Ninth

Here's a good article regarding the Cretaceous/Tertiary mass extinction event:

The K/T (or K/Pg, as it is now known) is most famous for killing the dinosaurs, however it must be noted that many species suffered catastrophic losses, including the ancestors of the present day birds and mammals, who are often seen as those who "survived" the event.

What is interesting in this paper is the fact that the asteroid impact in the gulf of Mexico is to blame for the extinction, and does not seem to reference climate change as a major factor, however the authors may be inferring a climate-driven change as a result of a bollide impact. Secondly, it is also interesting to note that snakes and lizards were as diverse as the dinosaurs during the late Cretaceous, but the research done by Longrich and his team suggests almost 83% of lepidosaurs (snakes and lizards) went extinct along with the dinosaurs, making the modern representatives, as Longrich says, successful by "default". They were not better adapted than their lepidosaur cousins, they just radiated after the extinction event because they were not competing with them.

Its an interesting read, if a little off topic, but puts in perspective the end Cretaceous extinction, revealing Dinosaurs weren't the only ones to suffer 65 million years ago.