What are the differences between animals belonging to the Aves group and those in the mammalian group?

 In aves, body is covered with feathers; while in mammals, body is covered with hairs. 

 Mammary glands are absent in aves while present in mammals. 

 Forelimbs of aves are modified into wings which is not the case in mammals. 

 Aves are oviparous, while most of the mammals are viviparous.

In aves, body is covered with feathers; while in mammals, body is covered with hairs. Mammary glands are absent in aves. Forelimbs of aves are modified into wings which is not the case in mammals. Aves are oviparous, while most of the mammals are viviparous.