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Mammaliformes
Mammaliaformes ("mammalian forms") is a clade that contains the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts. It is defined as the clade originating from the most recent common ancestor of Morganucodonta and the crown group mammals; the latter is the clade originating with the most recent common ancestor of extant Monotremata, Marsupialia, and Placentalia. Besides Morganucodonta and the crown group mammals, Mammaliaformes includes Docodonta and '' Hadrocodium'' as well as the Triassic ''Tikitherium'', the earliest known member of the group. Mammaliaformes is a term of phylogenetic nomenclature. In contrast, the assignment of organisms to Mammalia has traditionally been founded on traits and, on this basis, Mammalia is slightly more inclusive than Mammaliaformes. In particular, trait-based taxonomy generally includes ''Adelobasileus'' and ''Sinoconodon'' in Mammalia, though they fall outside the Mammaliaformes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Docodonta
Docodonta is an Order (biology), order of extinct Mammaliaformes, mammaliaforms that lived during the Mesozoic, from the Middle Jurassic to Early Cretaceous. They are distinguished from other early Mammaliaformes, mammaliaforms by their relatively complex Molar (tooth), molar teeth, from which the order gets its name. Until recently, Docodonta were represented primarily by teeth and jaws found across former Laurasia, (modern-day North America, Europe, and Asia). However, recent discoveries in China include some exceptionally well preserved, almost complete body fossils. Description Skeletal traits Docodonts have a long and low mandible (lower jaw), formed primarily by the tooth-bearing dentary bone. The dentary connects to the cranium via a joint with the Squamosal bone, squamosal, a connection which is strengthened relative to earlier mammaliaforms. The other bones in the jaw, known as postdentary elements, are still connected to the dentary and lie within a groove (the postd ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tikitherium
''Tikitherium'' is an extinct genus of mammaliaforms from the Late Triassic. It is thought to be an insectivore and a close relative to Docodonta. ''Tikitherium'' refers to Tiki, the village located near the Tiki Formation where the specimen was found, and ''therium'' is Greek for “Beast”. The species was named ''copei'' in honor of Edward Drinker Cope for his pioneering discoveries towards understanding mammalian molars.Datta, P.M. 2005. Earliest Mammal with Transversely Expanded Upper Molar from the Late Triassic (Carnian) Tiki Formation, South Rewa Gondwana Basin, India. Journal of Vertebrate Paleontology. 25(1):200-207. History and discovery ''Tikitherium copei'' was first described by Datta in 2005. The first and only specimen is an upper left molar that was discovered in the lower part of the Tiki Formation, located in the South Rewa Gondwana Basin, India. Both the genus ''Tikitherium'' and the species ''copei'' were named by Datta in 2005. The currently only known ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. The corresponding series (stratigraphy), series of rock beds is known as the Upper Triassic. The Late Triassic is divided into the Carnian, Norian and Rhaetian Geologic time scale, Ages. Many of the first dinosaurs evolved during the Late Triassic, including ''Plateosaurus'', ''Coelophysis'', and ''Eoraptor''. The Triassic–Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth. Etymology The Triassic was named in 1834 by Friedrich August von Namoh, Friedrich von Alberti, after a succession of three distinct rock layers (Greek meaning 'triad') that are widespread in southern Germany: the lower Buntsandstein (colourful sandstone'')'', t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown Group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade, a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants. The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen. Contents of the crown gr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phylogenetic Nomenclature
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which can be a specimen or a taxon of lower rank, and a description in words. Phylogenetic nomenclature is currently regulated by the '' International Code of Phylogenetic Nomenclature'' (''PhyloCode''). Definitions Phylogenetic nomenclature ties names to clades, groups consisting of an ancestor and all its descendants. These groups can equivalently be called monophyletic. There are slightly different ways of specifying the ancestor, which are discussed below. Once the ancestor is specified, the meaning of the name is fixed: the ancestor and all organisms which are its descendants are included in the named taxon. Listing all these organisms (i.e. providing a full circumscription) requires the full phylogenetic tree to be known. In practice, ther ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic Period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic. The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Three categories of organisms can be distinguished in the Triassic record: survivors from the extinction event, new groups that flourished briefly, and other new groups that went on to dominate the Mesozoic Era. Reptiles, especially archosaurs, were the chief terrestrial vertebrates during this time. A specialized subgroup of archo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Placentalia
Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished from monotremes and marsupials in that the fetus (biology), fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young which are then nurtured for a period inside the mother's pouch (marsupial), pouch. Anatomical features Placental mammals are anatomically distinguished from other mammals by: * a sufficiently wide opening at the bottom of the pelvis to allow the birth of a large baby relative to the size of the mother. * the absence of epipubic bones extending forward from the pelvis, which are found in all other mammals. (Their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Marsupialia
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a pouch (marsupial), pouch. Marsupials include opossums, Tasmanian devils, kangaroos, koalas, wombats, Wallaby, wallabies, bandicoots, and the extinct thylacine. Marsupials represent the clade originating from the last common ancestor of extant metatherians, the group containing all mammals more closely related to marsupials than to Placentalia, placentals. They give birth to relatively undeveloped young that often reside in a pouch located on their mothers' abdomen for a certain amount of time. Close to 70% of the 334 extant taxon, extant species occur on the Australia (continent), Australian continent (the mainland, Tasmania, New Guinea and nearby islands). The remaining 30% are found in the Americas—primarily in South America, thirteen in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cynodont
The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety of lifestyles, including carnivory and herbivory. Mammals are cynodonts, as are their extinct ancestors and close relatives, having evolved from advanced probainognathian cynodonts during the Late Triassic. All other cynodont lines went extinct, with the last known non-mammalian cynodont group, the Tritylodontidae, having its youngest records in the Early Cretaceous. Description Early cynodonts have many of the skeletal characteristics of mammals. The teeth were fully differentiated and the braincase bulged at the back of the head. Outside of some crown-group mammals (notably the therians), all cynodonts probably laid eggs. The temporal fenestrae were much larger than those of their ancestors, and the widening of the zygomatic arch in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Probainognathia
Probainognathia is one of the two major subgroups of the clade Eucynodontia, the other being Cynognathia. The earliest forms were carnivorous and insectivorous, though some groups eventually also evolved herbivorous diets. The earliest and most basal probainognathian is the Middle Triassic (Anisian) aged ''Lumkuia'', from South Africa, though probainognathians would not become prominent until the mid Norian stage of the Late Triassic. Three groups survived the extinction at the end of Triassic: Tritheledontidae and Tritylodontidae, which both survived until the Jurassic—the latter even into the Cretaceous (''Montirictus'' and '' Xenocretosuchus'')—and Mammaliaformes, which includes the mammals. Phylogeny Below is a cladogram from Ruta, Botha-Brink, Mitchell and Benton (2013) showing one hypothesis of cynodont relationships: See also * Evolution of mammals * List of prehistoric mammals This is an incomplete list of prehistoric mammals. It does not include extant mam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adaptive Radiation
In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new environmental niches. Starting with a single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits. The prototypical example of adaptive radiation is finch speciation on the Galapagos ("Darwin's finches"), but examples are known from around the world. Characteristics Four features can be used to identify an adaptive radiation: #A common ancestry of component species: specifically a ''recent'' ancestry. Note that this is not the same as a monophyly in which ''all'' descendants of a common ancestor are included. #A phenotype-environment correlation: a ''significant'' association between environments and the morp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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