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The cleavage stages of marsupial development are very variable between groups and aspects of marsupial early development are not yet fully understood. An infant marsupial is known as a joey . Marsupials have a very short gestation period—usually between 12.5 and 33 days, [ 41 ] but as low as 10.7 days in the case of the stripe-faced dunnart ...
Due to the fact that placental mammals and marsupials nourish their developing embryos via the placenta, the ovum in these species does not contain significant amounts of yolk, and the yolk sac in the embryo is relatively small in size, in comparison with both the size of the embryo itself and the size of yolk sac in embryos of comparable developmental age from lower chordates.
The latter subclass is divided into two infraclasses: pouched mammals (metatherians or marsupials), and placental mammals (eutherians, for which see List of placental mammals). Classification updated from Wilson and Reeder's "Mammal Species of the World: A Taxonomic and Geographic Reference" using the "Planet Mammifères" website. [1]
A marsupial has a short gestation period, typically shorter than its estrous cycle, and gives birth to an underdeveloped newborn that then undergoes further development; in many species, this takes place within a pouch-like sac, the marsupium, located in the front of the mother's abdomen.
The maximum litter size is, therefore, eight, since marsupial young are attached to the teat during development, although two to four young per litter is a more typical number. The gestation period of peramelids is the shortest among mammals, at just 12.5 days, the young are weaned around two months of age, and reach sexual maturity at just ...
The pouch is a distinguishing feature of female marsupials and monotremes, [1] [2] [3] and rarely in males as well, such as in the yapok [4] and the extinct thylacine. The name marsupial is derived from the Latin marsupium, meaning "pouch". This is due to the occurrence of epipubic bones, a pair of bones projecting forward from the pelvis
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
In mammals, the term refers chiefly to the early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. [2] [4] The main stages of animal embryonic development are as follows: The zygote undergoes a series of cell divisions (called cleavage) to form a structure called a morula.