FIGURE 1.3 Cladogram of the major dinosaur clades covered in this text, using Saurischia and Ornithischia hip structures as a basis for dinosaur classification.
Although Linnaean and phylogenetic classification methods differ from one another, a comparison of categories used in each dinosaur classification shows that they use many of the same names. Unless antecedents such as "clade" or "Order" are used, confusion may result from not knowing which scheme a paleontologist is using. Consequently, many dinosaur paleontologists will merely abbreviate references to certain groups of dinosaurs through general categorical names, such as "theropods" (Chapter 9), "sauropods" and "prosauropods" (Chapter 10), or "ornithopods" (Chapter 11), although nowadays these designations implicitly refer to clades. Cladistics is used in this book because dinosaur paleontologists mostly use this method, and it is based on evolutionary relatedness. However, an awareness of the Linnaean system is helpful for understanding the extensive literature on dinosaurs published prior to the 1980s, and some even later.
One aspect of classifying dinosaurs, unchanged since Linnaean times is the tradition of naming species. The species name of a dinosaur or any other organism is based on the biological species concept, where a species is a population of organisms that can interbreed and produce offspring that can also reproduce with one another (Chapter 6). The species name was an elegant solution devised by Linné for problems associated with the common practice of applying numerous names to the same organism. The species name uses a binomial nomenclature, meaning that two italicized names are used together, a capitalized genus name followed by a lowercase trivial name, to name a species (i.e., Tyrannosaurus rex for a specific dinosaur, Homo sapiens for modern humans). The trivial name is "trivial" in the sense that it cannot be used by itself to identify an organism and must always be used in combination with and preceded by a genus name. However, the genus name can be used alone and represents a broader category that may include several species.
This principle is similar to that used by some Asian societies, who place the family name first and the surname second. For example, in Korea, the names Moon Jai-Woon and Moon Hyun-Soo both have the Moon family name (a general category) followed by their surnames, which identify specific individuals when used in combination. Species and other categories in the Linnaean classification originated with Latin and Greek roots for the sake of universal standards, which prompted such well-known dinosaur genus names such as Stegosaurus, Triceratops, Allosaurus, and Tyrannosaurus. Since Linné's time, many languages have contributed roots for taxonomic categories, a practice that is especially evident in species names seen throughout this book. For example, French, Spanish, German, Swahili, Mandarin Chinese, and Japanese, among others, have contributed to dinosaur species names.
Using cladistics as a framework, the names of major dinosaur groups, such as ceratopsians (Chapter 13), ceratosaurs (Chapter 9), hadrosaurs (Chapter 11), and prosauropods (Chapter 10), will be repeated throughout this book. Likewise, association of these groups with certain well-studied or otherwise famous dinosaur genera or species will provide an outline of general anatomical characteristics shared within such groups (Table 1.1), which will suffice for discussion of what information can be discerned from dinosaurs. Information about synapomorphies that define each clade will be given in greater detail in later chapters (Chapters 9 to 13).
LE 1.1 Summary of different major clade groups used to classify dinosaurs, general descriptions of anatomical characteristics for each group, and genus examples. Detailed classifications, less represented groups, and interrelationships are presented in Chapters 5 and 11 to 15.
Saurischia ("lizard-hipped" dinosaurs)
Theropoda: Late Triassic to Late Cretaceous; feet and legs reflect bipedal habit; hands able to grasp; hollow limb bones; teeth indicate meat eating; 1-16 m long.
Ceratosaurus Coelophysis Dilophosaurus
Sauropodomorpha: Late Triassic to Late Cretaceous; feet and legs reflect bipedal habit in some forms, quadrupedal in most others; often characterized by small head in proportion to rest of body and long necks; teeth indicate plant eating; 2-38 m long.
Lufengosaurus Coloradisaurus Riojasaurus
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