I was looking for my favorite book as a child when I stumbled across this website. It was a hardcover (thinner) book on Dinosaurs. The covers were gray, I believe it had a Tyrannosaurus Rex on the front cover, possibly in red writing.
Regretfully I don’t remember the exact title, just Dinosaurs, it was purchased around 1992.
Each page showed large depictions of each dinosaur in its natural habitat and some pictures were quite scary (or maybe that’s because I was a kid).
On the back cover or towards the back of the picture book it had a depiction of a Saber Tooth Tiger attacking or eating another dinosaur.
I have a book called The Great Dinosaur Atlas with a cover that doesn’t match what you describe, but there is another version called DK Great Dinosaur Atlas that sounds closer. You can google images to see them.
In the Time of the Dinosaurs 1963? Wrong back cover, though.
Search ETSY for “dinosaur book.” They have LOTS of books pictured.
Dinotopia?