Megazostrodon
2013229
222462958
2008-06-29T13:42:33Z
FunkMonk
4280259
{{Taxobox
| name = ''Megazostrodon''
| fossil_range = [[Late Triassic]] to Early [[Jurassic]]
| image = Megazostrodon.jpg
| image_width = 250px
| image_caption = ''Megazostrodon'' model, Natural History Museum, London
| regnum = [[Animal]]ia
| phylum = [[Chordata]]
| subphylum = [[Vertebrata]]
| unranked_classis = [[Amniota]]
| classis = [[Synapsida]]
| unranked_ordo = [[Mammaliaformes]]
| familia = '''Megazostrodontidae'''
| familia_authority = Gow, [[1986]]
| genus = '''''Megazostrodon'''''
| genus_authority = Crompton & Jenkins, [[1968]]
}}
'''''Megazostrodon''''' is an extinct [[Mammaliaformes|Mammaliaform]], widely accepted as being one of the first [[mammal]]s, appearing in the fossil record approximately 200 million years ago.<ref>[http://palaeo.gly.bris.ac.uk/communication/mcgowan/MAMS Fur and Fangs: Mammal Origins]. Palaeobiology and Biodiversity Research Group, University of Bristol.</ref> It did have some non-mammalian characteristics<ref>''some should be mentioned''.</ref> but they were minor enough to be able to say that this animal is likely to represent the final stage of the transition between [[cynodont]], or "mammal-like" [[reptiles]] and true mammals.<ref>[http://www.tandf.co.uk/JOURNALS/pdf/ghbi_06_01_02.pdf ''Historical Biology''. 1992, vol. 6 p.186]</ref>
==Characteristics==
''Megazostrodon'' was a small, furry,<ref>Its furriness is extrapolated from the fact that its skeletal morphology implies a warm-blooded animal with a high metabolism, and warm-blooded animals are covered with insulatiing features like feather, down, or hair in mammals.</ref> [[shrew]]-like animal between 10 and 12 cm long which probably ate insects and small lizards. It is thought that it was [[nocturnal]] as it had a much larger brain<ref>[http://palaeo.gly.bris.ac.uk/communication/mcgowan/MAMS Fur and Fangs: Mammal Origins]. Palaeobiology and Biodiversity Research Group, University of Bristol.</ref> than its [[cynodont]] relatives and the enlarged areas of its brain were found to be those that process sounds and smells. This was probably in order to avoid being in competition with the reptiles or becoming prey to the [[dinosaur]]s.<ref>[http://adsabs.harvard.edu/abs/1976RSPTB.273..387J Smithsonian Science Abstract]</ref>
==Evolution==
''Megazostrodon'' is the only well-known genus of the family [[Megazostrodontidae]]. The other members of this family that are currently known to science are [[Indozostrodon]], [[Dinnetherium]], [[Wareolestes]] and [[Brachyzostrodon]]. The megazostrodontids used to be classified as members of a group of mammals called the [[Triconodont]]s, which are thought to have evolved from a specific group of reptiles (the [[cynodont]]s or 'mammal-like reptiles’)<ref name="Mammology">[http://www.shsu.edu/~bio_mlt/mammalogy1.html Mammology] Sam Houston State University.</ref> during the late [[Triassic]] and early [[Jurassic]] periods. However, recent classifications consider the megazostrodontids to be mammaliaforms just outside the Mammalia proper, while the triconodonts remain in the (crowngroup) Mammalia. One must keep in mind that the distinction between true mammals and mammaliaformes is purely a cladistic and phylogenetic one: mammaliaforms ''are'' mammals in every other way.
These early mammals developed many traits which were to make them well-suited for a very active lifestyle. They developed four types of teeth<ref name="FMA">[http://www.stellar.co.nz/tl10.html First Mammals Appear]</ref> (as opposed to the uniform teeth of the reptiles) , [[incisors]], [[canine tooth|canines]], [[premolars]] and [[molars]], which enabled them to chew and therefore process their food more thoroughly than their reptilian cousins. Their skeletons changed so that their limbs were more flexible (they became less laterally splayed,<ref>[http://www.shsu.edu/~bio_mlt/mammals.html Mammalian Characteristics]. Sam Houston State University.</ref> allowing for faster forward motion) and they developed a shorter ribcage and larger lungs<ref name="FMA">[http://www.stellar.co.nz/tl10.html First Mammals Appear]</ref> to allow for faster [[Respiratory system|respiration]]. The structure of their jaw bones changed, the lower jaw becoming a single bone — the [[dentary]] (as opposed to the seven different bones found in reptilian lower jaws). The other bones which once made up the jaw moved to the middle ear<ref>[http://palaeo.gly.bris.ac.uk/communication/mcgowan/MAMS Fur and Fangs: Mammal Origins]. Palaeobiology and Biodiversity Research Group, University of Bristol.</ref> to create a hearing system.
Probably the most important aspect of change in the evolution that led to these first mammals was that their direct ancestors (the [[cynodonts]]) had become [[warm-blooded]]. This meant that they relied on the food they ate to help sustain their body temperature rather than depending on their surrounding environment, which enabled them to maintain higher activity levels during the day than reptiles could (as reptiles frequently have to perform temperature regulation activities such as sun basking and seeking shade) and even to become nocturnal — a major advantage in a world where most predators were active during the day.
==Reproduction==
''Megazostrodon'' suckled their young,{{Fact|date=August 2007}} which suggests a higher degree and longevity of parental care than is generally the case amongst reptiles (although there are thought to have been exceptions to this as there certainly are today; most reptiles are independent from birth and are often actually seen as prey items to their parents). This parental care would have provided higher nutrition levels and therefore speedy growth, and more opportunity for education of the youngsters— having to rely less heavily on hard-wired natural instinct. This method of raising young allows for a lower infant mortality rate and higher population increase.
Despite all the mammalian traits that ''Megazostrodon'' acquired, it is thought that they still laid leathery eggs like their reptilian cousins, similar to the extant [[monotreme]]s. Live birth and the [[placenta]] would be later evolutions for mammals.
==Discovery==
''Megazostrodon rudnerae'' was first discovered in [[Africa]] by Ione Rudner (whose surname was given to the animal’s [[specific name]]) in 1966.<ref>[http://dml.cmnh.org/1999Dec/msg00290.html Dinosaur Mailing List]</ref> It was, however, first described by A.W. Crompton and F.A. Jenkins Jr in 1968.<ref>Crompton and Jenkins, "Molar occlusion in late Triassic mammals", ''Biological Review'', '''43''' 1968:427-458.</ref>
Its name means, literally, ‘Rudner’s large girdle tooth’ (from the Greek ''mega''-large, ''zostros''-girdle and ''odon''-tooth — referring to the large external cingula, or ridges of the upper molars).
==See also==
* [[Evolution of mammals]]
==Notes==
{{reflist|2}}
==External links==
*[http://palaeo.gly.bris.ac.uk/communication/mcgowan/MAMS FUR AND FANGS-MAMMAL ORIGINS]
*[http://www.stellar.co.nz/tl10.html First mammals appear]
*[http://www.bowdoin.edu/~dbensen/Dinosaurs/Megazostrodonrudnerae.html Picture]
*[http://dino.lm.com/images/display.php?id=2883 Picture 2]
*[http://members.iinet.net.au/~drage/index.php?p=p15 First Mammals and Plate Tectonics]
*[http://www.shsu.edu/~bio_mlt/mammalogy1.html A brief history of mammalogy.]
*[http://books.google.com/books?vid=ISBN0632056142&id=PQuKO7xqjNQC&pg=RA2-PA300&lpg=RA2-PA300&ots=sDDQLJnMXr&dq=megazostrodon&sig=ln8Vvn1epsJ5aUsKgOlSENooeJM#PRA2-PA299,M1 Vertebrate paleontology-Michael J. Benton.]
[[Category:Mammaliaformes]]
[[Category:Triassic mammals]]
[[Category:Jurassic mammals]]
[[Category:Prehistoric mammals of Africa]]
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