All the evidence shows us the pterosaurs are cousins of dinosaurs and that both share a common ancestor.

Mike Benton

It became clear that there were two main factors, first that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures, then, the loss of herbivores made the ecosystems unstable and prone to [an] extinction cascade. We also found that the longer-lived dinosaur species were more liable to extinction, perhaps reflecting that they could not adapt to the new conditions on Earth.