| There are also some studies that have shown many deep similarities between endothermy in birds and endothermy in mammals, which do not seem very likely to be the result of parallel evolution. So there are chances that actually endothermy was developed in the common ancestor of all amniotes. If that would be true, then various branches have reverted to poikilothermy, like modern crocodiles, turtles, lizards and snakes, in order to save energy and be able to live with less food, especially in water or at small sizes, when the energy consumption due to endothermy is great without a good thermal insulation. In this variant some dinosaur branches could have also reverted to poikilothermy. Regarding turbinates, even the crocodiles have a very simple form of them (and the lizards and snakes an even simpler form), so it is likely that most of the dinosaurs also had them, even if in a simpler form than in birds. The lack of turbinates in most dinosaur fossils might be a preservation artifact, because these are very thin and fragile bones. Googling shows that in cases of exceptionally good preservation of the skull, turbinates have been found in some dinosaurs, e.g. in Stegoceras. |
Dinosaurs span 165 million years there is enough room on an evolutionary time scale for them to take any shape and form.
That said the climate for much of their reign was very different, you probably didn’t had warm blooded aquatic life when the oceans were at 35c and finding dinosaurs in polar regions isn’t a proof for them being warm blooded as those region were tropical rain forests for about 90M years.