Short answer. "no" species evolve and change. Without necessarily dying out. The Dinos were spectacularly successful and this theory is just ignorant and smacks of old school thinking. The Dinos of today would be likely different but still Dinos. You need to see them as a genera over millions of years. Not a few species.
Dinosaurs were the dominant organism on this planet from the late Triassic period all the way to the Cretaceous, they didnt stay that way by being the same. They adapted and branched off into countless variants over what what seem like eons to us.
The problem with this theory is that there already WAS an abundance of diversity during the time of the dinosaurs. Fish, insects, lesser mammals, smaller reptiles, amphibians, all of these were around and thriving during the saurian era.
Heck, there were dinosaurs that were already making the change into birds as early as the late Jurassic period, Acheopteryx was one of these.
All this paper is saying is that the ecosystem--not the dinosaurs themselves--was less diverse than it was thirteen million years before. This is true, because the Niobrara Sea actually dried up about 80 million years ago.