Monsters Part 3: Cretaceous Seas

Plesiosaurs were marine reptiles from which lived from around 220 million years ago, until about 65 million year ago. If you think of the normal depictions of the Loch Ness Monster, then you know what a classic plesiosaur looks like. They were large predators which live primarily on fish in the oceans whilst dinosaurs roamed the land and growing feathers. They ranged from having really long necks and small heads, to pretty much the opposite, small necks and big heads. They got about by having four rather large flippers, and essentially looked like a snake skeleton put inside a turtle shell, although they didn’t have a shell. They include things from the early 3m long beasties to possibly the largest predator to have existed, the aptly names “Predator X” (cue dramatic music).

This is Predator X, possibly 15m long, eating another plesiosaur

Plesiosaurs seem to have been coastal dwellers, as most fossils have been found in coastal and estuarine environments. They mainly fed on ammonites, hard-shelled molluscs similar in body-shape to the modern Nautilus, and Belemnites, creatures which were similar to squids. Larger varieties probably fed on smaller plesiosaurs, and some had teeth for crushing bony plates, like those on the armoured fish or turtles.

A classic image of a long-necked plesiosaur or elasmosaur

Possibly the most interesting thing about these creatures is not how they lived or anything about them at all. Some people want to think that plesiosaurs have lived on past their extinction in the K-T extinction, when the dinosaurs died. The strange thing is they have picked a hell of a spot to live. For some reason, these “modern plesiosaurs” have chosen a rather difficult environment to live in. You might think that living in salt water and fresh water are pretty much the same, but they aren’t. In salt water, you have the problem on keeping your water in and the salt out. This is basically because salt likes to disperse itself equally in a liquid. In Freshwater, you have the opposite problem, keeping your salt in and the water out. This might not be as much of a problem for large, skinned animals as it is for jellyfish (there aren’t many freshwater jellies), but it still does pose a big problem. Also, the majority of these lakes, like the quintessential Loch Ness, are in cold environments. Reptiles, especially marine reptiles, do not fare well in cold environments. Have a think of where the crocodiles live. They are pretty much an analogue of plesiosaurs, and they don’t live outside the tropics. This is basically because they don’t produce much heat in their bodies, and large bodies require lots of heat, so living in a lake that has an average temperature of 5.5°C! That and the fact that Loch Ness has only been there for about 12,000 years points to these cryptozoologists, as they are called, being wrong. These stories exist throughout the world, and they are all pretty much wrong. My favourite is the New Zealand lake monster in Lake Coleridge on the South Island. It’s called Lakey. Damn, New Zealand, that’s clever.

The most famous photo of the Loch Ness Monster, the Surgeon's Photo
 was probably an elephant.

Next is the terrifying Mosasaur.

Big, mean lizard-shark!

If you think back to Part 1 of this Monsters series, we met the Megalania. Well, good old mosasaur is pretty much a cross between that beast and a shark! They had mouths filled with long, pointy teeth, and had strong flippers and a powerful tail. They are relatives of snakes, which may surprise you, but they had very similar jaws, which allowed them to swallow their food whole. They hunted early birds, fish and sharks as well as eating smaller mosasaurs.

These things did get pretty big. Sure, the smallest were only about 3-3.5m long, but the biggest, one Tylosaurus, got to about 17.5m. They also seemed to have two sets of fangs, all the better to grab you with. These puppies lived pretty much worldwide, and seemed to prefer shallower waters. Generally, Mosasaurs were pretty successful as predators, as they seem to have had greater numbers than other predators in the sea. They outnumbered plesiosaurs and crocodiles, and seem to have filled the niche left over by the ichthyosaurs when they went extinct during the Cretaceous period. But, even being such great predators didn’t save these guys from the asteroid which did in the dinosaurs.

Mean, but at least they're all dead.

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