66 million years ago, the dinosaur empire was in its death throes when its final nail in the coffin came hurtling down from the sky. A clump of rock the size of Mount Everest smashed into the Gulf of Mexico, bringing about the end of 70-75% of all species. Oh, the dinosaurs are still alive, don't get me wrong, but the glory days of their empire died when that bolide hit the Earth.
Now, it is a popular trope among the speculative evolution subgenre to imagine what life was like if Chicxulub never struck the planet and the dinosaur empire was left to continue. Results vary from the sub-par Dougal Dixon book The New Dinosaurs to the more elaborate, more detailed and more enjoyable Speculative Dinosaur Project.
But I would like to take this a little differently. In this alternate Earth, Chicxulub hit the Gulf of Mexico not at the end of the Cretaceous period 66 million years ago, but the end of the Jurassic period, 145 million years ago. Back then, the dinosaur empire was at its prime, with dinosaurs conquering every corner of the globe, occupying virtually every niche imaginable, from sparrow-sized Epidexipteryx to the extra-long sauropod Diplodocus.
The key element that the survivors of the fall of the dinosaur empire in our timeline had was their size. No one larger than 25 kilograms (or 55 pounds) stood a chance. As far as I know, any of the nonavian dinosaurs at the end of the Cretaceous exceeded that maximum limit, and that was the cause of their downfall. The dinosaurs at the end of the Jurassic, on the other hand, were noticeably different, with different lineages, different environmental preferences, different diets, different size ranges (some species at the time could certainly top the intended maximum survival limit of 25 kilograms) and different methods of adaptation.
Based on our knowledge of the fauna of the late Jurassic period (163.5 million years ago to 145 million years ago), would any of the dinosaurs within that timeframe survive a Chicxulub-sized impact, thus ensuring the continued survival of the dinosaur empire?