Phys.org has a story about the state of the non-avian dinosaurs just before the K-Pg mass extinction about 66 million years ago.  For a while, it was thought they were in decline before the asteroid strike.  A new study published in the journal Science Advances found that the non-avian dinosaurs were actually thriving, entrenched in stable niches.  They weren’t slipping toward inevitable extinction.

Scientists have long debated why non-bird dinosaurs, including Tyrannosaurus rex and Triceratops, became extinct—whereas mammals and other species such as turtles and crocodiles survived.

The new study, led by an international team of paleontologists and ecologists, analyzed 1,600 fossil records from North America. Researchers modeled the food chains and ecological habitats of land-living and freshwater animals during the last several million years of the Cretaceous, and the first few million years of the Paleogene period, after the asteroid hit.

Paleontologists have known for some time that many small mammals lived alongside the dinosaurs. But this research reveals that these mammals were adapting to their environments and becoming more important components of ecosystems as the Cretaceous unfolded. Meanwhile, the dinosaurs were entrenched in stable niches to which they were supremely well adapted.