year. They walk up to the lake shore and drink. Some of them begin to feed on the plants surround Poteryali Lake. The hadrosaurs padded feet crunch on the black sand of the lake’s beaches. However, there are much more unusual creatures in the lake than outside of it.
The tip of a snout peeks out of the dark water to take a breath. This is a Mosasaurus beaugei poteryalii, and it is one of the most unique marine reptiles in the world. When the sea retreated and Poteryali Lake was left behind, the lake itself wasn’t the only thing that was. A small population of saltwater Mosasaurus were trapped in this lake. Over time, they have adapted to survive in this, one of the most extreme environments in the world.
The Mosasaurus dives back down under the surface and into the dark world below. The surface of the lake is covered with pack ice and the water is freezing, but the Mosasaurus have a thick layer of blubber, thicker even than that of the arctic mosasaur Prognathodon, to keep them warm. He swims deeper and deeper still until it is almost pitch black. He cannot see clearly, but he can tell if prey comes near enough. He sends out high-pitched clicks, a primitive form of echolocation, in order to detect his prey.
Above a shoal of salmon-like fish, known as Salmonodon poteryaliensis, swim, completely unaware of the predator lurking below. The Mosasaurus stalks the shoal, and, when he gets close enough, shoots upward and attacks. Many of the fish get away but the Mosasaurus catches and eats plenty of them. He them swims back up to the surface and rests in the shallows. When he wakes up, a Kundurosaurus is looking at him curiously. The Mosasaurus squeaks in alarm and leaps back into deeper water.
No longer hungry, our Mosasaurus swims around on the surface between the ice floes. Another animal is swimming among the waves. It is a stagodont similar to Didelphodon. Much like sea otters, these stagodonts often float on their backs and rest. He knows he has nothing to fear from the Mosasaurus and continues floating around. Another swims past and dives under the water. He grabs a stone from the bottom and places it on an ice floe, then dives back down. He searches around on the bottom for a minute before he spots part of a shell. He pulls out the mussel and swims back up to the surface. He grabs the stone and beats the mussel until the shell cracks. Then he starts eating it.
Life will go on the same way here for the next few millions of years. Here in one of the strangest marine reptiles of all lives and hunts, and eventually they will be forgotten. This unique habitat will disappear, not to be seen again for nearly 70 million years.