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Eutherian
Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from non-eutherians by various phenotypic traits of the feet, ankles, jaws and teeth. All extant eutherians lack epipubic bones, which are present in all other living mammals (marsupials and monotremes). This allows for expansion of the abdomen during pregnancy, though epipubic bones are present in many primitive eutherians. Eutheria was named in 1872 by Theodore Gill; in 1880, Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia. The earliest unambiguous eutherians are known from the Early Cretaceous Yixian Formation of China, dating around 120 million years ago. Two tribosphenic mammals, '' Durlstodon'' and '' Durlstotherium'' from the Berriasian age (~145–140 million years ago) of the Ear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Marsupial
Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a relatively undeveloped state and then nurtured within a pouch on their mother's abdomen. Extant marsupials encompass many species, including Kangaroo, kangaroos, Koala, koalas, Opossum, opossums, Phalangeriformes, possums, Tasmanian devil, Tasmanian devils, Wombat, wombats, Wallaby, wallabies, and Bandicoot, bandicoots. Marsupials constitute a clade stemming from the last common ancestor of extant Metatheria, which encompasses all mammals more closely related to marsupials than to Placentalia, placentals. The evolutionary split between placentals and marsupials occurred 125-160 million years ago, in the Middle Jurassic-Early Cretaceous period. Presently, close to 70% of the 334 extant marsupial species are concentrated on the Australian ... [...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 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. Placentalia represents the only living group within Eutheria, which contains all mammals that are more closely related to placentals than they are to marsupials. 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microtherulum
''Microtherulum'' is an extinct genus of eutherian mammal known from the Early Cretaceous Jiufotang Formation of China. It is one of the earliest and most primitive eutherians. Description The genus is known from a mostly complete skeleton, including a well preserved skull, which is about long. The ear, which is among the best known in basal eutherians, is microtype, adapted for hearing high-frequency sounds. The dental formula is 5 incisors, 1 canine, 5 premolars and 3 molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ... in the each half of the upper jaw, and 4 incisors, 1 canine, 5 premolars and 3 molars in each half of the lower jaw, which is typical for basal eutherians. Phylogeny ''Microtherulum'' has been placed close to the base of Eutheria. References {{Taxonbar, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Juramaia
''Juramaia'' is an extinct genus of a therian mammal, possibly a very basal eutherian mammal, known from the Late Jurassic ( Oxfordian stage) or Early Cretaceous deposits of western Liaoning, China. It is a small shrew-like mammal weighing around . Discovery ''Juramaia'' is known from the holotype BMNH PM1343, an articulated and nearly complete skeleton including incomplete skull preserved with full dentition. It was collected in the Daxigou site, Jianchang, from the Tiaojishan Formation dated at about . It was first named by Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng and Qiang Ji in 2011 and the type species is ''Juramaia sinensis''. Classification The discovery of ''Juramaia'' provides new insight into the evolution of placental mammals by showing that their lineage diverged from that of the marsupials 35 million years earlier than previously thought. Furthermore, its discovery fills gaps in the fossil record and helps to calibrate modern, DNA-based methods of dating the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Durlstotherium
''Durlstotherium'' is an extinct genus of mammal from the Early Cretaceous. It contains a single species, ''Durlstotherium newmani''. The type specimen was found in Durlston Bay, Dorset, after which the genus was named. ''D. newmani'' was named after a British pub landlord, Charlie Newman. ''Durlstotherium'' and two of its contemporaries, '' Tribactonodon'' and '' Durlstodon'', had tribosphenidan (three-cusped) molars, which are an advanced characteristic among eutheria Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of Placentalia, placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians ...n mammals and suggest that the group emerged earlier than the Early Cretaceous. References {{Taxonbar, from=Q42898185 Prehistoric eutherians Fossil taxa described in 2017 Berriasian genera Early Cretaceous mammals of Europe Prehistoric mammal genera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epipubic Bone
Epipubic bones are a pair of bones projecting forward from the pelvic bones of modern marsupials, monotremes and fossil mammals like multituberculates, and even basal eutherians (the ancestors of placentals, who lack them). They first occur in non-mammalian cynodonts such as tritylodontids, suggesting that they are a synapomorphy between them and Mammaliformes. They were first described as early as 1698, but to date, their function(s) remain unresolved. Epipubic bones are often called ''marsupial bones'' because they support the mother's pouch in modern marsupials ("''marsupium''" is Latin for "pouch"). Function Some writers have suggested that the epipubic bones are a part of a kinetic link stretching from the femur on one side, to the ribs on the opposite side. This linkage is formed by a series of muscles: Each epipubic bone is connected to the femur by the pectineus muscle, and to the ribs and vertebrae by the pyramidalis, rectus abdominis, and external and inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Durlstodon
''Durlstodon'' is a genus of extinct mammal from the Early Cretaceous of Southern England. It contains a single species, ''Durlstodon ensomi'', which is known from molars found in the Berriasian Lulworth Formation of Durlston Bay, Dorset, after which the genus was named. The species name honours Paul Ensom, discoverer of many fossil mammals from Lulworth. ''Durlstodon'' and two of its contemporaries, '' Tribactonodon'' and ''Durlstotherium'', had tribosphenidan (three-cusped) molars, which are an advanced characteristic among eutheria Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of Placentalia, placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians ...n mammals and suggest that the group emerged earlier than the Early Cretaceous. References {{Taxonbar, from=Q42860812 Prehistoric eutherians Fossil taxa described in 2017 Berriasian genera Ear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theria
Theria ( or ; ) is a scientific classification, subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the Placentalia, placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes and various extinct mammals evolving prior to the common ancestor of placentals and marsupials. Characteristics Therians give birth to live young without a shelled egg (biology), egg. This is possible thanks to key proteins called Syncytin-1, syncytins which allow exchanges between the mother and its offspring through a placenta, even Marsupial#Reproductive system, rudimental ones such as in marsupials. Genetic studies have suggested a viral origin of syncytins through the Endogenous retrovirus, endogenization process. The marsupials and the placentals evolved from a common therian ancestor that gave live birth by suppressing the mother's immune system. While the marsupials continued to give birth to an underdeveloped fe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Northern Treeshrew
The northern treeshrew (''Tupaia belangeri'') is a treeshrew species native to Southeast Asia. In 1841, the German zoologist Johann Andreas Wagner first used the specific name ''Cladobates belangeri'' for treeshrews that had been collected in Pegu during a French expedition to Southeast Asia. These specimens were described by Isidore Geoffroy Saint-Hilaire in 1834 in whose opinion they did not differ sufficiently from '' Tupaia tana'' to assign a specific rank. Characteristics Results of a telemetry study involving northern treeshrews showed that their body temperature varies from during the night to during the day. This difference is larger than in other endotherms, and indicates that the circadian rhythms of body temperature and locomotor activity are synchronized. Adults weigh . The maximum longevity of the northern treeshrew is 11 years. Besides humans, the northern treeshrew is the only mammal known to willingly consume spicy food. This is due to a genetic mutation r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monotreme
Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. Although they are different from other living mammals in that they lay eggs, female monotremes are like other mammals in that they nurse their young with milk. Monotremes have been considered by some authors to be members of Australosphenida, a clade that contains extinct mammals from the Jurassic and Cretaceous of Madagascar, South America, and Australia, but this categorization is disputed and their taxonomy is under debate. All extant species of monotremes are indigenous to Australia and New Guinea, although they were also present during the Late Cretaceous and Paleocene epochs in s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yixian Formation
The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. It is known for its exquisitely preserved fossils, and is mainly composed of basalts interspersed with siliciclastic sediments. Research history The potential importance of the Yixian Formation was initially recognized during the time the Empire of Japan occupied China's Rehe Province, Rehe ("Jehol") Province after the Defense of the Great Wall in 1933. Many Japanese scientists had noticed fossil remains of extinct fish and reptiles, possibly the champsosaurs. These initial fossil discoveries made by Japanese scientists vanished once World War II ended in 1945. By 1949, when administration of the area passed to the Chinese Communist Party and its leader Mao Zedong, the fossils of Yixian were studied only by Chinese scientists. It was not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tibia
The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects the knee with the ankle bones, ankle. The tibia is found on the anatomical terms of location#Medial, medial side of the leg next to the fibula and closer to the median plane. The tibia is connected to the fibula by the interosseous membrane of leg, forming a type of fibrous joint called a syndesmosis with very little movement. The tibia is named for the flute ''aulos, tibia''. It is the second largest bone in the human body, after the femur. The leg bones are the strongest long bones as they support the rest of the body. Structure In human anatomy, the tibia is the second largest bone next to the femur. As in other vertebrates the tibia is one of two bones in the lower leg, the other being the fibula, and is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
