Dryolestoidea
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Dryolestoidea
Dryolestida is an extinct order of mammals, primarily and possibly exclusively known from the Jurassic and Cretaceous. They are considered members of the clade Cladotheria, close to the ancestry of therian mammals. It is also believed that they developed a fully mammalian jaw and also had the three middle ear bones. Most members of the group, as with most Mesozoic mammals, are only known from fragmentary tooth and jaw remains. The taxonomic composition of the group is contested. Aside from the uncontroversial Dryolestidae and the possibly paraphyletic Paurodontidae, which were small insectivores, known from the Middle Jurassic to Early Cretaceous of Laurasia, the Meridiolestida, a diverse group of mammals including both small insectivores and mid-large sized herbivores known from the Late Cretaceous to Miocene of South America and possibly Antarctica, are also often included. However, in many phylogenetic analyses, Meridiolestida are recovered as an unrelated group of clado ...
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Cladotheria
Cladotheria is a clade (sometimes ranked as a legion) of mammals. It contains modern therian mammals (marsupials and placentals) and several extinct groups, such as the dryolestoids, amphitheriids and peramurids. The clade was named in 1975 by Malcolm McKenna. In 2002, it was defined as a node-based taxon containing "the common ancestor of dryolestids and living therians, plus all its descendants". A different, stem-based definition was given in 2013, in which Cladotheria contains all taxa that are closer to ''Mus musculus'' (the house mouse) than to the "symmetrodont" '' Spalacotherium tricuspidens''. Description Early cladotherians can be distinguished from other mammals by a number of derived traits (apomorphies). Their teeth differed from those of the "symmetrodonts" by the evolution of a talonid shelf ( hypoflexid) on the lower molars, which occluded with the paracone of the corresponding upper molars. A true talonid basin, allowing for the crushing and grinding of f ...
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Meridiolestida
Meridiolestida is an extinct clade of mammals known from the Cretaceous and Cenozoic of South America and possibly Antarctica. They represented the dominant group of mammals in South America during the Late Cretaceous. Meridiolestidans were morphologically diverse, containing both small insectivores such as the "sabretooth-squirrel" '' Cronopio,supplementary information
'' as well as the clade Mesungulatoidea/Mesungulatomorpha, which ranged in size from the shrew-sized '''' to the dog-sized '' Peligrotherium.'' ...
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Paurodontidae
Paurodontidae is a family of Late Jurassic to Early Cretaceous mammals in the order Dryolestida. Remains of paurodontids have been found in the United States, Britain, Portugal, and Tanzania. The group likely represents a paraphyletic group of basal non dryolestid dryolestidans. '' Paurodon'' has been suggested to have been a specilast feeder on earthworms due to the morphology of its teeth closely resembling that of the golden mole genus ''Amblysomus ''Amblysomus'' (also narrow-headed golden mole or South African golden mole) is a genus of the golden mole family, Chrysochloridae, comprising five species of the small, insect-eating, burrowing mammals endemic to Southern Africa. All five spec ...''.A.O. Averianov and T. Martin (2015). "Ontogeny and taxonomy of Paurodon valens (Mammalia, Cladotheria) from the Upper Jurassic Morrison Formation of USA" (PDF). Proceedings of the Zoological Institute of the Russian Academy of Sciences 319 (3): 326–340. References Dryolestida ...
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Mesungulatids
Mesungulatidae is an extinct clade of meridiolestidan dryolestoid mammals from the Late Cretaceous of South America and possibly other Gondwannan landmasses. They are particularly notable for their ecological speciation and large size. Characteristics Most mesungulatids are generally large animals, making them inherently distinctive from other groups. Specific synapomorphies include a strong precingulum and postcingulum on the upper molars - which are extended lingually but do not meet around the paracone - three cusps on the lower stylar shelf, an absent metacone and rectangular lower molars. They are thought to have had a somewhat transverse mastication, like docodonts and modern ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, ...s. Compared to other dryolestoids thei ...
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Brandoniidae
Dryolestidae is an extinct family of Mesozoic mammals, known from the Middle Jurassic to the Early Cretaceous of the North Hemisphere. The oldest known member, '' Anthracolestes'', is known from the Middle Jurassic Itat Formation of Western Siberia, but most other representatives are known from the Late Jurassic of North America and the Late Jurassic and Early Cretaceous of Europe. Most members are only known from isolated teeth and jaw fragments. Like many other groups of early mammals, they are though to have been insectivores. They are generally classified in Cladotheria, meaning that they are considered to be more closely related to marsupials and placentals than to monotremes. They are placed as part of the broader Dryolestida, which also includes the (possibly paraphyletic) Paurodontidae, and also sometimes the South American-Antarctic Meridiolestida, which are often considered unrelated cladotherians. Dyolestidae is not based on a phylogenetic definition, but instead on ...
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Dryolestidae
Dryolestidae is an extinct family of Mesozoic mammals, known from the Middle Jurassic to the Early Cretaceous of the North Hemisphere. The oldest known member, '' Anthracolestes'', is known from the Middle Jurassic Itat Formation of Western Siberia, but most other representatives are known from the Late Jurassic of North America and the Late Jurassic and Early Cretaceous of Europe. Most members are only known from isolated teeth and jaw fragments. Like many other groups of early mammals, they are though to have been insectivores. They are generally classified in Cladotheria, meaning that they are considered to be more closely related to marsupials and placentals than to monotremes. They are placed as part of the broader Dryolestida, which also includes the (possibly paraphyletic) Paurodontidae, and also sometimes the South American-Antarctic Meridiolestida, which are often considered unrelated cladotherians. Dyolestidae is not based on a phylogenetic definition, but instead on t ...
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Henkelotherium
''Henkelotherium'' is an extinct genus of dryolestidan mammal from the Late Jurassic (Kimmeridgian) Camadas de Guimarota, in Portugal. Unlike many other Jurassic mammals, it is known from a largely complete skeleton, and is thought to have had an arboreal lifestyle. Description The skull of ''Henkelotherium'' is long, and presacral body length is . This suggest a weight of about . Paleobiology Primitive characters of ''Henkelotherium'' (e.g. asymmetric condyles of the femur) indicate that this species had a mode of locomotion similar to tree shrews and opossums. The small size of ''Henkelotherium'' and elongated tail made it suited to an arboreal lifestyle and capable of climbing trees, a notion supported by the paleoecological reconstruction of the Guimarota ecosystem indicating a densely vegetated environment. Taxonomy In cladistic analyses, ''Henkelotherium'' has been considered closely related to Dryolestidae, either as a part of that group, or as closely related b ...
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Plesiomorphy
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and synapomorphy, all mean a trait shared between species because they share an ancestral species. Apomorphic and synapomorphic characteristics convey much information about evolutionary clades and can be used to define taxa. However, plesiomorphic and symplesiomorphic characteristics cannot. The term ''symplesiomorphy'' was introduced in 1950 by German entomologist Willi Hennig. Examples A backbone is a plesiomorphic trait shared by birds and mammals, and does not help in placing an animal in one or the other of these two clades. Birds and mammals share this trait because both clades are descended from the same far distant ancestor. Other clades, e.g. snakes, lizards, turtles, fish, frogs, all have backbones and none are either birds nor ...
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Tooth Enamel
Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, cementum, and dental pulp. It is a very hard, white to off-white, highly mineralised substance that acts as a barrier to protect the tooth but can become susceptible to degradation, especially by acids from food and drink. Calcium hardens the tooth enamel. In rare circumstances enamel fails to form, leaving the underlying dentin exposed on the surface. Features Enamel is the hardest substance in the human body and contains the highest percentage of minerals (at 96%),Ross ''et al.'', p. 485 with water and organic material composing the rest.Ten Cate's Oral Histology, Nancy, Elsevier, pp. 70–94 The primary mineral is hydroxyapatite, which is a crystalline calcium phosphate. Enamel is formed on the tooth while the tooth develops withi ...
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Rostrum (anatomy)
Rostrum (from Latin ', meaning ''beak'') is a term used in anatomy for a number of phylogenetically unrelated structures in different groups of animals. Invertebrates * In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes. It is generally a rigid structure, but can be connected by a hinged joint, as seen in Leptostraca. * Among insects, the rostrum is the name for the piercing mouthparts of the order Hemiptera as well as those of the snow scorpionflies, among many others. The long snout of weevils is also called a rostrum. * Gastropod molluscs have a rostrum or proboscis. * Cephalopod molluscs have hard beak-like mouthparts referred to as the rostrum. File:Washington DC Zoo - Macrobrachium rosenbergii 6.jpg, Crustacean: the rostrum of the shrimp '' Macrobrachium rosenbergii'' is serrated along both edges. File:Gminatus australis with Beetle.jpg, Insect: assassin bug piercing its prey with its rostrum File:Architeuthis beak.jpg, Cephal ...
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Arboreal Locomotion
Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose numerous mechanical challenges to animals moving through them and lead to a variety of anatomical, behavioral and ecological consequences as well as variations throughout different species.Cartmill, M. (1985). Climbing. In ''Functional Vertebrate Morphology'', eds. M. Hildebrand D. M. Bramble K. F. Liem and D. B. Wake, pp. 73–88. Cambridge: Belknap Press. Furthermore, many of these same principles may be applied to climbing without trees, such as on rock piles or mountains. Some animals are exclusively arboreal in habitat, such as the tree snail. Biomechanics Arboreal habitats pose numerous mechanical challenges to animals moving in them, which have been solved in diverse ways. These challenges include moving on narrow branches, mo ...
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Last Common Ancestor
In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The term is also used in reference to the ancestry of groups of genes (haplotypes) rather than organisms. The MRCA of a set of individuals can sometimes be determined by referring to an established pedigree. However, in general, it is impossible to identify the exact MRCA of a large set of individuals, but an estimate of the time at which the MRCA lived can often be given. Such ''time to most recent common ancestor'' (''TMRCA'') estimates can be given based on DNA test results and established mutation rates as practiced in genetic genealogy, or by reference to a non-genetic, mathematical model or computer simulation. In organisms using sexual reproduction, the ''matrilineal MRCA'' and ''patrilineal MRCA'' are the MRCAs of a given population c ...
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