Dinosaur 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. Some birds survived the extinction event that occurred 66 million years ago, and their descendants continue the dinosaur lineage to the present day. 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
Ornithopod Ornithopods /ɔrˈnɪθɵpɒd/ or members of the clade Ornithopoda /ɔrnɨˈθɒpədə/ are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American landscape. Their major evolutionary advantage was the progressive development of a chewing apparatus that became the most sophisticated ever developed by a non-avian dinosaur, rivaling that of modern mammals like the domestic cow. They reached their apex in the duck-bills, before they were wiped out by the Cretaceous–Paleogene extinction event along with all other non-avian dinosaurs. Members are known from all seven continents, though they are generally rare in the Southern Hemisphere. Description The early ornithopods were only about 1 metre (3 feet) long, but probably very fast. Sizes of the largest ornithopods Classification Taxonomy Phylogeny
Primates A primate ( With the exception of humans, which inhabit every continent,[a] most primates live in tropical or subtropical regions of the Americas, Africa and Asia. They range in size from Madame Berthe's mouse lemur, which weighs only 30 g (1 oz), to the eastern lowland gorilla, weighing over 200 kg (440 lb). Based on fossil evidence, the earliest known true primates, represented by the genus Teilhardina, date to 55.8 million years old. An early close primate relative known from abundant remains is the Late Paleocene Plesiadapis, circa 55–58 million years old. Molecular clock studies suggest that the primate branch may be even older, originating in the mid-Cretaceous period around 85 mya. Considered generalist mammals, primates exhibit a wide range of characteristics. Some primates (including some great apes and baboons) are primarily terrestrial rather than arboreal, but all species possess adaptations for climbing trees. Historical and modern terminology
Bird Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Extant birds have wings; the most recent species without wings was the moa, which is generally considered to have become extinct in the 16th century. Wings are evolved forelimbs, and most bird species can fly. Flightless birds include ratites, penguins, and diverse endemic island species. Some species of birds, particularly penguins and members of the Anatidae family, are adapted to swim. Many species are economically important, mostly as game or poultry. Evolution and classification Definition Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria. Gauthier identified four conflicting ways of defining the term "Aves", which is a problem because the same biological name is being used four different ways. Dinosaurs and the origin of birds
Crocodylomorpha Crocodylomorpha is an important group of archosaurs that includes the crocodilians and their extinct relatives. During Mesozoic and early Cenozoic times, Crocodylomorpha was far more diverse than it is now. Triassic forms were small, lightly built, active terrestrial animals. These were supplanted during the early Jurassic by various aquatic and marine forms. The Later Jurassic, Cretaceous, and Cenozoic saw a wide diversity of terrestrial and semi-aquatic lineages. "Modern" crocodilians do not appear until the Late Cretaceous. Evolutionary history When their extinct species and stem group are examined, the crocodylian lineage (clade Crurotarsi) proves to have been a very diverse and adaptive group of reptiles. During the Jurassic and the Cretaceous, marine forms in the family Metriorhynchidae, such as Metriorhynchus, evolved forelimbs that were paddle-like and had a tail similar to modern fish. Phylogenetic definition Taxonomy and phylogeny Phylogeny References
Hominidae The Hominidae (/hɒˈmɪnɨdiː/; also known as great apes[notes 1]) form a taxonomic family of primates, including four extant genera: The term "hominid" is also used in the more restricted sense as hominins or "humans and relatives of humans closer than chimpanzees". In this usage, all hominid species other than Homo sapiens are extinct. A number of known extinct genera are grouped with humans in the Homininae subfamily, others with orangutans in the Ponginae subfamily. The most recent common ancestor of the Hominidae lived roughly 14 million years ago, when the ancestors of the orangutans speciated from the ancestors of the other three genera. The ancestors of the Hominidae family had already speciated from those of the Hylobatidae family, perhaps 15 million to 20 million years ago. History Taxonomic history The classification of the great apes has been revised several times in the last few decades. Especially close human relatives form a subfamily, the Homininae.
Cretaceous The Cretaceous (/krɨˈteɪʃəs/, krə-TAY-shəs), derived from the Latin "creta" (chalk), usually abbreviated K for its German translation Kreide (chalk), is a geologic period and system from circa 145 ± 4 to 66 million years (Ma) ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the Cenozoic era. It is the last period of the Mesozoic Era, and, spanning 79 million years, the longest period of the Phanerozoic Eon. Geology Key events in the Cretaceous An approximate timescale of key Cretaceous events. Research history Stratigraphic subdivisions As with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact ages of the system's base is uncertain by a few million years. Rock formations The high eustatic sea level and warm climate of the Cretaceous meant a large area of the continents was covered by warm shallow seas. Paleogeography Climate Life
Ceratopsia Triceratops are by far the best-known ceratopsians to the general public. It is traditional for ceratopsian genus names to end in "-ceratops", although this is not always the case. One of the first named genera was Ceratops itself, which lent its name to the group, although it is considered a nomen dubium today as its fossil remains have no distinguishing characteristics that are not also found in other ceratopsians. Anatomy Centrosaurus, with large nasal horn, exaggerated epoccipitals, and bony processes over the front of the frill. Museum of Victoria. Ceratopsians are easily recognized by features of the skull. History of study The first ceratopsian remains known to science were discovered by Fielding Bradford Meek during the U.S. Classification Taxonomy Triceratops, one of the largest ceratopsians (a chasmosaurinae ceratopsid). Following Marsh, Ceratopsia has usually been classified as a suborder within the order Ornithischia. Phylogeny