Its hard to believe that the large elegant marine mammals we know today, were once land dwelling creatures. Whales have been forever evolving just like humans. What is evolution? Evolution is the process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth (Mueller, Aug. 2010). Every living organism has evolved at one point or another.
However, it wasn’t until the late Devonian Period, 350 million years before present time, that the first vertebrates began to invade the land. These early vertebrates came in the form of amphibious tetrapods, organisms that had evolved from lobe finned fish. Although by their appearance these amphibious tetrapods may appear vastly similar to their fish ancestors, when looking at skeletal morphology of these creatures, one can see several distinct and major differences. It is these changes that will allow amphibious tetrapods to thrive on land, and set a base from the future evolution of reptiles, dinosaurs, mammals, and eventually humans. Skull Morphology As lobe finned fish began to evolve features that were better suited for living on land, one can see many changes taking place in the morphology of their skulls.
Introduction: Before tetrapods existed, all vertebrates were confined to living in aquatic habitats. The only animals that lived on land were arthropods. Through natural adaptations, the fish developed into amphibians. This colossal stage of change made necessary the evolution of new ways of breathing, locomotion, and reproduction. Paleontologists needed to understand how this transition took place.
“…Modern cetaceans are highly specialized, with numerous adaptations that allow them t... ... middle of paper ... ...ls. J. G. M. Thewissen and his colleagues changed the way in which scientists thought about the early lifestyles of whales. The evolution of the ancient artiodactyls was discovered to be joined with the well-known group of cetaceans. The tertiary period was a time of terrestrial life forms. Every mammal walked the earth.
At some point of their life they had a dorsal hollow nerve cord, a notochord, pharyngeal pouches, and a tail that extends beyond the anus. The development of the jaw was useful with the teeth and muscles, by... ... middle of paper ... ...parates species according to their common structure. Fossils show how tetrapod legs evolved from fins and genes studies show how mutation and natural selection resulted into long limb bones from the fins (Hoff). In this case, they have uncovered how a species that lives on water transitioned to a terrestrial way of life. It took millions of years for evolution to generate certain animal adaptations.
Primitive character is the feature of a group of organisms that is inherited from a common ancestor. In order words, an organism must share the same primitive character to be included in the group. Derived or secondary characters are features that are not shared with all organisms in a larger group because they evolve after the primitive character. From analyzing the fossil evidence, experts have discovered that early tetrapod amphibians evolved from lobe-fin fish. Amphibians are cold-blooded vertebrates animals that live under water and on land.
The earliest Ichthyosaur fossil findings were in parts of Canada, China, Japan, and possibly Thailand. Countless fossils came from coatings of limestone produced out of the ocean-floor ooze that was predominantly superior at preserving very well facts of the creatures it digested (Perkins 2). Andrea Fildani and Michael Shultz, graduate students in the Department of Geological and Environmental Sciences, uncovered the bones of an Ichthyosaur near the southernmost tip of Chilean Patagonia. These rock layers were initially deposited at the floor of an ocean more than 100 million years ago. In their findings of the Chilean boulder, they were fortunate enough to find 17 vertebrae along with neural arches that encircle the spinal cord as well as some ribs.
It is said that fishes were amongst the first vertebrates. The earliest fish to appear in the fossil record were jawless, covered with bony plates, gills, scales, but no fins. According to Arreola, they later evolved by adapting to their environment and began to form jaws and paired fins. The jaws were useful with their muscles and teeth, which helped them eat a wider variety of food, and were even able to defend themselves by bi... ... middle of paper ... ...is a form of evidence that shows how life has changed throughout the years and how species today are connected way back to a common ancestor. Paleontologists look for features from one way of life to another.
Most reptiles are oviparous meaning they are egg layers, although there are some reptiles that are viviparous meaning they carry a fetus in there stomach. The crocodilian has 25 species, squamata has over 9,600 species, and the testudines has approximately 400 species. The crocodilian is an order of a large predatory semiaquatic reptiles who have been around for millions of years. Roughly around 83.5 million years ago is when the crocodilian first appeared, the crocodilian family consists of the alligators, caimans, and the gavial idea family. Crocodilians are a solid massive lizard like reptile, they have long flattened snouts, and compressed tails.