Grouping of organisms according to the similar anatomy helps to understand their evolution and how those organisms have being developed over millions of years. Similarly, structures of organisms have developed over years to function better to survive on the earth. Even though some organisms are unicellular, while some are multicelliular, both types of organisms have got particular structure to function that helps to fulfill their needs. Thus, structure and function of the organisms, including humans, portray the incredible creations of the nature (Campbell et al. 2008).
The phylogenic tree reveals the evolutionary history of animals simply. In this phylogenic tree, humans and other animals that are familiar to us are included in phylum chordates. Possessing a dorsal notochord or hollow nerve cord is the significant development of chordates. The nerve cord is a flexible structure and allows the body of the organism to extend. There are other important developments, too, such as metameric arrangement of organs and body regions, perforated pharynx, post-anal tail, large coelom, and ventral heart. These are more advance developments of phylum Chordates compare to the other phyla such as annelids, moluccas and so on. Chordates divide into three main clades such as cephalochordates, urochordates and vertebrates. The subphylum vertebrate shows even more advance development of structure of organisms. It is important to know more about vertebrata since human and other animals such as dogs, cows, birds, and the other most familiar animals are fallen into the subphylum vertebrates (Campbell et al. 2008).
The major development of vertebrata is the replacement of notochord by the segmented vertebrae and possession of cranium, which protects the brain. The subphylum vertebra is divided in to seven classes: class agnatha, class chondrichthyes, class osteichthyes, class amphibia, class reptilia, class mammalia, and class aves . Even though every class has some common attributes such as segmented vertebrae, specialization of the structure occurs in each class according to their function and the surviving environment. As such, organisms in class reptilian have got distinctive features that of aves, chondrichthyes, mamalia, and so on (Campbell et al. 2008).
The class reptilia is mostly terrestrial organisms. Class reptilian is included snakes, lizards known as Gecko, crocodiles, and so on. The amniotic egg is the most significant feature of reptilian. The amniotic egg is an essential stage of the life cycle of reptilian that helps them to complete their life cycle without water. The body structure of reptilians is specialized to survive in terrestrial environment. Consequently, many reptilians have got four limbs for locomotion. Locomotion is essential for reptilians to live in terrestrial environments (Campbell et al. 2008). Furthermore, the organisms that are categorized into the class reptilian, have different distinguish figures such as Gecko has sticky...