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Anonymous
>>482822 Best Answer - Chosen by Asker No, birds are not mammals. Modern systematics (phylogenetic systematics or cladistics) define all groups by shared derived characters - synapomorphies-. Thus, mammals as a crown group (that is, considering only all the living species and their latest common ancestor) are tetrapod vertebrates with fur, with lower jaw formed by a single bone (the dentary), middle ear with three ossicles, and which nurse their young with milk. There are more characteristics of the group, but any animal that fulfills these conditions is a mammal. The crown-group of birds (Aves) includes vertebrates with feathers, with a beak covered in a horny sheath, lacking teeth, and which lay eggs with a special shell mineralization type; also they have several skeletal specializations. However, many of these traits are shared with non-avian archosaur reptiles (especially dinosaurs) - which is why I mentioned the crown-group. These characteristics of birds and mammals are mutually exclusive. The last common ancestor of these groups was a basal Paleozoic amniote, because the reptile line that gave origin to mammals (the Synapsida) was already differentiated by the end of the Paleozoic, whereas birds evolved within the Archosauria (Sauropsida diapsid reptiles) in the Mesozoic Age.
yahoo answers ;P
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