Taxonomical change

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David George
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Taxonomical change

Post by David George » Thu Mar 02, 2006 7:49 am

We know that the classification of chordates is Pisces,Amphibia,Reptilia,Aves,Mammalia.But we also know that mammals evolved from reptiles much before birds.So we are suppose to have the classification as Pisces,Amphibia,Reptilia,Mammalia,Aves To follow an evolutionary trend.

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Beetle
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Post by Beetle » Thu Mar 02, 2006 10:50 am

Classification is just our way of cathegorizing organisms. You can sort them in any way you want, desn`t matter, but you could never realisticaly make the natural order of evolution or phylogeny. It is common use to put them in this order Reptilia, Aves, Mammals cause we are antropocentric mammals and we must be in the end. :) It is not a problem as long as you have in mind that birds are also highly evolved but just in another line of evolution.
"In wildness is the preservation of the world" J. Hatfiled

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BillyJoe
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Post by BillyJoe » Thu Mar 02, 2006 11:03 am

The Evolution of Mammals


Before Mammals, there were fish which had the backbone and the skull, but pentadactyl limbs.

Fish first appeared around 510 million years ago. By about 350 million years ago the insects and plants had been dominating the land.

Eventually some fish transformed their fins into legs and in time they also developed lungs - legs for moving and lungs for breathing.

About 10 million years later reptiles started to differentiate from amphibians and diversity was well underway. Various groups evolved out of these early reptiles including crocodiles, dinosaurs and birds, but most importantly to us a strange group of animals called the Mammal-like Reptiles.

The Mammal-like Reptiles, or Therapsids first appeared about 285 million years ago near the begiining of the Permian which is well before the dinosaurs. They evolved quickly and many different groups arose. They were very successful until about the end of the Permian, about 245 million years ago, when something catastrophic affected the earth and nearly all of the species then living died out. New species evolved rapidly to fill this empty habitat, among them the first dinosaurs and a few million years later the first mammals.

The first mammal may never be known, but the Genus Morganucodon and in particular Morganucodon watsoni, a 2-3 cm (1 inch) long weasel-like animal whose fossils were first found in caves in Wales and around Bristol (UK), but later unearthed in China, India , North America, South Africa and Western Europe is a possible contender. It is believed to be between 200 MYA and 210 MYA. However Gondwanadon tapani reported from India on the basis of a single tooth in 1994 may be an earlier contender for the title, with a claimed date of 225 MYA.
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