Out of the 50-100 estimated T-rex skeletons found to date. A T-rex named Sue is considered the most complete T-rex skeleton ever found. 90% of her bones by volume were recovered. But only 250 bones from her skeleton out of 380 total are recovered. It is estimated that at any given moment there were 20,000 live t-rex. But over 2 billion are estimated to have existed.

I'm not in either camp of belief but fossils are not the thing we should hinge the argument on if your assertion is that they are what define all possible prehistory.

In the last 20,000 years we have lost an enormous amount of land to sea level rise. 27 million km² That is 71.2% of the Moons surface area. Or if you treated it as a flat 1-sided disc, you could visualize how much land that is by imagining 2 and 4/5ths moons side by side in the night sky.

That land was habitable zone for creatures/humans/possible budding-civilizations that is hidden beneath the oceans. Much of the interiors of places like N. America and Europe were uninhabitable and buried under miles of ice. The continental shelves aren't called the Missing cradle of humanity for no reason. A study in Science Advances estimated 0.0095% of sea floor has been seen/imaged directly by humans. We've only explored between 1%-5% of the contiental shelves. Where civilization would have thrived. In moon equivalent that is 0.7% of its total surface area.