User:KnowledgeRequire/Vertebrate Evolution
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This article is about the Evolutionary history of Vertebrates. For general information on Vertebrates, see Vertebrate.
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Vertebrate(formally known as Vertebrata) is a subphylum taxon classified under the phylum of Chordates. Organisms of this taxon are defined by the existence of a spinal cord and backbones, which are constructed with bone and cartilage. All vertebrates are also distinguished from other organisms by developing a cranium, used to protect the central nervous system. Tetrapod vertebrate develop two sets of appendages in forms of: legs, arms, wings, flippers, and fins; fish species are constructed with varied number of fins, including the tail. Vertebrates do not develop external skeletons, like arthropods, but they have evolved anatomic structures upon their bodies. Reptiles and fishes are characterized by the existences of scales. Mammals develop hairs, while birds adapted feathers upon the majority of their body, with scales covering their feets. These anatomic structures all are constructed out of proteins called keratin.
Currently more than 40,000 species of vertebrates exist and are organized into the modern classes of: birds, amphibians, reptiles, mammals, and four classes of fish.
This article will mainly cover the evolution process of the major classes of vertebrates, and a few major orders.
The first vertebrates appeared about 500-450 million years ago, during the duration of the Ordovician Period.[1] The first member of this diverse group was represented by a species of jawless fish. This jawless fish, being the most basal species of this group, can be considered the ancestor of all vertebrates. Other fish classes emerged in the Silurian and Devonian period. During the late Devonian period, they underwent a transition to terrestrial life, evolving into amphibians. Amphibians radiated and dominated the terrestrial niche during the Carboniferous period, and then giving rise to reptiles. Reptiles increased in diversity in the Permian and the Mesozoic Era, which is often refered to as the Age of Reptiles. Here they evolved into mammals in the Late Triassic and birds in the Jurassic.