Sixth.

GSD vs TSD. Probably not something you come across everyday. In a (relatively) recent article Miller and his team (2004), the sex determination of organisms, including dinosaurians, was analysed:

 Sex determination is essentially how a male or a female is allocated its sex during its embryo stage of development. GSD, or genetic sex determination, uses sex chromosomes (X and Y) or genes (such as SRY gene in mammals) to produce a male or female foetus. In TSD organisms, temperature plays a key role, above or bellow a certain temperature produces one of the two sexes, a trait seen in alligators and turtles, for example. The sex determination methods in dinosaurs cannot be known due to the nature of the fossil record, however it can be inferred via their phylogenetic relationship to other animals. 

The above graph shows the sex determination method in animals and their phylogenetic relationship. Dinosaurs, being archosaurs, are close relatives of crocodiles, which use TSD to determine offspring sex. Further evidence is found in the offspring, as dinosaur and alligator infants share well developed prenatal pelvic girdles, inferring a similar nesting style in both groups.  

At the K/T boundary, famed for the extinction of the dinosaurs and 65% of life on earth, undoubted climatic change occurred, after millions of years of favourable climates that meant dinosaurs had no need to switch to GSD. A change in temperature skewed the sex ratio of the dinosaurs towards a male-based environment, thus causing an impossible recovery from the events at the K/T boundary

However, this article is filled with inaccuracies. Firstly, there is no concrete proof for TSD in dinosaurs, and the evidence Miller (2004) has suggested is wrong: he writes that dinosaurs had a reptilian breathing mechanism rather than an avian one, thus circulation was more likely to resemble ectothermic crocodilians. However, as in my last post, dinosaurs are seen to have avian style breathing, and were in fact probably exothermic creatures. Thus, GSD could have arisen in dinosaurs in the same way as it arose in birds, rendering the argument obsolete.

http://www.infertile.com/pdf_files/archive/2004_FertStert_EnvironmentalSex.pdf