WILL DINOSAURS RETURN?

WILL DINOSAURS RETURN? An Investigation into the evolution of dinosaurs and their modern descendants By: Claire Qiu, Cindy Wang, Emily Yeung, Cynthia Zhao *Recommended to view in full screen

Premise • THE QUESTION: • Would a 2-degree Celsius rise in Earth’s global temperature prompt the gradual return of dinosaurs? • OUR ANSWER: • No. And here’s why:

The Extinction of Dinosaurs • Around 65 million years ago, the last non-avian dinosaur became extinct in a mass-extinction called the Cretaceous-Paleogene Extinction, also known as the K-T Extinction. • It was the second largest mass-extinction of all. Approximately 65-70% of all species that were living during that time were wiped out. • Since so many species were wiped out, it was possible that the dinosaurs ran out of food sources. However, the exact cause and length of this extinction is not known, so there are several theories each with supporting evidence.

Volcanism: A probable answer to the mass extinction of the dinosaurs At an adequately grand and swift extent, volcanism alone can be the catalyst of extinctions. Thus, it is quite possible that these fire-breathing dragons of the earth could have killed off the dinosaurs over time. This theory indicates that volcanism slowly killed off the dinosaurs over a span of several million years. Through fossilised evidence, scientists are quite convinced that there was increased volcanism nearing the end of the Cretaceous period. It is postulated that increased volcanic activity could have possibly created sufficient amounts of dust and soot to obstruct sunlight; that alone triggers climate change. Volcanic activity also releases poisonous materials containing noxious gases such as sulphur, which can in turn pollute ecological systems internationally via acid rain. There are theories as to why volcanism was so active near the end of the Cretaceous period. One cause may be the significant alterations of the positions of the plate tectonics occurring during the K-T boundary. Continental drift alone caused the oceans to experience regression, resulting in a less mild climate. Some dinosaurs may have been sensitive to such changes, and their populations may have been impacted, but it is more probable that the volcanism, acting as a result of continental drift, affected the dinosaurs by a more substantial amount. Another theory, namely “Antipodal Volcanism”, stresses that volcanism can be caused by seismic energy radiating from oceanic large-body impact sites, and that this seismic energy is focussed at areas antipodal from the initial impact site. The seismic energy would then leave a path of destruction through the Earth, starting from its depth and quickly travelling to the surface.

…continued There is quite a bit of evidence that supports this theory. In the fossil records, the sediments containing iridium--which signifies an asteroid impact--showed up after the extinction occurred. Arguably, it is impossible for a meteorite impact to produce sufficient amounts of poisonous sulphur and carbon dioxide gas to correspond with the level seen within the rocks. The fossil record also contained plankton species, and layer after lava layer, the plankton species got fewer, smaller, and retained less elaborate shells. The majority of the species died off gradually. The so-called “sea cockroach” was the Guembilitria, which is a tough species of plankton. When volcanoes erupted, their sulphur, in the form of acid rain, fell into the ocean and chemically bound with calcium. Many species died as a result of the unavailable calcium. With its simple exoskeleton, Guembilitria was able to thrive in the wake of disaster because it did not need the calcium other sea creatures needed to build their shells and skeletons. As a result, the amount of Guembilitria fossils exploded to constitute 80% and 98% of the fossils within fossil records. This evidence is the most prominent in the fossil records and sediments the Deccan Traps of India. However, there are still doubts about this theory because it cannot be proven unless knowledge of the “volcanic tolerance” of the dinosaurs is obtained. Also, it is important that the timing of the eruptions is known, because if the eruptions in fact occurred before the time of the mass extinction, then the dinosaurs were not affected. The cause of this mass extinction has yet to be figured out.

Fossil Evidence From India

Asteroid Impact An asteroid impact around 66 million years ago in the Yucatan Peninsula (Mexico) is theorized to have caused devastating consequences to Earth, including pressure waves, global wildfires, tsunamis, and a “wave” of molten rock re-entering the atmosphere. Material remaining in the atmosphere, blocking solar radiation, would have drastically decreased the temperature, and killed much of the plant life. The origin of this theory comes from a discovery of iridium dating back to the end of the Cretaceous. Iridium is rare on Earth, but common from rocks in space. Notably, this impact may have occurred alongside volcanic eruptions, and is likely not the only cause of extinction. Asteroids falling on Earth can create a big blast. When the materials fall back on earth as ballistic debris, it can possibly generate radiant heat energy.

The Greenhouse Effect The greenhouse effect is a result of various other theories. In the Asteroid Impact theory, global wildfires and molten rock release many harmful gases into the atmosphere. Volcanoes also release toxic gases that pollute the environment. Carbon dioxide gas is released into the atmosphere and is slowly building up. Moreover, the dust, smoke, and other impacts make it hard for sunlight to get through. Land plants and algal planktons cannot photosynthesize. The mass-extinction of plants cut down oxygen levels and raise carbon dioxide levels. The loss of sunshine for a long period of time and the presence of dust particles in the air soon caused a decrease in temperature. The greenhouse effect comes into action. The global warming process would kill any species that is very sensitive to temperature and environment. The herbivores lost a major food source. The carnivores, who feed on herbivores, also lost their food sources. The dinosaurs, being at the top of the food chain, is greatly affected by the loss of species. Once temperature rises to a certain point, it becomes unbearable for certain species. The high temperature lasts for a thousand years or more.

The Geneticist’s Justifications • SHORT INTRO ON EVOLUTION: • Evolution is almost completely random, except for the fact that some factors encourage evolution. • Some of these factors may include climate, competition, and availability of food. (The reason is because of independent assortment and crossovers which are also random, and increases complexity.) • The descendent and the ancestor can technically co-exist because there might be organisms uninvolved in the evolution.

Genetic Randomness • Phenotypic and genotypic variance is due to genetic variance in a population. • Genetic variation allows an increase or decrease in the frequency of alleles • Genetic variation can be caused by mutation, (which causes a whole new allele to be formed in the population) random mating, random fertilization, crossing over, and independent assortment. • These factors allow the offspring of organisms to be different from their parents. Phenotypic variance has a great impact on evolution. • Neutral alleles are not eliminated nor selected, so they simply remain in the population. • Geographic variation is when the species’ population lives in different environments, and they may adapt differently. (For example, continental drift may have caused dinosaurs to adapt accordingly) • New genetic variation is created every generation, so a population with higher reproduction rates may have higher genetic variance. • However, all of these events happen at random, and so does natural selection and genetic drift, which may decrease genetic variation. • The ways genes realign themselves in the offspring is unpredictable, and therefore in small populations gene frequencies can fluctuate. • Even though it is very hard to, it is possible to eliminate a gene completely.

Dinosaurs: A history • Dinosaurs likely evolved from a family called the archosaurs, which are primitive reptiles. • Though these archosaurs have many similar characteristics with the dinosaurs, archosaurswere much smaller than dinosaurs. There are theories that state that dinosaurs evolved from a genus called lagosuchus, a fast and tiny reptile. • In the Devonian Period, some of the marine animals moved onto land due to abundant food sources. In the Carboniferous Period, tetrapods appeared, and some of the larger amphibians evolved. • Reptiles evolved from amphibians and later split evolutionary paths. This is why amphibians and reptiles both exist. • Later, a great evolutionary step occurred with the development of amniotes, animals laying shelled eggs, allowing them to reproduce out of water.

…continued • During the Permian, reptiles populated the land. • At the end of Permian, a mass extinction wiped out 75% of all tetrapod families. • This mass extinction marked the end of the Paleozoic Era. Mesozoic Era began with the Triassic Period, when Pangaea existed. • As much of the land was far from the water, the climate was hot, arid and dry. • In the early Triassic, the land was dominated by archosaurs, the dinosaurs’ ancestors. Dinosaurs appeared later, in the late Triassic. • They may have taken advantage of the vacant land left by the extinct animals from the mass extinction. • In the Jurassic Period, Pangaea broke apart. • Mammal-like reptiles were extinct at the Triassic-Jurassic boundary, which allowed dinosaurs to spread even faster. • The mild Jurassic Period allowed the dinosaurs to grow bigger in size. • One of those called the Brachiosaurus, a sauropod, had a long neck and elongated front limbs, which allowed the dinosaur to reach higher vegetation. • In the Cretaceous, separated landmasses allowed dinosaurs to evolve separately from each other. • Larger sauropods were replaced by smaller herbivorous ornithopods. This was perhaps due to the adaption of vegetation in the area. In the late Cretaceous, Tyrannosaurus appeared.

Cladogram of Dinosaur Evolution

Early Dinosaurs • The earliest dinosaurs were all bipeds, walking on two legs, but then they got too large to be supported by only two legs. • This allowed them to move faster and further without stopping. • On the other hand, lizards and crocodiles found it hard to breathe and run at the same time because their bodies undulate from side to side. • Bipedal dinosaurs could probably run for longer periods of times. • This was very useful when they are attacked or to catch prey for carnivorous dinosaurs. • The large sauropods had to walk on four legs because of the large stomach they have to digest tough plants. • Also, the head size of dinosaurs differed. In order to balance properly, many larger dinosaurs turned to walking on four legs. • Dinosaurs are better balanced than humans because they had a thick tail to keep them stable, whereas humans had to react constantly to sensory stimulus to keep them standing upright.

Divergence • The dinosaurs themselves had little similarities except for the fact that they are all classified as dinosaurs. • Their diets were very different as well. Few amounts of dinosaurs interbred and traits were not shared. • Therefore evolution could only occur in a specific species and not a group of species. • However, when mutations build up, a new species emerge. Because of the limits for food, the diets for dinosaurs changed. • In order to fulfill their hunger, the carnivorous dinosaurs had to be big and strong to capture prey. • A portion of the small reptiles, depending on where they lived and the availability of food, evolved to grow in size. • The scarce food source also caused the herbivorous dinosaurs to grow taller, so they could reach higher trees and eat the leaves there. • Later, to avoid being eaten, some dinosaurs evolved to have wings on the front limbs. • These avian dinosaurs could then travel easily without being eaten and had access to more food sources. • Some of these dinosaurs may have been survivors of the cretaceous mass extinction and became ancestors of birds. • Some feathered dinosaurs evolved possibly out of warmth in a cold weather.

A Cladogram:

The Paleontologist’s Predictions • WHAT FOSSILS PROVIDE US: • By looking at fossils, one can determine the growth patterns of ancient organisms. • Should there be naturally-induced damage on the fossils, it can give evidence of the forms of other ancient organisms and, thus, this proof can help scientists formulate hypotheses and understand the evolutionary processes of the prehistoric times.

Transitions • “Transitional forms” are fossils that show the stage(s) of evolution between a defined ancestral organism and a present-day organism. • Finding transitional forms would help us understand the evolutionary paths of organisms more clearly.

…continued • Homology in corresponding "parts" in fossils indicate the roots of the evolutionary paths of various organisms, often illustrating the fact that there is a common ancestor

A Story of the Past • Comparing fossil ecosystems help scientists understand the climates of the past • However, such studies are made on the basis that the climate "comfort zone" of the organisms studied is the same today as it was in the past.

…continued • Knowing about the climates of prehistoric times allows scientists to analyse the changes that occurred in correspondence to the changes of the climate. • That way, if the Earth were to warm by 2 degrees Celsius, scientists can make a general hypothesis on whether or not dinosaurs will be reborn, as they have the background information from the fossil records; the records would indicate the approximate time it takes for organisms to adapt to climate change and other conditions by using some type of atomic dating. • The study of fossil soils allows scientists to estimate how the conditions were in the past (such as precipitation levels and seasonal patterns), and if the modern climate starts displaying such patterns, paleontologists can better understand potential consequences.

Rare remnants? • Many have had high hopes of extracting some sort of DNA from prehistoric fossils, but it is close to impossible. • DNA degrades very quickly, and even within a well-preserved fossil covered in resin. • Scarce DNA samples can only be available in "younger" fossils (e.g. Neanderthal Man) • Even if the organism was trapped in amber, which can dehydrate and preserve the tissues of the organism, the DNA won't survive if the fossil is too ancient. • Also, a lot of the DNA that was presumably "found" was actually contaminations (half-life of DNA is 521 years under average local temperature) • However, conserving the tissues alone is important, as it can be used to study the anatomy, which would help paleontologists gain a significant knowledge of the environment and how the organism adapted to it.

The Physiologist’s findings • DINOSAURS AND AVIANS: • Dinosaurs’ closest relatives are birds. • There’s plenty of evidence for this link:

…continued • One of the major proteins found in bones is collagen. • This protein could be extracted from dinosaur bones to examine DNA. • Collagen is very stable and is chemically modified by the body. It is easily distinguished and does not mutate as often. • Scientists can now add something called EDTA that can turn bone fossils back into bones by demineralizing it. • Dinosaur gene samples of different stages of development are needed to find out the different proteins. • Genes that code for appearance and where and when to make proteins would not be available from protein data. • Moreover, genes are turned on and off from time to time. • From our limited knowledge, it is hard to tell exactly when the dinosaurs evolved and who are their ancestors and descendents. • When scientists added EDTA to a well-preserved T. Rex bone, they found traces of collagen, very similar to chicken’s, in it. The collagen sample was also somewhat related to the frog and the newt. • There are also theories that alligators and crocodiles are very much related to dinosaurs as well, as they are the living archosaurs.

Structural similarities • Bone structures that dinosaurs had included backward pointed hips, which is coincidentally the same as modern birds today. • Bipedal dinosaurs share the same type of feet as birds, with three toes forward, and one toe back, as well as the similar nails and claw structure.

…continued • Dinosaurs also share the same neck and shoulder bone structure with the birds, as both have ‘S’ shaped necks along a long shoulder bone.

…continued • Most carnivorous dinosaurs used a breathing systems of bellows, which included the usage of air sacs. These air sacs allow oxygen to be pumped through the lungs of the creatures. The only creatures that breathe in this manner are birds. • Airborne dinosaurs, which evolved later on, such as the Archaeopteryx, had feathers, which helped with its flying abilities. This is one of the biggest traits that are shared with the modern birds.

…continued • The pelvic bones of the dinosaurs allow the saurischian and ornithisciandinosaurs to be distinguished from one another. • Saurischianshave lizard-like pelvic bones, whereas the ornithiscian dinosaurs have bird-like pelvic bones. • Like the lizards, the pelvic bones of the saurischians are oriented more horizontally and pointed forwards • The pelvic bones of the ornithischians are instead pointed down and towards their tails, like those of birds. • In fact, theropods wound up evolving into the birds that we see nowadays.

Senses of Smell • The brains of dinosaurs have very large olfactory lobes: • This indicates their great sense of smell. • Most birds today have evolved to have a very poor sense of smell. • There are a few exceptions of a bird species that have nearly the same sense of smells as these dinosaurs • This includes the Kiwi birds and Turkey Vultures, both which are known as ‘endangered species’. • Being extremely sensitive to the scents in their environments, these two bird species have found it difficult to maintain their good senses of smell which is crucial in their survival. • Kiwi birds and Turkey Vultures are supposedly the only birds that hunt with their sense of smell, with kiwis being omnivores, and the Turkey Vultures being carnivores. Due to high levels of pollution, olfactory lobe sensitivity of these birds have significantly diminished. • There are multiple carnivorous and herbivorous dinosaurs in the Mesozoic Period, known as the Cathemeral dinosaurs which were active during both day and night, and would hunt for its prey or food during the nighttime using their sense of smell rather than their sense of sight.

Reduced Resources • In our current society, much of the world’s vegetation has been reduced. • Large trees have been chopped down for lumber and construction uses • Low plants and shrubs have been uprooted to make room for urbanization and agricultural purposes • Most herbivorous dinosaurs either have evolved to have elongated necks to reach high foliage in trees, or to have turtle-like beaks which allows these dinosaurs to close crop the lower plants with their mouths • If there were not to be enough food to sustain such herbivorous dinosaurs, there would naturally be lacking in food for the carnivorous dinosaurs, as carnivorous dinosaurs tend to feed on these herbivorous dinosaurs.

Words of Note • The Geneticist’s: • At this moment humans have already manipulated the environment to a noticeable degree. • The biosphere cannot support any more organisms. • Relatives of dinosaurs nowadays are evolved to fit in their environment perfectly. • They do not lack food sources in particular, which would otherwise prompt some sort of change. • Evolution generally happens through a long period of time, and through many generations. • This is why people today seldom find new species. • Even if dinosaurs do rise up again due to random gene shuffling, the environment may not support them. • There is also very little chance that the dinosaurs evolved today will even be similar to the dinosaurs back then, and they might not even be dinosaurs at all due to the different ways of evolving and difference in gene pool.

The Paleontologist’s: • Looking at the evolutionary path of the fossils of dinosaurs and its descendants, it is not possible for dinosaurs to reemerge as a species after global warming persists. • The shrinking in body size was a trend, starting from dinosaur fossils to the fossils of its descendants today. • It is unlikely that in such a short time--as global warming is happening quicker than ever--descendants of the dinosaurs will increase in size, to the extent of being classified as dinosaurs once more.

The Physiologist’s: • If these dinosaurs were put into the current environment where pollution is overwhelming in the air, this will stunt the sense of smell of the dinosaurs, and make it harder for them to hunt. Nocturnal dinosaurs would be particularly affected. • If the dinosaurs were to instead feast on other smaller, current species, the entire food chains of ecosystems will be broken, as these carnivorous dinosaurs would require large amounts of such species in order to sustain them. • This would result in large populations of the small animals to be completely wiped out in ecosystems, or even extinct. • If there would not be enough food to sustain the large dinosaurs with even larger appetites, they would not evolve into bigger creatures, and would end up living as the smaller descendants of dinosaurs they are today, such as the lizards and birds. • Because the closest living ancestors to the dinosaurs are birds, as observed by their similar characteristics, in both physical appearance, bone structures, and natural behaviors, even if the birds were to evolve towards the same route to become dinosaurs, they would no longer be the same dinosaurs as seen back then.

…continued • Birds nowadays utilize their current traits of wings for hunting and spotting prey from afar. • These wings allow birds to be more inconspicuous to the prey, and reach higher areas, which therefore improves their chances of acquiring foods. • Their wings also provides secure distance from predators that may not be able to fly. • Thus even if birds were to evolve, they would remain to be winged, as it is a very valuable characteristic. The most the birds will evolve to be similar to are Pterodactyl-like species. • For birds, like chickens, which are unable to fly, although many similar protein and collagen sequences are to be found similar within the genetic build of the chickens when compared to the fossils of dinosaurs, most chickens have experienced ‘artificial selection’. • This causes such species of birds to rely more on humans and artificial habitats and resources for survival, rather than on their own abilities and surroundings.

The Overall Conclusion • The reappearance of dinosaurs depends heavily on the environment that would exist if the temperature had increased by 2 degrees Celsius. At the moment, humans also present a great barrier to any possibility of dinosaurs: for instance, pollution would be an impediment to dinosaurs, which relied heavily on their sense of smell. (We are also known for being destructive.) • Despite the similarities between dinosaurs and their modern descendants, we probably won’t see the exact structures of dinosaur species coming back. • We believe it is unlikely that dinosaurs of the past will return, due to the improbability of necessary conditions occurring.

WILL DINOSAURS RETURN?