Charles Darwin's Theory Of Natural Selection

Evolution is a theory that gives origin to Earth’s living things. The theory of evolution is considered as one of the fundamental keystones of biology. Even though it is only considered a theory, in biology theories are supported by much experimental evidence and express ideas that are certain. Evolution accounts for life’s unity and diversity. The hypothesis of evolution was first introduced by Jean Baptiste Lamarck in 1809. Lamarck proposed how life changes over time. His principles included the inheritance of acquired characteristics and the innate tendency to increase perfections. His principles were incorrect but definitely started the big discussion of evolution. Between 1831 and 1836, Charles Darwin took a voyage around the world including

the Galapagos Islands where Darwin’s research and evidence to his theory of evolution was conducted. In 1859, Darwin published On the Origin of Species, which included his theory of evolution and earlier publications of descent with modification and his hypothesis of natural selection.

Darwin’s theory of evolution gave evidence of descent with modification from common ancestors and natural selection, which is the mechanism of descent with modification. With Darwin’s theory of evolution, evolution is redefined as descent modification with the change in the frequency of alleles over time. Natural selection is defined as individuals with certain traits that tend to survive and reproduce at higher rates because of the traits. Adaptations arise through the process of natural selection. Adaptations are inherited characteristics of the organism that help to enhance their survival and reproduction. With the help of Darwin and the understanding of how evolution and the different processes of evolution work, we are able to give correlations in the relationship between dinosaurs and birds and possibly come to the conclusion if today’s birds are related to extinct

dinosaurs.
About 250 to 210 million years ago during the Triassic period, all of the continents were joined together and called Pangaea. The supercontinent, Pangaea, had a very hot and dry climate since much of the land was far away from the oceans. Dinosaurs appeared late in the Triassic period but its ancestor, the archosaurs, was dominate earlier this period. The dinosaur closest related to the ancestor was the Marasuchus. Even though theropods were known in this period, the diversity of dinosaurs began to spread rapidly. Dinosaurs, like the Euraptor, Coelophysis and Herrerasaurus were all carnivores and rare during this time period. The rise of dinosaur species became noticeable when the early dinosaurs took advantage of the vacant niches after other extinctions had occurred. Carnivorous saurischian dinosaurs like the Coelophysis and the larger; Herrerasaurus occupied the niche previously owned by the ancestor carnivorous archosaurs. The environmental changes did not have much effect on the dinosaurs as it did to the previous reptiles. Other saurischians, like the Plateosaurus, showed evolutionary changes like larger sizes and adapting to being an herbivore. (Evolution of Dinosaurs)
About 210 to 150 million years ago during the Jurassic period, Pangaea was beginning to experience continental drift and dinosaurs dominated the land.

With the lands drifting apart, small waterways were being created and dinosaurs were able to spread out amongst the continents. Dinosaurs’ diversity began to rapidly spread with the extinction of mammal-like reptiles. With the Jurassic period’s climate, larger dinosaurs were able to evolve. The prosauropods, as mentioned in the Triassic period continued to give evidence of evolution, with the steady increase in size. For example, the 10 m long sauropod Vulcanodon shows numerous changes to its skeletal structure in order to accommodate the increase of weight. The Vulcanodon was the pioneer for great evolution among sauropods during the Jurassic period. Another sauropod named Brachiosaurus, evolved to have a very long neck and elongated forelimbs in order to reach high vegetation, while the other sauropods adapted to lower vegetation. Large ornithischian herbivores, like the Scelidosaurus, evolved a turtle-like beak for vegetation of lower plants and primitive iguanodonts, like the Camprosaurus, also showed adaptations for low grazing. The largest carnivore of the Jurassic period was the double-crested Dilophosaurus evolved from the Coelophysis. (Evolution of

Dinosaurs)
The Cretaceous period, about 150 to 65 million years ago, was the period of the dinosaurs’ greatest diversity. The continents were similar to the present day continents. The climate was warm and the water ways ran deep. Since the land mass was separated, dinosaur groups were isolate and able to evolve separately because there was no breeding and genetic variation. The larger saurischian sauropods from the Jurassic period were rare and smaller ornithischian dinosaurs, who exhibited greater diversity, replaced them. Since the sauropods had difficulty adapting a diet to the plants that had evolved in the Cretaceous period and environmental stresses on the large animals, they were replaced by the ornithopods. The largest ornithopods named Iguanodon, evolved a wide variety in its diet and are closely related to larger herbivores like the Tenontosaurus. The nodosaurs developed a horny beak like the iguanodonts and replaced the stegosaurs from the Jurassic period. The ostrich-like ornithomimus and 3 m long theropods Deinonychus were cretaceous carnivores. Deinonychus evolved to fit its carnivorous life style by obtaining a large retractable claw on the second toe. Researchers have found Deinonychus teeth and bones near the bones of the larger Tenontosaurus, which leads them to believe they preyed on the ornithopods. Other evolutions of the carnivores include very strong forelimbs in the largest carnivore, Tyrannosaurus and the Carnotaurus’ short snout and two horns over its eyes. Also introduced into the dinosaur diversity during the Cretaceous period are the duck-billed dinosaurs. They filled the niche similar to the closely related iguanodonts. Lambeosaurs’ skulls developed many different ornamental crests. Another group, including the Parasaurolophus, evolved hollow crest in which researchers believe they used them to conduct sounds for signaling. The dinosaurs became extinct at the end of the Cretaceous period, but many fossils were left as evidence for the presence and evolution of the species. (Evolution of Dinosaurs)