In discussing the phylogeny of animals, plants, and fungi, we emphasized the maj
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In discussing the phylogeny of animals, plants, and fungi, we emphasized the major adaptations or “watershed events” that led to completely new types of organisms, such as the transition from fish to amphibian or gymnosperm to flowering plants. Choose at least three of these major adaptations and describe how these adaptations allowed specific organisms to have a selective advantage over their ancestors and thus proliferate and give rise to new tax’s. Describe the most probable ancestral type, the transitional type, and the descendent type of organism for each major adaptation. Describe how that adaptation may have changed from one function to another. In discussing the phylogeny of animals, plants, and fungi, we emphasized the major adaptations or “watershed events” that led to completely new types of organisms, such as the transition from fish to amphibian or gymnosperm to flowering plants. Choose at least three of these major adaptations and describe how these adaptations allowed specific organisms to have a selective advantage over their ancestors and thus proliferate and give rise to new tax’s. Describe the most probable ancestral type, the transitional type, and the descendent type of organism for each major adaptation. Describe how that adaptation may have changed from one function to another.Explanation / Answer
Evolution of Amphibians
Current amphibians, together with reptiles, birds and mammals are found within the superclass Tetrapoda (“four limbs”), the vertebrate group that abandoned the sea to conquer the land. These first tetrapods were amphibians and they evolved around 395 million years ago during the Devonian period from lobe-finned fish named sarcopterygians (class Sarcopterygii, “flesh fins”) within which we find the coelacanth and the current lungfish.
This group of fish is characterized by its fins which, instead of being formed by rays like in most bony fish, they have a bony base that allowed the subsequent evolution of the limbs of the first amphibians. Within the sarcopterygians, the nearest relatives of the tetrapods are the osteolepiformes (order Osteolepiformes) a group of tetrapodomorph fish that got extinct about 299 million years ago. The adapations which were slowly acquired for the transition into the amphibians were:
1. Evolution of Lungs
2. Development of choanaes/ infundibulum
3. Unusual appearance of the quiridium-like limb
Evolution of mammals
Hair was first evolved in early mammals to help regulate temperatures. The earliest mammals grew these sensory cones between the scales of the evolving reptiles, which, when brushed on objects, gave a stimulus to the brain. Certain remnant scales still exist on rats' tails, armadillo shells and the backs of pangolins. Early in the evolution of the therapsids arose a group called the cynodonts. These early mammal-like reptiles changed their teeth from being designed for catching and holding prey and then swallowing whole, to adding specialized teeth, including molars, designed for better mastication of food allowing for quicker digestion. In reptiles, all the teeth are alike, being replaced alternately along the jaw in waves from the back of the jaw to the front. Larger, but similar teeth replace the earlier teeth. As the cynodonts progressed toward today's mammals, this process was replaced by the characteristic pattern of one set of deciduous teeth followed by one set of permanent teeth.
About 120 million years ago, the mammalian line ceased laying eggs and began bearing live young. These forms of mammals were the first marsupials, who bore their young at a very early stage in their development and transferred them to a pouch where modified sweat glands secreted milk. It is generally accepted that the first marsupials arose in North America and spread to South America, then to Antarctica and Australia some time before the breakup of Pangaea near the end of the Cretaceous period, some 70 million years ago. Others argue that a southern continental origin is more probable.
By, the end of the Cretaceous (65 million years ago), early Marsupials (and the limited number of Monotremes) were the sole inhabitants of the southern land mass, Gondwana, and the Marsupial lines radiated out to fill out every niche available.
Evolution of flowering plants
The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago (mya), and the first flowering plants are known from 160 million years ago. They diversified extensively during the Lower Cretaceous, became widespread by 120 million years ago, and replaced conifers as the dominant trees from 100 to 60 million years ago.
Flowers, the reproductive organ of flowering plants, are the most remarkable feature distinguishing them from the other seed plants. Flowers provided angiosperms with the means to have a more species-specific breeding system, and hence a way to evolve more readily into different species without the risk of crossing back with related species. Faster speciation enabled the Angiosperms to adapt to a wider range of ecological niches. This has allowed flowering plants to largely dominate terrestrial ecosystems.
Stamens are much lighter than the corresponding organs of gymnosperms and have contributed to the diversification of angiosperms through time with adaptations to specialized pollination syndromes, such as particular pollinators. Stamens have also become modified through time to prevent self-fertilization, which has permitted further diversification, allowing angiosperms eventually to fill more niches.
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