Seventh.

This recent posts have focused on the adaptability of dinosaurs to survive climate change; this one will examine how it could have wiped them out. The Deccan Traps, India, was an area of intense volcanism towards the end of the Cretaceous, caused by the northward movement of India over the Reunion hotspot. Covering over 512000 km² today after erosion, the original lava flows would have spanned nearly three times as much (Keller, 2011). Operating over one million years, three distinct phases of volcanicity can be attributed to the flow, the largest being the second phase, right at the K/T boundary (Keller, 2011) 

The problem with associating the Deccan Traps to the end Cretaceous mass extinction is the fact that there are recovery periods between each phase, as well as the lack of significant marine microfossils interbedded within the traps, as they are a good indicator of mass extinction events (Keller, 2011).  However, comprehensive data collection at the volcanism site by Keller et al. (2011) has yielded more information on the exact nature of the event.

Microfossils were found in quarries along the K/T boundary, and showed the devastating impact of the volcanism of these tiny marine organisms:

 

The fossils found here were concordant with fossils found at other localities with known volcanicity, showing a high-stress low-diversity assemblage (Keller, 2011), in what is known as the "Lilliput effect". In addition, gas concentrations were calculated, after being preserved in rare bubbles within the rock. The concentrations of carbon and sulphur dioxide was beyond any anthropogenic induced change seen today, whilst evidence of a 'cooling' stage would have increased weathering, thus compounding the adverse effect of the gases. Keller (2011) writes:

Relating to dinosaurs, Keller (2009) wrote in an earlier paper how the last known remains of the reptiles are found before the significant lava flows at the K/T boundary, between the first and second phase, and show no signs of recovery after. It is plausible, therefore, that the Deccan traps had some effect on the giant reptiles. The theory of mass volcanism should not be disregarded in favour for the Meteor Impact theory, rather the meteor was the final straw in an already stressed environment, thanks to the volcanism. 

  

http://filebox.vt.edu/artsci/geology/mclean/Dinosaur_Volcano_Extinction/media/cretdawS.gif

http://www.science-story.com/images/deccan-traps.jpg

Keller G, Sahni A and Bajpai S 2009 Deccan volcanism, the KT mass extinction and dinosaurs; J. Biosci. 34 709–728

Keller et al. 2011.Deccan Volcanism Linked to the Cretaceous-Tertiary Boundary Mass Extinction: New Evidence from ONGC Wells in the Krishna-Godavari Basin. JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.78, November 2011, pp.399-428 

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 

Fifth.

Apologies for the absence, a few projects cropped up that needed my attention. This blog will be looking at how fluctuations in atmospheric oxygen levels may have had an influence on evolution, which caught my attention thanks to an article written by Berner and his colleagues (2009):

 Throughout history there have been fluctuations in global oxygen levels, whose cause can be attributed to tectonic activity capturing carbon dioxide into underground carbon stores, volcanism spewing out a cocktail of gases into the atmosphere and, perhaps fundamentally, the evolution of photosynthesising organisms, who produce oxygen as a by product. Thus, organisms have to adapt accordingly, in order to maintain and regulate their environment in what is known as the 'Gaia Hypothesis'. 

 The above graph comes from Berner et al's (2009) article, showing atmospheric oxygen levels during the Phanerozoic, noting that several extinction events coincide with decreasing oxygen levels, such as at intervals 5 (Devonian), 9 (Permain-Triassic) and 11 (Triassic-Jurassic) on the graph. Berner (2009) denotes four major events relating to evolution and oxygen:

1. The origin of the first animal body plans coincides with an increase in oxygen (interval 1).
2. Two independent phases of high oxygen levels relate to the conquest of animals on to land, interval 4 showing the first of these conquests, mainly achieved by arthropods, and interval 7, which included the vertebrates.
3. The all time oxygen high during the Carboniferous and Permain (8) may have caused gigantism in several arthropod groups including the dragonflies and millipedes, whilst an overall increase in body size is seen in many vertebrate groups. 
4. Interval 12 may have caused the increase in mammalian body size during the tertiary.

However, the mechanisms of these points are unclear, however the presence of high oxygen levels is seen to influence size in trout (Dabrowski, 2004), and alligators (VandenBrooks, 2007).

The decrease in atmospheric oxygen during the late Triassic (interval 10), coincides with the rapid diversification of dinosaurs. This may have been due to a novel mechanism used by these organisms to extract oxygen in low oxygen conditions, and is retained by birds today due to its usefulness during high altitude flight. Known as the pulmonary air sac system, fossilised dinosaur bones are seen to have air filled spaces, where the bone has been invaded by the aforementioned system (O'Connor, 2005). Essentially, these air sacs means that inhaled air in effectively passed into the lungs twice via a bellow system, extracting as much oxygen as possible from one breath. Thus, dinosaurs had a respiratory advantage compared to other terrestrial organisms at the time, causing their rise and diversification as dominant land animal for 150 million years. 

Berner et al, 2009- http://webh01.ua.ac.be/funmorph/raoul/fylsyst/Berner2006.pdf

K. Dabrowski, K. J. Lee, L. Guz, V. Verlhac, J. Gabaudan, Aquaculture 233,383 (2004). 

J. M. VandenBrooks, thesis, Yale University (2007). 

Patrick M. O'Connor & Leon P. A. M. Claessens (2005) Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs Nature 436, 253-256

http://michigantoday.umich.edu/2008/10/aero1-lg.jpg