An Introduction
Four young biologist detectives have been given the task of answering the question that has stumped scientists for eons. Will the dinosaurs ever make a comeback? Equipped with a strong will, trusty computers, and a bit of hair-pulling, Priscilla Choi, Daniel Gao, Justine Hansen, and Cathy Jiang will do their best to convince you, the site guest, that dinosaurs can indeed, return. This has been done in the view of a geneticist, paleontologist, and physiologist. Welcome to their findings.
Note: green words can be clicked on and they are usually teleportation pads to the vocabulary page. (Like this.)
Background Information
Mechanisms For Evolution
There are four basic mechanisms of evolution: genetic drift, natural selection, mutation, and migration. All four contribute greatly of the evolution and extinction of dinosaurs.
Genetic Drift
Genetic drift is the random reduction or elimination of a gene. Every generation, by chance some individuals may leave (die, migrate, etc.). If this random elimination of certain individuals causes a change in the genotypic ratio in a population, the more popular gene may prosper. After several generations, it is entirely possible for the other gene to completely die out-- because of the completely random genetic “drift.”
Ex. In a population of five green beetles and five brown beetles, four green beetles may be stepped upon by me (involuntarily). The population that remains to mate with each other now includes only one green beetle. The chance that there will be a substantial amount of green beetles in second generation is now very low. Over time, the gene for the green beetle may die out.
Genetic Drift
Genetic drift is the random reduction or elimination of a gene. Every generation, by chance some individuals may leave (die, migrate, etc.). If this random elimination of certain individuals causes a change in the genotypic ratio in a population, the more popular gene may prosper. After several generations, it is entirely possible for the other gene to completely die out-- because of the completely random genetic “drift.”
Ex. In a population of five green beetles and five brown beetles, four green beetles may be stepped upon by me (involuntarily). The population that remains to mate with each other now includes only one green beetle. The chance that there will be a substantial amount of green beetles in second generation is now very low. Over time, the gene for the green beetle may die out.
Dinosaur application: As the continents of Pangaea began separating (continental drift), streams flowed in between the continents and separated the dinosaurs. Thus, genes were separated as well. Through this separation, genes could have been lost (and gained!) and the ratio of certain genes would change.
Mutations
Mutations are a change in the DNA. They occur when a nucleotide base (A, T, C, or G) is wrongly paired up with another nucleotide base during reproduction. Mutations can cause new genes to surface in the gene pool of a population. Mutations are completely random. These mutations (which are not necessarily either good or bad) create a change in the organisms DNA and may affect a protein and its result. Beneficial mutations may change the organism in such an extreme way that it makes it possible for an entirely new species to branch off of the original organism (without the mutation). One of the largest aspects of evolution is the mutations that occur DNA.
Example: Cancer, sickle cell disease, and other diseases can be acquired through DNA mutation.
Mutations are a change in the DNA. They occur when a nucleotide base (A, T, C, or G) is wrongly paired up with another nucleotide base during reproduction. Mutations can cause new genes to surface in the gene pool of a population. Mutations are completely random. These mutations (which are not necessarily either good or bad) create a change in the organisms DNA and may affect a protein and its result. Beneficial mutations may change the organism in such an extreme way that it makes it possible for an entirely new species to branch off of the original organism (without the mutation). One of the largest aspects of evolution is the mutations that occur DNA.
Example: Cancer, sickle cell disease, and other diseases can be acquired through DNA mutation.
Dinosaur application: Mutation was one of the many reasons for the diversity of dinosaurs, and the allowance of dinosaurs to spread and create their own dominant species. Examples of “good” mutations lie in the evolution of dinosaurs and the benefits of different structural function (such as horns, long necks, big feet, small arms, etc.).
Natural Selection
Natural selection occurs as certain genes increase or decrease in frequency based on their advantage or disadvantage to a certain environment. Organisms with a gene that is advantageous in their environment will have a better chance of surviving than other organisms without this “beneficial” gene. Since the “beneficial” gene can survive easier, it can also reproduce with greater success. This results in a second generation full of the “beneficial” gene. Over time, the population’s genotypic ratio will be heavily dominated on the gene that helps organisms to survive.
Example: Some green beetles and some brown beetles live together as a population in the dry grasslands. The colour of the brown beetles will camouflage with the brown background, whereas the striking colour of the green beetles will stand out like a sore thumb. Thus, the predators (ie. birds), will see and eat the green beetles much more than they eat the brown beetles. Over time, the population will evolve to be brown, where the brown colour is the “beneficial” gene.
Natural selection occurs as certain genes increase or decrease in frequency based on their advantage or disadvantage to a certain environment. Organisms with a gene that is advantageous in their environment will have a better chance of surviving than other organisms without this “beneficial” gene. Since the “beneficial” gene can survive easier, it can also reproduce with greater success. This results in a second generation full of the “beneficial” gene. Over time, the population’s genotypic ratio will be heavily dominated on the gene that helps organisms to survive.
Example: Some green beetles and some brown beetles live together as a population in the dry grasslands. The colour of the brown beetles will camouflage with the brown background, whereas the striking colour of the green beetles will stand out like a sore thumb. Thus, the predators (ie. birds), will see and eat the green beetles much more than they eat the brown beetles. Over time, the population will evolve to be brown, where the brown colour is the “beneficial” gene.
Dinosaur application: Beneficial dinosaur genes prosper and others don’t. Eventually, the population will evolve to hold only one “beneficial” genotype. Dinosaurs without a “beneficial” gene will die out, & new organisms will prosper.
Migration
Migration occurs when a different phenotype joins the population of organisms.
Example: A green beetle joins the population of several brown beetles. The ratio (brown: green) has changed. If more green beetles continue migrating into the originally brown population, the green beetles may make a large effect on the phenotype and genotype of later generations. The “green gene”, which used to be foreign to the population, is now included in the offspring
Migration occurs when a different phenotype joins the population of organisms.
Example: A green beetle joins the population of several brown beetles. The ratio (brown: green) has changed. If more green beetles continue migrating into the originally brown population, the green beetles may make a large effect on the phenotype and genotype of later generations. The “green gene”, which used to be foreign to the population, is now included in the offspring
Dinosaur application: Migration allows the diversity of dinosaurs to expand due to a larger variety of phenotypes.
Theories for extinction (More Later...)
Facts: 66 million years ago, a catastrophic event, that occurred under a geologically short period of time, wiped out the dinos that had been around for 150 millions years along with 70% of life on earth.
Theories:
1) An asteroid impact created a cloud of dust that blocked the sunlight for an extended period of time, making life impossible for many animals. This is the most favoured theory by far and explains many things. For example, many scientists have suggested that the reason crocodiles survived the mass extinction is because of their ability to live in water.
2) Sudden temperature drop and climate change. The world could have gone into an ice age, killing unsuited dinosaurs. The death of plants as temperature dropped would have taken away the food source of herbivores and as a result that of the carnivores. There was an observed decline of plankton in that time period so that could have led to the starvation of water dinosaurs.
3) Mass volcano eruptions could have had similar effects with the asteroid impact, creating clouds of dust that block out sunlight
4) They could have been wiped out by mass diseases.
*The theories of extinction will be further discussed in the Paleontologist section.
Theories:
1) An asteroid impact created a cloud of dust that blocked the sunlight for an extended period of time, making life impossible for many animals. This is the most favoured theory by far and explains many things. For example, many scientists have suggested that the reason crocodiles survived the mass extinction is because of their ability to live in water.
2) Sudden temperature drop and climate change. The world could have gone into an ice age, killing unsuited dinosaurs. The death of plants as temperature dropped would have taken away the food source of herbivores and as a result that of the carnivores. There was an observed decline of plankton in that time period so that could have led to the starvation of water dinosaurs.
3) Mass volcano eruptions could have had similar effects with the asteroid impact, creating clouds of dust that block out sunlight
4) They could have been wiped out by mass diseases.
*The theories of extinction will be further discussed in the Paleontologist section.
Although the mass extinction after the Cretaceous wasn't as massive as the Permian extinction, it still wiped out the large animals, the flying reptiles (pterosaurs), and the last of the mosasaurs and plesiosaurs. Rudistid, inoceramid clams, ammonites, and belemnites, were also among the many organisms that went extinct. Terrestrial plants and microscopic marine plankton also suffered severe losses. Many organisms that "survived" the catastrophic event died anyways due to a lack of a sustainable environment. Many insects also went extinct, especially those who fed mostly on a specific type of plant. However, with all these terrors in mind, don't forget that many organisms survived and gave rise to the new species we see today.
