Transitions Of Reptiles To Mammals Essays -- essays research papers

Transitions of Reptiles to Mammals     A long long time ago, in a galaxy not too far away, was a mid nettle blueplanet called Earth, and on this world not a genius mammal lived. However a lotof time has past since and then and we now have lots of furry creatures that arecollectively called mammals. How did they get their? Where did they come from?These are the kinds of questions that led me to my subject of choice. I will purpose to provide examples, using specific transitional fossils, to show thatmammals have evolved from a group of reptiles and were simply not placed here by mystical forces.     Before I begin, I would like to define some scathe so that nobody getsleft in the dust. The term transitional fossil can be used in conjunction withthe term ecumenical lineage, together they help explain the how one species becameanother."General lineage"This is a sequence of similar genera or families, linking an older to a veryunlike younger group. Each step in the sequence consists of some fossils that wreak certain genus or family, and the whole sequence often covers a cut across oftens of millions of years. A lineage like this shows obvious intermediates forevery major morphological change, and the fossils occur roughly (but often notexactly) in the expected purchase order. However, commonly there are still gaps betweeneach of the groups. Sometimes the soulfulness specimens are not thought to bedirectly ancestral to the next-youngest fossils (e.g. they whitethorn be "cousins"" or"uncles" rather than "parents"). However they are assumed to be closely relatedto the actual ancestor, since the have similar intermediate characteristics.Where Does It altogether Begin ?     Mammals were derived during the Triassic Period ((from 245 to 208million years ago) It began with relatively agile and wet conditions, but as itprogressed conditions became increasingly hot and dry.) from members of thereptilian order Therapsida. The therapsids, members of the subclass Synapsida(sometimes called the mammal-like reptiles),generally were unimpressive inrelation to other reptiles of their time. Synapsids were present in theCarboniferous Period (about 280 to 345 million years ago) and are one of the soonest known reptilian groups. Although therapsids were primarily p... ...ng the origin of major new adjustive types. To simplify definitions and toallow the strict delimitation of the Mammalia, some authors have suggestedbasing the bound on a single character, the articulation of the jaw betweenthe dentary and squamosal bones and the attendent movement of accessory jawbones to the middle ear as auditory ossicles. The use of a single characterallows the placement in a logical classification of numerous fossil species,other mammalian. characters of which, such(prenominal) as the degree of endothermy andnursing of young and the condition of the internal organ s, probably never willbe evaluated. It must be recognized, however, that if the advanced therapsidswere vital today, taxonomists would be hard-put to decide which to place in theReptilia and which in the Mammalia.ReferencesCarroll, R. 1988. vertebrate Paleontology and Evolution. W.H. Freeman andCo., New YorkGingerich, P.D. 1977. Patterns of Evolution in the Mammalian fossil Record.Elsevier Scientific Pub. Co.Gingerich, P.D. 1985. Species in the Fossil Record Concepts, Trends, andTransitions. Paleobiology.Rowe, T. 1988. Definition, Diagnosis, and Origin of Mammalia. J. Vert.Paleontology.