> the researchers were able to approximate that about 20,000 T. rex were alive at any given time
low
low
1. Water covers ~70% of the Earth's surface. Whales migrate of course but can exist from the poles to the equator;
2. Of the 30% land, for pretty much any species, some portion of that is uninhabitable. Dinosaurs being reptiles likely require hot and wet environments. As predators, T. Rex would be limited by where their food could live too.
The dinosaur era was largely one of a super-continent (Pangaea). A good portion of that was likely too cold or too dry to support such a large predator.
They lived in what is now Western North America, but was then an island continent called Laramidia [1] so yes, they were geographically quite limited.
The spatial distribution and population density of tigers in mountainous terrain of Bhutan "Based on our top model, the estimated tiger population size (N) was 91 individual tigers with 60 adult females and a density of 0.24 tigers/100 km2 "