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It has to do with the evolutionary tree. Shortly after the first reptiles appeared they split into synapsids and sauropsids. Mammals eventually branched off from the synapsid reptiles. After synapsid reptiles went extinct, mammals were left as the only synapsids.
Meanwhile the sauropsids diversified into a number of different groups including dinosaurs and the ancestors of all modern reptiles. Later on birds emerged as a branch of the dinosaurs.
In summary: mammals are synapsids while birds and modern reptiles are sauropsids.
What else can I help you with?
Are mammals related to birds?
Mammals are distantly related to birds. Oddly, if you look at an evolutionary tree, birds are actually more closely related to reptiles than they are to mammals.
Are dinosaurs the oldest mammals?
No. Dinosaurs were not mammals. They were more closely related to birds and modern reptiles than they were to mammals.
Did mammals evolve from dinosaurs?
No. Mammals evolved from synapsid reptiles, a group not closely related to dinosaurs. Dinosaurs are more closely related to modern reptiles and birds than they are to mammals.
Are animals related to birds?
Birds are more closely related to reptiles than they are to mammals. Birds, reptiles, and mammals all belong to a group of vertebrates called amniotes, which split off from amphibians. Amniotes split into two groups soon after they evolved: true reptiles and synapsids. Mammals are the only living synapsids today. Dinosaurs branched off from the reptiles and birds then evolved from the dinosaurs.
Do mammals have gills or lungs?
Mammals have lungs, as do amphibians, reptiles, and birds. Fish are the only chordates that have gills rather than lungs.
Is an egret a mammal or a reptile?
Birds are neither mammals, nor reptiles. They are an entirely different branch of evolution. However, they are more closesly related to reptiles, which they descended from. Their evolution from reptiles caused them to resemble mammals.
Do Marsupials share characteristics with other animals from other groups?
Marsupials are mammals, so share all features with other mammals. As well, they are vertebrates, so share the characteristic of having a backbone with birds, fish, reptiles and amphibians. Like birds and reptiles, mammals breathe via lungs (rather than gills), and like birds, they are warm-blooded.
Why aren't dinosaurs mammals?
Dinosaurs and mammals evolved from two separate branches of reptiles. Mammals evolved from synapisid reptiles (all of which are not extinct) while dinosaurs along with the modern branches of reptiles evolved from sauropsids. So dinosaurs are more closely related to modern reptiles than they are to mammals. In more recent years scientist tend to agree that birds are in fact a surviving branch of dinosaurs.
What classification of animal lays eggs on land and has lungs other than birds reptiles or mammal?
There is no such classification. However, monotremes are a sub-classification of mammals, and include the platypus and the echidna. They are egg-laying mammals.
compare and contrast the way birds and mammals reproduce?
birds are different than mammals
Why is a bird not a mammal?
Birds are not considered mammals because they do not feed their young milk and because they have feathers instead of fur. Birds lay eggs while most mammals give live birth. Birds are also distinguished by having beaks and a rather intricate and unique respiratory system. In terms of evolution, birds are more closely related to modern reptiles than they are to mammals.
Are birds more related to lizards than turtles?
In terms of lineage, yes. Birds are descended from dinosaurs, which, along with lizards, belong to a group of reptiles called diapsids. Turtles come from a separate group of reptiles called anapsids.
