Animal classification systems are used extensively in taxonomy, the study of classification systems in nature. Each classification system differs on several factors, some of which are not well understood. Some classification systems have been proposed based on cladistics, others on functional elements like cladograms (focusing on similarities in derived patterns of characters across domains), whereas others rely on a combination of these and other techniques. Cladisticians and classpaths (morphologists) classify animals based on observed characteristics or characters, whereas classifiers use characters to predict relationships among taxa. We review classification strategies in detail in this article.
In classification, it is important to recognize the relationship among living organisms and their attributes. For example, humans, like all other organisms, belong to the animal kingdom; similarly, all plant and animal kingdoms belong to the kingdom Protista. Therefore, it is a mistake to apply the classifications based on similarities in fossils alone. According to Martinsson and coworkers ( 1976 ), humans and all other species of primates are a part of a genus H.H. and are therefore members of a clade, the H-group, of the larger genus H. priscus. On the other hand, all known large primate species are part of the genus E.H. and are therefore members of a clade called the Eutherians.
Phylogenetics is one of the methods used in animal classification. Phylogenetics studies variation in size and shape between closely related animals, and infer them to specific family members. Based on fossil evidence, Phylogenetics determines that whales, lizards, chiropotes, and all other known large and extinct animals belong to a branch of Prototheria, the most basal fossil ancestor of all living animals. Several other classifications based on fossil evidence are Evolutionary Biology, The Tree of Life, and Systematics. The cladogenesis method is used in molecular biology to study the relationships among living things based on their genetic material.
One major problem with Phylogenetics is that it fails to distinguish among different animal families and separates the taxonomy of different animal families into two main categories. These categories, according to Phylogenetics, are into two main subsets. The first consists of taxa that are derived exclusively from modern human ancestors and are thus to be regarded as universal species. These taxa include all the known mammals and fishes, including all dinosaurs and their subspecies. The second category consists of other taxa that derive from a parallel ancestry shared by modern humans and all other modern animals but are not derived from a modern human ancestor.
To solve the problems of Phylogenetics and Philology, comparative anatomy and dental anatomy of dinosaurs and modern-day mammals have been studied using comparative study and morphological descriptions. Many studies on the relationships among dinosaurs and mammals as well as other animals have been supported by morphological and fossil data. In addition, a comparative study has provided enough evidence for the existence of at least one previously undiscovered Kingdom of animals among the dinosaurs.
Among these kingdoms of animals, two major subsets have been recognized, the Saurian and Ornithischia. The Saurian Kingdom of animals includes all those animals which do not belong to the Kingdom Animalia. It is composed of four subphases sections: The Saurian Cyst Classifications, The Saurian Lagoon Classifications, The Saurian Anovolsk Classifications, and The Saurian Ceratonychia Classifications. The latter contains representatives of all the classes of dinosaurs. The Ceratonychia includes the egg-producing organs and also the embryos and growing bodies of animals.
The other major Kingdom of the animal kingdom is the Ornithischia. The major part of Ornithischia contains the representatives of all the classes of vertebrates. Most of the classification of vertebrates is based upon the information regarding the comparative study of these animals. Accordingly, to classify animals according to these data, several classifications have been developed.
One of the best-known classification systems is that based on the taxonomy according to Phylogenetics. According to this system, dinosaurs are classified according to the same kingdoms and sub-kingdom as modern birds and dinosaurs. Within Phylogenetics, dinosaurs are classified into three main categories, the iguanodon, the megalosaurus, and the Stegosaurus. So far, the exact classification of dinosaurs remains unknown.