I tried my best coming up with a speculative creature for the tournament that I had to use my book. And by the way, meet Oploconasaurus. (Armored cone lizard) And no it's not an Ankylosaur and Plesiosaur hybrid.
This is an armored plesiosaur-like herbivore. It's not very fast at swimming but it has cone like armor that makes up its neck and tail, and a tail club with two spikes. It is about 9 m long and lived in cooler climates in the Cretaceous and Paleocene.
As for its behavior it eats aquatic vegetation and it can bury half of its body in the ground. It can also break rocks into pieces and swallow it for digestion.
Here it goes in the tournament and I can't wait to see the others!