Abstract Aim Although most reptiles are oviparous, viviparity is a common mode of reproduction in squamates and has evolved multiple times in different lineages. This embryotrophe is the maternal source of nutrition for the embryo after the yolk-sac has been consumed. C. Viviparous animals, like mammals, have internal fertilisation, and live births. The historical connection between viviparity and oviparity is indicated by rare cases of ovoviviparity, in which the embryo develops from an egg in the mother’s body and is nourished chiefly on substances stored in the egg itself, but also is secreted by the mother’s body and is freed of the egg covering, usually after the egg is laid. Like all mammals, they are endothermic, have hair, possess a single jaw bone, and have the diagnostic three-bone middle ear structure. Most mammals and some other animals are viviparous. This form of placentation is characterized by a highly erosive trophoblast capable of extensive remodeling of the uterine vasculature, thereby permitting the direct flow of maternal blood to the surface of trophoblast cells. Joshua R. Ginsberg, in Encyclopedia of Biodiversity (Second Edition), 2013. In bony fishes alone, viviparity has arisen independently at least 13 times, and in cartilaginous fishes at least 9 times. For species with a range of reported stages at oviposition, modal values (or if unavailable, range midpoints) were used. Among a very few frogs and salamanders, but several caecilians, the oviductal lining cells elaborate a nutrient material that the juveniles, hatched after their yolk is resorbed, ingest orally before birth, often using fetal teeth. New information about the genetics of placental development and maintenance, first found among mammals, but now also occurring in squamates and seahorses, indicates that a common genetic basis exists in all of these diverse vertebrates for intra-oviductal maintenance, especially placentae. Join the 2 Crores+ Student community now! Historically, an understanding of viviparity and its evolution in Old World chameleons (Chamaeleonidae) has lagged behind that of other squamate families. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the mother. Mathies and Andrews believe that these animals are able to support embryonic development to term within fully shelled eggs in oviducts and that the thinning of the eggshell may be a postviviparity event rather than a prelude to viviparity (Mathies and Andrews, 2000). Chondrichthyan eggs are non-buoyant and thus unsuited for pelagic environments, and as many chondrichthyans are physiologically limited in the number of eggs they can produce, the transition to viviparity is not thought to be associated with a significant loss in fecundity (Wourms and Lombardi, 1992). The main advantage of matrotrophic reproduction is that embryos can gain significant weight and size during their development, in comparison with solely yolk-sac nutrition. b. A recent review shows that matrotrophy (provision of nutrients to developing embryo during gestation), even among invertebrates, is not as rare as previously thought. Placentotrophy relies on evolution and development of structures that make the nourishment and respiration of the embryo in the reproductive tract possible and oviparity implies provision to the egg of nutrients in the form of yolk (lecithotrophy) and water necessary for the development until hatching. Retention of eggs in oviducts and maintenance through to a juvenile state seems to be easy to do. Zoology Giving birth to living offspring that develop within the mother's body. The term 'viviparity' and its adjective form 'viviparous' derive from the Latin vivus meaning "living" and pario meaning "give birth to". A gradual increase in the duration of oviductal egg retention, leading to viviparity, a gradual development in viviparous forms of a simple placenta that functions in gas exchange and water uptake, and a progressive reliance on the placenta as a means of supplying inorganic and organic nutrients for development, eventually leading to placentotrophy. In this type of nutrition, the egg case, a yellowish and thin membrane that surrounds the embryo throughout development, becomes filled early in the gestation with a large quantity (about one liter) of a clear yellowish fluid, embryotrophe. This pattern of “oviparous egg-retention” may be an intermediate evolutionary stage toward, Encyclopedia of Biodiversity (Second Edition), Strategies for Investigating Hemochorial Placentation, Reproductive and Developmental Toxicology (Second Edition), American Journal of Obstetrics and Gynecology, Knobil and Neill's Physiology of Reproduction (Fourth Edition), (1) Clades contain species in primitive, intermediate, and advanced evolutionary stages, (2) A continuum exists of developmental stages at parition among living species, (3) Viviparous and oviparous congeners are similar, (4) Recent origins of viviparity exhibit a bimodal distribution of parition stages, (7) A bimodal distribution of parition stages exists, but some species oviposit advanced eggs, (8) Facultative, oviparous egg-retention with intraoviductal development occurs, (9) Viviparous and oviparous congeners are similar. From Blackburn, D.G., 1995. Viviparity, retention and growth of the fertilized egg within the maternal body until the young animal, as a larva or newborn, is capable of independent existence. Ovoviviparity occurs when an animal has internal fertilisation and eggs are produced inside the female reproductive tract. Contrary to that conventional gradualistic model of evolution of viviparity in lizards and snakes, more than 100 clades of these groups have made transition from oviparity to true viviparity (Blackburn, 1995) and recent studies have failed to find intermediate forms between viviparous and oviparous species: Various phenotypic intermediates postulated by the gradualistic model are either scarce or unrepresented among known forms, including those in which viviparity has evolved at specific and subspecific levels …placentae and a degree of placentotrophy have evolved repeatedly as necessary correlates of viviparity, not as subsequent modifications. 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