A basic knowledge of dinosaur anatomy is required for understanding why dinosaurs are classified as dinosaurs (as opposed to reptiles, mammals, or birds) and why they are then subdivided into different groups. The anatomical distinctions that facilitate the classification of dinosaurs are most readily apparent as features preserved in their hard parts (bones and teeth). Learning about dinosaur anatomy is not difficult if the location names (e.g., anterior, posterior, dorsal, ventral), universally used in describing the anatomy of other animals, are applied to dinosaurs. Furthermore, anatomical features, primarily represented by bones, are homologous to those found in many vertebrates, so learning about these features clarifies and reinforces knowledge of general vertebrate anatomy. Bones of the axial, appendicular, and cranial skeleton of dinosaurs, as well as rare examples of soft anatomy (skin, feathers, or organs), provide paleontologists with evidence for reconstructing dinosaurs as living animals and assist in the classification of dinosaurs into different groups.
The two main classification systems used for dinosaurs and other organisms, Linnaean and cladistics, are similar in their use of categories and some taxonomic designations, but differ in key ways. Advocates of the Linnaean classification attempt to classify dinosaurs on the basis of how closely they resemble one another and place them into hierarchal groups. Cladistics can resemble a hierarchy but also emphasizes identification of inheritable traits (synapomorphies) and defines dinosaur groups on the basis of how many of these traits are shared. This method thus includes all descendants of an ancestor in a group as a clade, which is a phylogenetically-based grouping. Knowing how some clades of dinosaurs are classified, such as the Theropoda, Sauropodomorpha,
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