The Loch Ness Monster

The most popular theory about the Loch Ness monster is that it's a please the a sore or something like that. How likely is it that a population of placeyosaurs could have survived the extinction of the dinosaurs? There have certainly been other ancient life forms that have survived hidden for millions of years like the coelacanth. So yes, creatures from dinosaur days can still exist and the Coelacanth is one of them. But there are differences between coelacants and placeyosaurs and these differences make it less likely that placeyosaurs would survive.