Forty million years before T-rex. Imagine all of the species which appeared and became extinct during that time period. Some of them were never recorded in the annals of sedimentary history.
Tyrannosaurs show their sensitive side
A team of researchers has found a new species of tyrannosaur dinosaur -- the most popular of the prehistoric creatures. After the fossils were pulled out of the muddy banks of a Montana river, the team was able to analyze the texture of the facial bones of the new species. The findings suggest that the face of tyrannosaurs was covered in a scaly protective layer with a high degree of tactile sensitivity, similar to crocodiles. Ref. Source 9z.
So, they probably tended to their young by using their snouts. Interesting tidbit of information. I wonder why they developed with their arms as small as they are. Had they been a bit longer they'd have been even more fearsome and possibly a bit more intelligent too as they evolved to use their arms for other things. Instead, they evolved to have virtually useless arms. This is a strange evolution to me.
How many T. Rexes were there? Billions. With fossils few and far between, paleontologists have shied away from estimating the size of extinct populations. But UC Berkeley scientists decided to try, focusing on the North American predator T. Rex. Using data from the latest fossil analyses, they concluded that some 20,000 adults likely roamed the continent at any one time, from Mexico to Canada. The species survived for perhaps 2.5 million years, which means that about 2.5 billion lived and died overall. Ref. USAToday.