Fourth.

Evening ladies and gents. Today's blog will look at how a species evolved in changing climatic conditions to become one of the top predators in its habitat, and it is not a mighty tyrannosaur that takes centre stage. Its a smaller theropod who goes by the name Troodon. Lets start off with the basics. By definition, members of the Troodon are small, bipedal carnivores, best known for their large brains and inferred cerebral capabilities. Found during the late Cretaceous, they weighed in at no more than 50kg. That's about twenty times smaller than the Gorgosaurus  (centre right) in the picture above. It was their brain power that gave them a vast predatory arsenal, using speed and communication to hunt.

However, during the Maastrichian, climate fluctuations meant that the polar regions got colder and saw less daylight (Wolfe and Upchurch, 1987). And as a general rule, the colder it gets, the fewer predators you come across. This can be seen in Alaska's fossil record: fewer than one percent of the 3000 bones collected there show predator tooth marks (Gangloff, 2012). However, of the predators found in the arctic circle, Troodon is very well represented. This is where it gets interesting. The teeth this far north are twice as big as those found south. That means where looking at predators twice as big as they should be: nearing the 100kg mark. 

Now, I'm not saying that these larger Troodon are the same species as their southern representatives, but they are of the same tribe, and thus extremely similar. This shows how climate has affected the small theropod, and it has responded accordingly. It's already large eyes meant it had no problem hunting in the perpetual night that surrounds the area for most of the year. And the probable feathered covered skin helped with heat retention. The interesting morphological change is the doubling of its mass. Surely having more mass means larger energy expenditure? It probably is the case.  But being larger helps with heat rentention, as they now possess a smaller surface area to volume ratio compared to their smaller cousins. Put a feather coat on top of that and they were pretty toasty.

This doubling in size also means that it can tackle larger prey, which was abundant for the same body heat retention (check out the gigantothermy model for more info). Working together to haul down large Edmontosaurus for example, meant that Troodon was king of the Acrtic.

-http://blogs.smithsonianmag.com/dinosaur/files/2011/05/March-of-the-dinosaurs-promo.jpg
-http://www.clim-past-discuss.net/4/981/2008/cpd-4-981-2008.pdf
-Fiorillo, Anthony R.; Gangloff, Roland A. (2000). "Theropod teeth from the Prince Creek Formation (Cretaceous) of Northern Alaska, with speculations on Arctic dinosaur paleoecology". Journal of Vertebrate Paleontology 20(4): 675–682.
-http://books.google.co.uk/books?id=iriTYIpQV4IC&pg=PA100&lpg=PA100&dq=arctic+troodon+teeth&source=bl&ots=Q-pNtJu30w&sig=0DZe0Hcu99BPegpe_tChXLdhUEU&hl=en&sa=X&ei=bRuMUNitBebO0QXE1YDgDQ&ved=0CEIQ6AEwBQ#v=onepage&q=arctic%20troodon%20teeth&f=false
-http://3.bp.blogspot.com/-WbOR1Wk4x7E/UBspJOtFc-I/AAAAAAAABGE/zFaPmA2U0yk/s640/alaska2.png

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 

Second.

What better place to start my first "proper" blog post about dinosaurs and climate change than the following newspaper article:

Telegraph, 2012

At first I was sceptical about it, I labelled study leader Dr. Wilkinson as a embarrassment to palaeontology. The notion is just ridiculous: dinosaurs farted so much they caused global warming. But as I began to read it, I realised the bloke had a point. Lets start at the basics. Cows are herbivores. They eat grass. Grass contains cellulose an indigestible compound that can only be broken down by the enzyme cellulase, found in bacteria. So it's pretty handy that cows, along with other ruminants, have a gut full of the microbes. As the cows eat the grass, the plant matter ferments in the anaerobic conditions of the gut, producing methane. Simple. It is estimated that modern day herbivores account for 45 to 90 million tonnes of methane per year. 

Wilkinson, 2012

Cows, compared to the majority of dinosaurs, are insignificantly small. Sauropods, measuring up to 40m in length and a anything above 40 tonnes in weight, would have had gut flora unlike anything seen in modern day ecosystems. And their cellulose digesting bacteria had a huge daily income of plant matter entering the enormous digestive cavity. After doing a clever bit of maths, Dr. Wilkinson estimated that the animals produced around 472 million tonnes of methane per year. Today's total of natural and man made emissions: around 181 million tonnes per year. 

According to the study, Sauropods alone would have been responsible for adding an atmospheric concentration of 1-2 parts per million. And this is without adding the ceratopsians, hadrosaurs, ankylosaurs, nodosaurs,stegosaurs, heterodontosaurs, just to name a few, to the mix.

The moral of this story is: to prevent global warming, kill all large herbivores. Sucks for you, Mr. Elephant...

http://www.telegraph.co.uk/science/dinosaurs/9250032/Dinosaurs-passing-wind-may-have-caused-climate-change.html

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhyO1rqqFX6qTC9vtOqY04DysIMIanafNGWkJIfttEz_HqVlIV5_qKYVs0bzotxa8zWmmdYyLlTPBtlwp8id_Y0jG1ULimGjbc4zCb8SNAltmHcpMVBgwowprVgKJdLs_DfzNVCNRQcrvE/s400/sauropods.jpg

First.

Right then. As some of you may know, I like Dinosaurs. A lot. Unfortunately, I'm doing a degree where we don't often get to talk about them. Which is ironic, as my degree is in palaeobiology. Accordingly, I'm going to use this blog as a place to bathe in the delicious warm glow of my favourite subject, something that my university hasn't done.

I'm going to be trolling through the web in search of how environmental change has affected the beasts, looking at newspaper articles and scientific journals, in an attempt to bring in the best news and views from around the internet. I might even throw in a few of my opinions too.

http://25.media.tumblr.com/tumblr_m7a2na65Od1rsiohpo2_1280.jpg