Up until this time people had not realised that there were many extinct animals that were very different to the animals alive now.
The one Georges Cuvier studied we now call a Mosasaur. It was a huge carnivorous sea reptile. It's the "Sea rex" we mentioned earlier.
This is the play again, this time as a slide-and-sound show:
Here, again, is the documentary film about the Mosasaur that we watched some of: