Third.

After trolling the web for more tasty climate related dinosaur fun, I came across this pearler:

Aha, I hear you say. What has that got to do with climate change and dinosaurs? Well, its pretty simple. And it makes a nice change to all that "massive asteroid explosion" theory we learnt when we were six. The late Cretaceous was a changing time, geological speaking, with several mountain building episodes, with many of the shallow seas drying up, as denoted by the red lines on with map, indicating the major subduction zones:

This lead to a massive drop in temperature, decreasing by around ten degrees. That kind of temperature drop is felt on a global scale. Dinosaurs are mainly found in warm and warm temperate zones (Figure 1.), and after studying their depositional environment, paleoecology and stomach contents of the herbivorous species, their preferred habitats are often associated with open grassland and marshland (Krassilov, 1981). As mountain building increased, and shallow seas disappeared, an increased seasonality occurred, favouring a particular group of plants: conifers.

Figure 1, Krassilov (1981). A= Northern temperate; B=Warm-temperate; C=Warm. Top Image: Jurassic. Lower Image: Cretaceous.

Van Valen and Sloan argued that dinosaurs were maladapted to these new forests, and migrated towards the tropics, supported by Krassilov's work mentioned above. However, the two papers differ in opinion on what exactly caused the extinction. Climate change is ubiquitous in both arguments, however Krassilov believes that the elimination of shrub land/marshland meant that the dinosaurs effectively died of starvation. Van Valen and Sloan argue however that the rise in in conifer forests lead to an unimpeded rise in mammal populations, as the dinosaurs did not venture into those areas, reducing competition.  These new mammal herbivores then descended from their conifer forest environment to plunder the dinosaur territories, leading to gradual extinction.

However, in my opinion, there are problems. In Van Valen's paper, he is effectively saying that herbivorous dinosaurs, multi tonne beasts, were out-competed in their territory, by newly radiated mammal species. It just doesn't seem plausible, as surely they were not big enough to oppose the late Cretaceous dinosaurs, and there carnivores roaming around who probably wouldn't have minded adding "mammals' to their diet. Also, it doesn't explain the extinction of the marine reptiles and pterosaurs, as well as several thousand marine invertebrate species either. What I think we should take from this paper is that dinosaur extinction was not as brutal as Alvarez and his team made it out to be with the impact crater theory.

And I leave you with this hilariously terrible image from Krassilovs paper. Is a Triceratops? Is it a turd? You decide.

http://www.scotese.com/images/Cretac94.jpg

http://www.paleobotany.ru/PDF/1980-1989/Krassilov_1981_changes.pdf

http://animals.howstuffworks.com/dinosaurs/dinosaur-extinction4.htm

Robert E. Sloan, J. Keith Rigby, Leigh M. Van Valen and Diane Gabriel. Gradual Dinosaur Extinction and Simultaneous Ungulate Radiation in the Hell Creek Formation Science, New Series, Vol. 232, No. 4750 (May 2, 1986), pp. 629-633