Twelfth.

Returning to a post I made about the Permian/Triassic mass extinction and its effect on dinosaur evolution, I recently came across this article:

The end Triassic extinction coincided with the rise of the Dinosaurs. The world was different back then, having just suffered the worst extinction in the history of the living world, and the continents were amassed into one single supercontinent, Pangea. Jessica Whiteside and her team (2010) used fossil evidence and the carbon signature found in fossil leaves and wood deposited in lake sediments containing basalts, which indicated volcanic activity, to construct a climate record marking at the Triassic/Jurassic boundary. 

The researchers proposed that a large spike in carbon dioxide levels in the air due to volcanism resulted in half of land plants going extinct, whilst also marking the end of the Triassic. The volcanism is thought to have originated from the drifting North American and African plates, leading to 9 million square kilometres of lava being generated. Pollen counts and C12 and C13 isotope concentrations showed just how badly this effected the plant life in terrestrial environments. The rise in carbon dioxide concentrations also destroyed crurotarsan populations, cousins to the crocodiles, that competed for terrestrial dominance with the early dinosaurs.  

Crurotarsans

Freed from their crurotarsan competitors, the carnivorous theropod dinosaurs dramatically increased in number (see Olsen, 2002, who documented this rise). Whether this rise was due to adaptive evolution or just luck, is still unknown, and many never be discovered, but once again shows that climate change had its hand in creating the most dominant species the world has seen. 

Jessica H. Whiteside, Paul E. Olsen, Timothy Eglinton, Michael E. Brookfield, and Raymond N. Sambrotto. (2010) Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction. Proceedings of the National Academy of Sciences

Eleventh.

Throughout these blogs I have tried to incorporate paleoclimatology with anatomy and physiology, in an attempt to see how the effects of climate fluctuations causes species to adapt (or in some cases, go extinct) to these new conditions. The most interesting fossil finds of the last decade and a half are the fossil feathered dinosaurs, especially from China, and I have touched on this subject a few weeks ago with my article on Yutyrannus. For this post we will be returning to China, with an article that enhances my aforementioned post on the largest feathered theropod and its implications on Cretaceous climate.

The Jehol Biota, named after a province in China, is arguably one of the finest fossil deposits on the planet, with immaculately preserved feathered dinosaurs, plants and invertebrates all being found, shedding light on the Early Cretaceous ecosystem. Thanks to such pristine preservation, a large team from France, China, Thailand and Japan examined the isotope concentrations in fossil structures such as teeth and bone. Air temperature alters the amount of certain oxygen isotopes contained in rainwater, which is drunk by animals. This "record" is then passed on during growth during bone and tooth formation, which is then preserved in the fossil record. They assigned the differences in isotope concentrations between dinosaur taxa to differences in water strategies, diet and microhabitat, as such differences are expected.  

What they found is mirrored in the Yutyrannus post a few weeks back. The idea of a entirely warm Cretaceous era was banished in favour of a new idea that during some stages, the climate was much like modern day climates at the same latitudes: a cool, temperate climate with harsh winters. This would have forced the ectothermic turtles and crocodiles, for example, to hibernate. Amoit (2011), lead author of the paper, wanted to make the appearance of feathers on dinosaurs clear: "These results do not prove in any way that feathers appeared because of their insulating characteristics. They show that feathers would have given the dinosaurs of the Jehol fauna a physiological advantage over their fellow animals with scales". 

Jehol Dinosaurians, characterised by feathers 

Its is therefore necessary, therefore, to continue research in these Chinese provinces, and perhaps look for feathered dinosaurs in Cretaceous rocks before this "cool" period set in, and examine the oxygen isotopes. If feathers are present in a large number of species, as they are in the Jehol rocks, even in warmer climes, we could predict that feathers were indeed used for reasons other than insulation. However, should the appearance of feathered species coincide with the decreasing temperatures, then it is understandable to reject Amoit's claim.

R. Amiot, X. Wang, Z. Zhou, X. Wang, E. Buffetaut, C. Lecuyer, Z. Ding, F. Fluteau, T. Hibino, N. Kusuhashi, J. Mo, V. Suteethorn, Y. Wang, X. Xu, F. Zhang. Oxygen isotopes of East Asian dinosaurs reveal exceptionally cold Early Cretaceous climates. Proceedings of the National Academy of Sciences, 2011
http://www.sciencedaily.com/releases/2011/03/110311173104.htm
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJ9aXdk_3_QAHSLqNb6HrxBTfYRRJ0119nOblB8ubbXXgMEnCAvxF65ReU6FWuwQKN6zbDB4eQt5z3dNP8czhAE78hc5815vpY63CtNMPfUFYObEYkA8OjCvTtN9NMI-bomXMMjQmMxM4A/s1600/Dinosaurs+like+Cat.jpg

Tenth.

The Great Dying. The end Permian extinction was the largest known extinction event in Earth's history: 90% of marine fauna and 70% of terrestrial organisms did not make it into the Mesozoic. However, this extinction directly precedes the rise of the dinosaurs. It is thought that volcanism at the Siberian Traps played a key role in this event. However, new research puts into perspective exactly how devastating the aftermath of the extinction was for life on earth, as well as showing how adaptable the first dinosaurs were, evolving from the ashes of a catastrophic event. 

Two papers caught my attention regarding the subject, both siting climate as the reason it took life several millions of years to recover. The first, in my opinion, is absolutely mind blowing in regards to early Triassic climate. After a mass extinction, the fossil record always hints at a "dead zone", where species are not seen for thousands of years. After the P/T extinction, species were not seen for 5 million. 

Lead author on this project, Yadong Sun, puts this down to extreme temperature, especially around the tropics: ocean surface temperatures of 40 degrees, and amazingly, air temperatures of up to SIXTY degrees. "Global warming has long been linked to the end-Permian mass extinction, but this study is the first to show extreme temperatures kept life from re-starting in Equatorial latitudes for millions of years", says Sun. Photosynthesis stops, and terrestrial animals cannot maintain the high metabolic costs of keeping cool. The lack of photosynthesising plants, which had trouble recovering from the extinction, meant a breakdown in global carbon recycling, thus causing an unchecked increase in greenhouse gases, and hence temperature. This data was collected by examining oxygen isotopes in conodont teeth, which are temperature controlled.

An article posted only a few days later seemed to enhance Sun and his team's findings. Sedlacek and Saltzman, of Ohio State University, examined the chemical composition of sedimentary rocks laid down at the extinction event. They found that as a result of volcanism at the time of the great dying, large amounts of the Earth's surface was being weathered by greenhouse gases, as well as deposition of vast stretches of lava, chemically altering the Earth's climate. The air was full of carbon dioxide, and oceans chocked with sediment. "It was a game-changer, biologically. Fish would have had silt in their gills, coral reefs would have been buried -- as far as we can tell, the things that truly thrived in the ocean during that time were microbes," according to Sedlacek. 

Nyasasaurus 

These findings come with the exciting, paleobiologically speaking, discovery of the oldest known dinosaur, Nyasasaurus, pushing back the date of the first dinosaurians by over 10 million years, into the middle Triassic. How the archosaurs, the group dinosaurs radiated from, not only survived the P/T extinction, and then endured the recovery hell that made life almost impossible, must go down as one of the greatest feats in nature.  

Yadong Sun, Michael M. Joachimski, Paul B. Wignall, Chunbo Yan, Yanlong Chen, Haishui Jiang, Lina Wang, and Xulong Lai. Lethally Hot Temperatures During the Early Triassic Greenhouse. Science, 2012; 338 (6105): 366-370 

http://www.sciencedaily.com/releases/2012/10/121018141844.htm

http://www.sciencedaily.com/releases/2012/11/121105081238.htm

http://i.livescience.com/images/i/000/034/065/iFF/nyasasaurus-121204.jpg?1354662975

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.  

Eighth.

While searching for some information on the idea that climate and the presence of feathers on dinosaurs are related, I came across this video:

It was a short video with in fact very little information what so ever. The article published in nature however, was much more interesting. Yutyrannus was a relative of its well known cousin Tyrannosaurus rex but with one distinctive honour: it is the largest known feathered dinosaur.

At thirty feet long and just shy of 1.5 tonnes, Yutyrannus was covered in downy feathers similar to those found on juvenile birds, clearly making flight impossible (in addition to the fact that it had tiny arms and insufficient muscle mass on its chest to even dream of generating uplift). Insulation, therefore, seems a more plausible idea. Indeed, the fossil finds indicate Yutyrannus live during the middle of the early Cretaceous, with known drops in temperature. Having feathers means that this predator could stay active for longer despite the cooler temperatures.

Furthermore, new research on Yutyrannus' relatives, the feathered plant-eating Ornithomimosaurs, Oviraptosaurs and Therizinosaurs, indicates the role of climate in body size. Being herbivorous, it was always assumed bigger meant better; large size means larger guts, useful for extracting the maximum possible calories from the nutrient poor plants they eat. And in general, this held true: these dinosaurs did display an average increase in size through time. 

Beipiaosaurus, a Therizinosaur

However, when evolutionary models were applied to the fossil data to test whether natural selection was driving them to get bigger, they discovered that these theropods were actually experimenting with body size, some getting bigger while others were getting smaller. "Results of our study don't rule out diet as affecting body mass, but do seem to indicate that fluctuating environmental conditions over time were trumping the benefit of becoming a giant," according to Zanno, who lead the research. When the climate was right, these dinosaurs could get very large, however, factors like competition, food availability and most of all climate change, meant that in some cases, bigger was not always better. 

  

http://www.sciencedaily.com/releases/2012/04/120405133401.htm

http://www.sciencedaily.com/releases/2012/11/121128093254.htm

http://wodumedia.com/wp-content/uploads/2012/10/Beipiaosaurus.jpg

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