Мегазостродон: жоғалып кеткен сүтқоректілер туысы

Extinct genus of mammaliaforms
Automatic taxobox
| fossil range =
| image = Megazostrodon sp. Natural History Museum London. jpg
| image upright = 1.1
| image caption = Megazostrodon model, Natural History Museum, London
| taxon = Megazostrodon
| authority = Crompton & Jenkins, 1968
| type species = Megazostrodon rudnerae
| type species authority = Crompton & Jenkins, 1968 Two species are known: M. rudnerae from the Early Jurassic of Lesotho and South Africa, and M. chenali from the Late Triassic of France.

The type species M. rudnerae was first discovered in 1966 in the Elliot Formation of Lesotho, southern Africa, by palaeontologist and archaeologist Ione Rudner. It was first described by A. W. Crompton and F. A. Jenkins Jr in 1968. A second species, M. chenali, was named in 2015 based on remains found in Saint Nicolas de Port, France. It is named after the French palaeontologist Emmanuel Chenal. Although considered a close relative of mammals, it did have some non mammalian characteristics inherited from its predecessors: the first two vertebrae (atlas and axis) were still unfused as in earlier cynodonts, and it only had three sacral vertebrae instead of the usual mammalian five. An interclavicle is also present, which is still present in monotremes but lost in the line leading to therian mammals.

Megazostrodon is the best known genus of the family Megazostrodontidae, part of the larger group Morganucodonta. The other members of this family that are currently known are Indozostrodon, Dinnetherium, Wareolestes and Brachyzostrodon. The megazostrodontids used to be classified as members of a group of mammals called the triconodonts, which are thought to have evolved from a specific group of cynodonts during the late Triassic and early Jurassic periods. However, recent classifications consider the megazostrodontids to be mammaliaforms outside of the stricter grouping of Mammalia proper, while the triconodonts remain within the mammalian crown group. These early mammaliaforms possessed many traits which made them well suited for an active lifestyle. They had a heterodont dentition consisting of four types of teeth: incisors, canines, premolars and molars, as opposed to the uniform (homodont) teeth of most reptiles. This enabled them to chew and therefore process their food more thoroughly than their reptilian cousins. There is evidence that the movement of the mandible allowed a shearing action to chew food. Their skeletons changed so that their limbs were more mobile, being less laterally splayed, and allowing faster forward motion. They had a short ribcage and large lungs, which allowed efficient respiration.

Like placentals and possibly Erythrotherium, Megazostrodon is unique among mammaliaforms in lacking epipubic bones. It is likely that Megazostrodon, like the modern monotremes, laid eggs.