Cloned Dinosaurs and Their Ability to Survive on Earth in the 21st Century

Abstract
In this research paper about the survivability of cloned dinosaurs a wide range of topics are covered. The standpoint of the research is that dinosaurs could not survive even if cloned in the current world. The section on oxygen concludes that the lung structure of dinosaurs in the current oxygen levels would not support a survivable species. Global temperatures currently do not support the physiology of the dinosaur species. The lack of habitat supports the thesis that dinosaurs currently couldn’t survive. Due to the current population of the world and the already starving masses and high competition for resources, dinosaurs would not have enough food to sustain life and propagate their species. Finally due to the enormous mass of the dinosaurs, the probability of evolution for them is very low leading to a dead end species.
Introduction
The following research is all about dinosaurs. It is an interesting topic that will probably have you laughing, crying, seeking out a new pet, and desiring a new career in the field of genetics just to make sure a dinosaur is actually cloned just to prove this research wrong. The problem encountered in the possibility of cloning dinosaurs is whether or not they would be able to survive on earth in its current environmental conditions. With much research and endless hours of tears over the loss of an ideal pet a decision has been reached. In the case where DNA replication is a possibility for dinosaurs, they will not be able to survive on Earth based on current global conditions. Cloning in the world today is a real possibility. A few species have been viably cloned, however nothing in mass and no humans or dinosaurs. This is possible because scientists are able to extract DNA from a large number of things both living and dead. People take many standpoints toward cloning. There are supporters of cloning. The industry of cloning could be a very lucrative industry and wealth is attractive to many. Another argument for the supporters is that cloning an extinct species would increase biodiversity. Finally for the supporters of cloning, a zoo full of extinct dinosaurs brought back through cloning would be the icing on the cake of life. Those who are against cloning are against it for an array of good reasons. The question of why it went extinct in the first place is brought up, then followed by how scary some of the dinosaurs were. They would argue there’s no space for dinosaurs on earth anymore and where would human’s keep the dinosaurs confined. Those against cloning also bring up the point that cloning is a very expensive process and the reward isn’t worth it. The probability of cloning a viable creature is very low and the money could be used toward a better cause. Finally those against cloning would ask if a cloned dinosaur could even survive on earth in it’s current state. That’s where oxygen levels become a very important aspect of survivability.
Research Analysis
A huge part of our environment includes the effects of our Earth’s atmosphere. In order to decide if a living Dinosaur would survive in today’s conditions, a research study and analysis on comparing current oxygen and atmospheric levels to that of the prehistoric era needs to be done. Presented to the audience are studies from several different sources to include data on our current lowering oxygen levels compared to the high levels of the past. We also include information on the lung structure of dinosaur species. Research explains what an impact altitude has on living species (Kerr, 2005). One source gives warning of our present-day Ice Age coming to an end within the next century. In conclusion, the research found supports the claim that dinosaurs will not survive on our Earth today due to the global effects on them.
Oxygen Levels
One source explains how the species with tolerance to a higher altitude were forced lower and closer to the Earth’s surface, causing overcrowding and later extinction (Kerr, 2005). The air became too thin for the animals to handle (Kerr, 2005). Today, oxygen is currently stable at 20% just like it was 600 million years ago, but 240 million years ago the levels dropped to 12% (Kerr, 2005). This caused animals to lose almost half of their oxygen supply (Kerr, 2005). The oxygen during the Mid-Permian time period spiked to 30%, in which case all animals could have lived and breathed without any problem at almost any altitude on Earth (Kerr, 2005). However, this is not the case now. Each species has an altitude above which it cannot survive (Kerr, 2005). For example, humans cannot live higher than 5.1 kilometers (Kerr, 2005). If humans cannot live that high, large flying dinosaurs who require even more oxygen wouldn’t be able to survive since our oxygen levels are lower than the once perfect levels in the Permian times. Another source, a book, Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere, covers various explanations about how the dinosaurs uniquely adapted so well to the continuously changing oxygen levels (Maxwell, 2006). The book also suggests, however, that our present day conditions are much harsher than what the dinosaurs have adapted to in the past and continuously getting worse (Maxwell, 2006). Only 5 million years ago the Earths oxygen levels were significantly higher than they are today (Maxwell, 2006). 78% of today’s gases is nitrogen, 21% being O2, and the remaining 1% is other gases, like carbon dioxide (Maxwell, 2006). Carbon dioxide is an important greenhouse gas that traps heat in the atmosphere and warms up the Earth (Maxwell, 2006). Humans are producing greenhouse gases at a very increasingly fast rate today and it may result in an end to our current ice age which has lasted 2.5 million years now (Maxwell, 2006). It is known that today our carbon dioxide levels are higher than ever making our earth very warm, causing a global warming effect and making our summers dreadfully hot. Only a hundred years from now will our planet have returned to its atmospheric condition in the Late Cretaceous Era (Maxwell, 2006). This is when dinosaurs were at their very largest, like the Tyrannosaurus rex and the Giganotosaurus. This is also the period when dinosaurs became extinct. If we were to clone the dinosaurs and bring them back to grow up and reproduce successfully, it would only be a matter of time before history repeated itself and the same conditions occurred. Evolution takes many years. The dinosaurs could not adapt quickly enough to protect themselves from infinite death once more.
Another article explains briefly of the lung capacity of larger dinosaurs in the Late Jurassic and Cretaceous era’s versus dinosaurs of the earlier time periods such as the Permian Era (R.M, 1997). Later dinosaurs from roughly 400 million years ago - like the giant Tyrannosaurus rex - had a large lung capacity, being able to expand their chest largely during breathing. That enabled them to take in 40 percent more air than earlier species, while earlier dinosaurs had a much smaller lung capacity (R.M, 1997).
Our last source acts as a main reason to why dinosaurs could not survive today: an article on paleontologist Jack Horner and his “Quest to Build a Dinosaur”(Lunau, 2009). Since scientists like Horner are trying to uncover DNA from dinosaurs of the later era, it is much more likely that they will uncover DNA of the larger species (Lunau, 2009). In this case, because our oxygen levels are lower than before, animals with the larger lungs will need more oxygen uptake and our earth today simply cannot support that need. Jack Horner wants to build a dinosaur within the next five years (Lunau, 2009). He’s looking into a baby t-rex skull he discovered (Lunau, 2009). Tyrannosaurus rex’s are a late dinosaur of the Jurassic and Cretaceous time period, and as discussed before, the bigger the dinosaur - the less chance of survival.
There is data regarding the analysis of today’s weather (temperature range, changes) on the survival of cloned dinosaurs. This is a comparison of the prehistoric temperature during the time of dinosaurs to our current temperature. The thesis statement stated that even if cloned dinosaurs are possible, these dinosaurs would not be able to survival in our planet with the current conditions. From the analysis of the scholarly peer reviewed (reliable) sources, then I will find back up evidences to prove that our thesis was correct. According to the majority of the data I found, most of the sources from scientists and researchers found that even if cloning dinosaurs was possible, the entire dinosaur race would just go extinct again because of our rapid changing temperature pattern and other factors associated with our current global temperature condition.
The starting point for mine research started out on the how cloned dinosaurs would not be able to survive in the current temperature conditions around the world. From there, I determined that in order for dinosaurs to survive and reproduce, suitable weather patterns as well as climate must be restored back to the old times. The topic was very hard to find, therefore, I had to make many connections with the most modern information in order to relate the sources I found. Many research studies showed that the cloned dinosaurs would reach extinction again due to the current rapid changing global temperatures. Many studies conducted on the body temperature of different organ structures of different dinosaur species. Some dinosaur species might be able to survive and adapt to the temperature changes but the majority of them would die.

The first study explained about the origin of dinosaurs from their prehistoric eggshell and that most of the dinosaurs won’t be survive the current temperature condition (Evers, 2013). This article was about the true confessions about dinosaurs that have some of the actual facts about dinosaurs that we don’t know anything about. The study in this article showed that different type of dinosaurs live in different habitats but the temperature range is not a huge difference between one another. According to scientists, global temperature was somewhat warmer in the past and it was much more consistent than the current rapid temperature change (Evers, 2013). This showed that cloned dinosaurs will have a hard time adapt to the whole changing of temperature. Not only rapid changing temperature will kill the dinosaurs but the global warming due to ice caps melting will make the earth becomes too warm for any living organisms to live on the surface (Evers, 2013). Unless the dinosaurs make adaptations but it is very unlikely because it usually takes thousands of years for evolution to take place. In this case, evolution took place and the dinosaurs became extinct so that our species can live but now we were trying to bring them back which will make it extremely hard for them to survive since we are going against evolution. Lastly, global temperature will also affect the reproduction rate of dinosaur species. Different types of dinosaur species required different but consistent type of temperature in order to reproduce. Most dinosaurs give births to eggs and in order for the eggs to survive and hatch, the suitable temperature must be present (Evers, 2013). The reproduction rate between different species of dinosaurs depends on the temperature of the environment because some dinosaurs mate when it is warm and some mate during the colder temperatures. With the rapid changing temperature range, winter and summer will be either too long or too short and it will definitely mess up different cycles of reproduction of different dinosaur species. With a rapid changing and messed up temperature pattern, reproduction processes will not take place because the little dinosaurs won’t stand a chance against this extreme temperature range. Without reproduction, dinosaur species will eventually go extinct again and everything our human race worked for would go to waste. Included in the research was a picture of our annual average temperature from 2007 which shows a lot of rapid changes from different section of the world.
Another article is about how scientists reconstructed the cloned dinosaurs and related their body physiology compositions to the global temperature change (Schilling, Jastram, Wings, Schwarz-Wings, & Issever, 2013). This study was about how scientists studied the body compositions of a dinosaur from prehistoric DNA. From the data scientists obtained, they related their findings to the survival of cloned dinosaurs to the current global temperature (Schilling et al., 2013). In order for dinosaurs to survive, their body temperature must be able to be even or warmer than their natural habitat temperature (Schilling et al., 2013). Lastly, rapid changing in global temperature will cause different chemical processes to change inside the body of these giant dinosaurs and make it extremely hard for them to adapt to the harsh environment. There is a figure included in the study showed that different species of dinosaurs can have different body temperature ranges. But most of the dinosaurs could not survive in the current temperature according to research.

Another study about how changing in global temperature can affect dinosaurs DNA (Allard, Young, & Huyen, 1995)). This study showed that not only the rapid changing global temperature can have a huge negative impact on the survival of dinosaurs but it also affect the DNA of the dinosaurs (Allard et al., 1995). Dinosaurs actually won’t be able to pass on their DNA due to the current temperature condition. If the temperature changes from cold to hot or hot to cold too fast, research showed that it will actually cause a chemical change to the DNA structure of the dinosaurs. One last study actually showed that some dinosaurs might actually survive even with the rapid temperature change in our planet (Araujo et al., 2013). This study was for us to examine the opposing viewpoint. In order for the readers to become more acceptable and believing in our stand point, we have to show them the other viewpoint saying that there are dinosaur species out there that can survive extreme climate environments. One reason why dinosaurs could not survive is because there is lack of habitat for them to live on 21st century earth. Earth has changed dramatic from 160million years ago. Paleontologists have recent evidence that Dinosaurs lived on all of the continents but since dinosaurs have been dead for over 160 million years, the earth has had extreme changes (Robert Weems 2001). The tundra is a biome where there is no tree growth because of the low temperatures and short grass seasons. Dinosaurs that lived in the tundra where consider as “artic dinosaurs” because they could survive in cold harsh temperate. Grassland is an area dominated by grass and had warmer temperatures; also found on all the continents but the Artic. Dinosaurs that live here usually were large, tall and mostly ate plants. The tropical rainforest has high average temperatures and a significant amount of rainfall. Most of your dinosaurs lived in the tropical rainforest. The desert are land that has little precipitation and little plant life because of the dry and hot weather. Dinosaurs who lived in the desert hardly survived but ate mainly what they could find. If dinosaurs were cloned in the 21st century how would they survived because the climates and habitat they once lived have changed. The habitat that was once on earth have changed, when dinosaurs lived on earth all the continents where all stuck together. As years went by the continents slowly broke apart and pieces of the continents spread across the earth. Due to 21st century global warming most of earth land has changed from ten years ago. So if earth has changed over ten year image how earth has changed over 165 million years ago. The climate, plants, and water is different from when dinosaurs use to live on earth. It might not be possible for dinosaurs to live in 21st century or if they could survive we do not know how they would react or how long they could live (Robert Weems 2001).
Research had shown that dinosaurs where fairly large and since there are many other species on Earth in the 21st century. Dinosaurs probably would kill off the human species and animals(Farlow, Dodson, & Chinsamy, 1995). There were many types of dinosaurs that live on earth and some other specie’s but mainly dinosaurs lived at that time. Theropods were the type of dinosaurs that were carnivorous (meat eaters) and mainly moved on two legs. They were the tyrannosaurus rex, velociraptor, allosaurs, spinosaurus, deinonchus, and carnotarus. Sauropods were dinosaurs that walked on all four legs, grew fairly large, and were herbivores (plant eaters). They were the Apatosaurus, Diplodocus, and Brachiosaurus. Thyreophora were dinosaurs who had armored (spikes) on their tail or back also were herbivores. They were the Stegosarurus and Ankylosarurus. Then there are the cerapods dinosaurs who had horned faces and were carnivorous. They were the Triceratops, Iguanodon, and Parasaurolophus. All the dinosaurs were fairly large and most of them were carnivorous. Since the animals that live on earth in the 21st century are fairly smaller than the dinosaur, how could both sets of animals live on earth? If dinosaurs where successful they more than likely would kill off the animals that live on present earth. There are not many large animal that live on earth now so it would be hard for them to fight for existence. Not only would the dinosaurs have to adjust living with the animals but also the humans. No one knows how human and dinosaurs interaction would be like, but if you have to guess it would deadly. Humans would not survive against the dinosaurs because how large and dangerous most of the dinosaurs are (Farlow et al., 1995).
There are facts that have be shown that Earth has a high percentage of pollution in the air and water (Rowell, 2012). With the high risk of pollution Dinosaurs could have a hard time trying to survive because of the air and water not being as fresh as it was 165 million years ago. Natural resources are how human survive every day and they are limit. Most of the trees are being cut down and now earth is filled with many building, roads, and large fields with large equipment. It would be hard for dinosaurs to adjust to all the factories and tractor trailers, which produce so much pollution. It would be very difficult for them to breathe. Many place on earth now have limit access to clean water and most of the water are bad for humans to drink. Dinosaurs would probably start dying off because there DNA is use to different atmosphere.
The availability of food for such a huge species, the dinosaurs, is a fundamental part of their survivability on earth in its current state. In the early Mesozoic era dinosaurs were not skewed towards a large species (O'Gorman & Hone, 2012). They were a much smaller species and thus required a smaller amount of food to survive individually. The carnivorous dinosaurs which commonly hunted in groups, with the exception of the infamous tyrannosaurus rex, retained their smaller size over the span of dinosaur existence due to their adequate hunting abilities (O'Gorman & Hone, 2012). However it wasn’t the same for all of the dinosaurs. The herbivorous dinosaurs gained their size through natural selection as all of the smaller herbivores became prey and only the larger ones who could fend off the carnivores survived. (O'Gorman & Hone, 2012) From this the larger herbivores were able to propagate their species until they were the dominant herbivorous species among dinosaurs.
The body size of a dinosaur is very important for determining resource use. In the late Mesozoic era the dinosaurs had evolved to a larger body size, this is the large size commonly imagined when dinosaurs are mentioned in the current day (O'Gorman & Hone, 2012). The size of an animal is directly proportional to it’s dietary intake, an animal of such a large mass would also have to consume a large mass of food in order to thrive and propagate it’s species.
The immense size of dinosaurs leads to their diet being quite large also. When compared directly with the current vertebrates on earth, the dinosaurs show a skew towards a much larger species (O'Gorman & Hone, 2012). The large size of dinosaurs leads to less energy being available for growth and reproduction unless adequate food resources are available (O'Gorman & Hone, 2012).
The availability of food for a carnivorous population of dinosaurs is readily available as the planet has an abundance of humans. A lack in their specialized diet is doubtful; however it is also doubtful that their survival would surpass that of the skilled human hunter. The availability of food for a mega herbivorous species is hard to come by. Another mega herbivore, the rhinoceros, has a very wide diet and still has trouble competing for food with other habitants of its territory (Landman, Schoeman, & Kerley, 2013).
The availability of food resources are very slim in many parts of the world. The places where food resources are not slim are also the places that are heavily populated by humans. On top of this, there is a larger population of humans now than ever before who are starving (Schram, 1993). On the sole topic of having a sufficient dietary intake for a dinosaurian species, the land would not be available. It would require huge portions of prime real estate to support the propagation of a species of dinosaurs. In most countries throughout the world, nature developments are planned to be on contaminated and polluted soils. This would lead to a contaminated food supply and possibly the inability of a successful vegetarian food supply to grow (De Lange, Lahr, Van der Pol, & Faber, 2010).
There is actually a strong correlation between a dinosaur’s physiology and it relationship to extinction. In a scientific journal written by Paul Sereno, he states how dinosaurs were slower at adapting as compared to mammals of today’s world (Sereno, 1999). This could be one of the reasons they became extinct. The mammals may have out-competed the dinosaurs (after the meteor and global climate changes). The dinosaurs are extinct now, but some organisms are still alive (e.g. mammals). Since the dinosaurs evolved so slowly, they may not have been able to co-evolve with their prey. Over a 50 million year period during the dominance of dinosaurs, only 50 new genera were created (Sereno, 1999). That is incredibly slow evolution as compared to other organisms. Some proof provided to this stance is that between the predecessor of dinosaurs and the dinosaurs rise to dominance, there is a 15 million year gap (Sereno, 1999).
With all this evidence against dinosaurs being the dominant organisms, why were they the pride and joy of this era? The answer to this is simple: They were the only type of organism around (Sereno, 1999). Building on the point of the 15 million year difference stated earlier, this means during that period they were not in competition and became dominant through simply breeding a lot over a long time. With them being the only organism, this also attributed to their already slow adaptation (Sereno, 1999).
Another point someone might say that dinosaurs are still around today. As most know, scientists have linked birds and reptiles to dinosaurs. This does not mean, however, they are dinosaurs. They evolved from dinosaurs and this was easier for them because of their body size. Dinosaurs with smaller body sizes are shown to be able to adapt and evolve faster (Sereno, 1999). This tends to be true across the board with all organisms (e.g. mammals) (Sereno, 1999).This can be explained if the think about how much more bigger animals need to survive (e.g. larger shelters and more food).
In Paul Sereno’s journal, it is stated that big dinosaurs also had less diversity (e.g. less species that are big). What can be concluded from this is that when a fatal disease starts and affects a dinosaur species with large stature, that species will be almost completely eradicated. This is because of the little amount of diversity between large dinosaurs and their lack of ability to adapt quickly.
Although the research presented above supports the idea that dinosaurs could not survive on earth, there is always the possibility that they could thrive. The pretense that adaptation is too slow for survival would quickly be discarded if just one species were produced from cloning that could survive. The species could propagate from there. The lack of habitat for a dinosaurian species would be averaged in with the rest of the competing species on the planet. Competition between species would become greater. Because of greater competition, some species may become few in number. The global temperatures and oxygen levels on earth would be easily overcome by a dinosaur species that is able to propagate its species. It only takes one genetic mutation to cause a species to be selected for in its environment. One study showed that some dinosaurs might actually survive even with the rapid temperature change in our planet (Araujo et al., 2013). The levels of oxygen on the planet in the prehistoric era were fantastic, the earth was still in its comparatively young state and the levels of pollution were all from natural phenomena. Dinosaurs were able to breathe in this pristine oxygen and were a healthy and robust species because of this. In the current times the levels of oxygen though not drastically different are full of pollution and all kinds of carcinogens. Any species on the planet that breaths oxygen is at a disadvantage compared to the dinosaurs which previously ruled the earth in the prehistoric era. The oxygen levels millions of years ago were indeed fantastic, however the climate was perfect to facilitate the creation of life and also to sustain that creation of life. The climate did not change so rapidly as it does currently. The rapid changes in our current environment are not conducive to a long life for those who are caught in the negative changes. The climate in the prehistoric era, though not completely certain of what it is, was better and most probably more stable than it is in the current era. This era in 2014 is not a time when bringing about a new species is a fantastic idea. The species would not only have to overcome the oxygen levels and pollution, but it would also have to overcome the rapid changes in climate which would be relatively difficult for a species with no large gene pool to draw species stability from.
The lack of habitat can also be drawn from the lack of oxygen and the rapid changes in temperature. Pollution also has a large deal to do with the lack of habitat. Any land that is available to the new dinosaur species would not be free of pollution. It would not have pristine oxygen to breath and the climate would most probably change so rapidly that the species would be wiped out within a quick matter of time.
The adaptation of dinosaurs would be a good way for them to overcome any of these obstacles. After all that is how every species has continued to live on and on in this great world. However because the dinosaur is such a huge species it would have the most difficult time adapting to a new world. The species is so large and any small mutation would most likely not be sufficient to cause an adaptation sufficient to allow the species to continue to live and propagate.
In the instance of the propagation of species they would still need the food to be available for consumption in order to have the energy to reproduce. With the limited land available due to the lack of environment and the lack of oxygen, the probability of food being available is very low. On that same note any food that was previously available would have to survive the rapidly changing environment. This brings along the caveat that the food that does survive will also have to be readily edible for the dinosaurian species. All of these things together lead to the conclusion that the dinosaurs, if cloned, would not be able to survive on the earth in it’s current conditions.

The fun and thematically popular idea of bringing back viable dinosaurs is not scientifically possible. The oxygen levels on earth that could have supported dinosaurian life are simply too low and creatures of such great magnitude would not intake enough oxygen to sustain life. The rapidly changing temperatures and climate of the planet in its current state are not suitable for sustained life of dinosaurs. The availability of food for a creature of such great magnitude is simply not available without intense competition. Large dinosaurs are not able to quickly adapt to environmental changes and thus if cloned will not be able to propagate a viable species.
References
Allard, M. W., Young, D., & Huyen, Y. (1995). Detecting dinosaur DNA. Science (New York, N.Y.), 268(5214), 1192; author reply 1194.
Araujo, R., Castanhinha, R., Martins, R. M. S., Mateus, O., Hendrickx, C., Beckmann, F., . . . Alves, L. C. (2013). Filling the gaps of dinosaur eggshell phylogeny: Late Jurassic Theropod clutch with embryos from Portugal. Scientific Reports, 3. doi: 10.1038/srep01924
De Lange, Hendrika J., Lahr, Joost, Van der Pol, Joost J. C., & Faber, Jack H. (2010). Ecological vulnerability in wildlife: Application of a species-ranking method to food chains and habitats. Environmental Toxicology & Chemistry, 29(12), 2875-2880. doi: 10.1002/etc.336
Evers, J. L. H. (2013). Confessions of a dinosaur. Hum Reprod, 28(5), 1152-1154. doi: 10.1093/humrep/det075
Farlow, James O., Dodson, Peter, & Chinsamy, Anusuya. (1995). Dinosaur Biology. Annual Review of Ecology and Systematics, 26, 445-471. doi: 10.2307/2097215
Kerr, ñRichard A. (2005). Gasping for Air in the Permian. Science Now, 1-2.
Landman, Marietjie, Schoeman, David S., & Kerley, Graham I. H. (2013). Shift in Black Rhinoceros Diet in the Presence of Elephant: Evidence for Competition? PLoS ONE, 8(7), 1-8. doi: 10.1371/journal.pone.0069771
Lunau, Kate. (2009). THE QUEST TO BUILD A DINOSAUR. (Cover story). Maclean's, 122(32), 40-43.
Maxwell, Gloria. (2006). Out of Thin Air: Dinosaurs, Birds, and Earth's Ancient Atmosphere. Library Journal, 131(14), 174-174.
O'Gorman, Eoin J., & Hone, David W. E. (2012). Body Size Distribution of the Dinosaurs. PLoS ONE, 7(12), 1-12. doi: 10.1371/journal.pone.0051925
R.M. (1997). How much air could a dinosaur breathe? Science News, 152(18), 287.
Robert Weems , Ronald Litwin , Thomas R. Holtz, Jr (2001). Where did Dinosaurs live? Dinosaurs Fact and Fiction 1.
Rowell, Arden. (2012). Allocating Pollution. The University of Chicago Law Review, 79(3), 985-1049. doi: 10.2307/23317729
Schilling, René, Jastram, Benjamin, Wings, Oliver, Schwarz-Wings, Daniela, & Issever, Ahi Sema. (2013). Reviving the Dinosaur: Virtual Reconstruction and Three-dimensional Printing of a Dinosaur Vertebra. Radiology, 130666-130666.
Schram, Sandy. (1993). Hunger 1993 Uprooted People: Third Annual Report on the State of World Hunger. American Journal of Economics & Sociology, 52(4), 491.
Sereno, Paul C. (1999). The Evolution of Dinosaurs. Science(5423), 2137. doi: 10.2307/2898419

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