Question: those animals that there ears are visible tend to produce baby where as unvisible ear animals produce eggs, is that true?

Ceri-Wyn Thomas answered on 17 Jun 2010:

That’s very perceptive! Um….well it’s generally the case that mammals give birth to live young (as opposed to eggs). Mammals’ ears are very much visible since they provide a good warning system for approaching predators and they don’t have to contend with being submerged in water for long periods of time like aquatic animals (although even hippos have little ears and they LOVE being in water!). Reptiles, amphibians, birds etc produce eggs generally since their life habits are different- they are either fully aquatic and/or they have to leave their young for long periods of time to find food (this is especially true for birds) so laying eggs is a much better strategy for caring for their young. So really- they have evolved strategies to cope with their environments AND their bodies have evolved to cope with the same environments. Reptile’s ears are often internal probably because of their evolutionary history of evolving from water-loving amphibians and birds are related to reptiles! Having “outie” ears in both these cases would make them a lot less hydro/aerodynamic. Mammals don’t need to worry about that.

So this pattern you’ve noticed is down to evolution and the nature of the environments these animals have evolved in. Not having ears DOESN’T mean you will always lay eggs and vice versa: There are ALWAYS exceptions to this rule- the duck billed platypus (a mammal) lays EGGS! But then it is semi-aquatic and you can’t see it’s ears!