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Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic period, 231.4 million years ago, and were the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic (about 201 million years ago) until the end of the Cretaceous (66 million years ago), when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups at the close of the Mesozoic Era. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic Period and, consequently, they are considered a subgroup of dinosaurs by many paleontologists.[1] Some birds survived the extinction event that occurred 66 million years ago, and their descendants continue the dinosaur lineage to the present day.[2] Etymology Definition The common House Sparrow (Passer domesticus) is often used to represent modern birds in definitions of the group Dinosauria General description Distinguishing anatomical features

Related:  Tree of Life - Phylogenetic systematics

Tree of life - Wikipedia Cancel Edit Delete Preview revert Text of the note (may include Wiki markup) Could not save your note (edit conflict or other problem). Please copy the text in the edit box below and insert it manually by editing this page. Ceratosauria Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is no agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived anatomically than the more diverse Tetanurae. According to the latest and most accepted theory, Ceratosauria includes the Late Jurassic to Late Cretaceous theropods Ceratosaurus, Elaphrosaurus, and Abelisaurus, found primarily (though not exclusively) in the Southern Hemisphere. Originally, Ceratosauria included the above dinosaurs plus the Late Triassic to Early Jurassic Coelophysoidea and Dilophosauridae, implying a much earlier divergence of ceratosaurs from other theropods. However, most recent studies have shown that coelophysoids and dilophosaurids do not form a natural group with other ceratosaurs, and are excluded from this group. Relationships[edit]

Laurasia Origin[edit] Although Laurasia is known as a Mesozoic phenomenon, today it is believed that the same continents that formed the later Laurasia also existed as a coherent supercontinent after the breakup of Rodinia around 1 billion years ago. To avoid confusion with the Mesozoic continent, this is referred to as Proto-Laurasia. It is believed that Laurasia did not break up again before it recombined with the southern continents to form the late Precambrian supercontinent of Pannotia, which remained until the early Cambrian. Laurasia was assembled, then broken up, due to the actions of plate tectonics, continental drift and seafloor spreading. Breakup and reformation[edit] International Code of Zoological Nomenclature How names are correctly established in the frame of binominal nomenclatureWhich name must be used in case of name conflictsHow scientific literature must cite names Zoological nomenclature is independent of other systems of nomenclature, for example botanical nomenclature. This implies that animals can have the same generic names as plants. In other words, whether a species itself is or is not a recognized entity is a subjective decision, but what name should be applied to it is not. The Code applies only to the latter, not to the former. A new animal name published without adherence to the Code may be deemed simply "unavailable" if it fails to meet certain criteria, or fall entirely out of the province of science (e.g., the "scientific name" for the Loch Ness Monster).

Abelisauridae Like most theropods, abelisaurids were carnivorous bipeds. They were characterized by stocky hindlimbs and extensive ornamentation of the skull bones, with grooves and pits. In many abelisaurids, like Carnotaurus, the forelimbs are vestigial, the skull is shorter and bony crests grows above the eyes. Most of the known abelisaurids would have been between 5 to 9 meters (17 to 30 ft) in length, from snout to tip of tail, with a new and as yet unnamed specimen from northwestern Turkana in Kenya, Africa reaching a possible length of 11–12 meters (36 to 39 feet).[2] Before becoming well known, fragmentary abelisaurid remains were occasionally misidentified as possible South American tyrannosaurids.[3] Description[edit] Reconstructed Abelisaurus skull, "Dinosaurs of Patagonia" exhibit.

Archosaur Archosaurs are a group of diapsid amniotes whose living representatives consist of birds and crocodilians. This group also includes all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most recent common ancestor of living birds and crocodilians. Taxon The idea of a "natural system" of classification goes back to the dawn of scientific nomenclature in the mid-18th century, as indicated by the title of Carolus Linnaeus' 1758 Systema Naturae. Systematists since that time have striven to determine the true classification of the diversity of life, which was at that time thought to reflect the Plan of Creation. Today it is common to define a "good taxon" as one that reflects evolutionary (phylogenetic) relationships.

Paleontology Paleontology or palaeontology (/ˌpeɪlɪɒnˈtɒlədʒi/, /ˌpeɪlɪənˈtɒlədʒi/ or /ˌpælɪɒnˈtɒlədʒi/, /ˌpælɪənˈtɒlədʒi/) is the scientific study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments (their paleoecology). Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term itself originates from Greek παλαιός, palaios, i.e. Gondwana The adjective Gondwanan is in common use in biogeography when referring to patterns of distribution of living organisms, typically when the organisms are restricted to two or more of the now-discontinuous regions that were once part of Gondwana, including the Antarctic flora. For example, the Proteaceae family of plants known only from southern South America, South Africa, Australia and New Zealand is considered to have a "Gondwanan distribution". This pattern is often considered to indicate an archaic, or relict, lineage. Formation[edit]

Reading trees: A quick review Reading trees: A quick review A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa (singular: taxon). The tips of the tree represent groups of descendent taxa (often species) and the nodes on the tree represent the common ancestors of those descendants. Spinosauridae Spinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look. Therapsida Therapsida is a group of synapsids, and includes mammals and their ancestors.[1][2] Many of the traits today seen as unique to mammals had their origin within early therapsids, including an erect posture. The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian.[3][4] Therapsids evolved from pelycosaurs (specifically sphenacodonts) 275 million years ago. They replaced the pelycosaurs as the dominant large land animals in the Middle Permian and were replaced, in turn, by the archosauromorphs in the Triassic, although one group of therapsids, the kannemeyeriiforms, remained diverse in the Late Triassic. The therapsids included the cynodonts, the group that gave rise to mammals in the Late Triassic around 225 million years ago.