Also, let's not forget that creatures in D&D worlds mostly don't evolve. There is no such thing as evolution or natural selection in D&D settings, creatures are just created as they look now by gods, titans, primal energies, designers
.
Dragonborn were probably just created the way they are now, so the matter is not scientifical. There are no mammals, birds or reptiles in D&D, there are magical beasts, animals, dragons, aberrations, etc.
It is an aesthetical discussion. Are female dragonborn with boobs cool? Are hairy dragonborn cool?

Dragonborn were probably just created the way they are now, so the matter is not scientifical. There are no mammals, birds or reptiles in D&D, there are magical beasts, animals, dragons, aberrations, etc.
It is an aesthetical discussion. Are female dragonborn with boobs cool? Are hairy dragonborn cool?