What animal has both characteristics of mammals and birds?

There is no animal that has both the characteristics of mammals and birds. They are two distinct classes of animals with very different evolutionary paths and characteristics.

Here's a breakdown of their key differences:

Mammals:

* Give birth to live young (viviparous)

* Nurse their young with milk produced by mammary glands

* Have fur or hair

* Warm-blooded (maintain a constant body temperature)

* Breathe air with lungs

* Four-chambered heart

* Have a diaphragm

* Typically have teeth

Birds:

* Lay eggs (oviparous)

* Have feathers

* Warm-blooded

* Breathe air with lungs

* Four-chambered heart

* Have a beak

* Have wings and most are capable of flight

While some animals may have some superficial similarities to both groups (like the platypus with its duck-like bill), they are still definitively classified as one or the other.

It's important to note that evolution is a complex process and some species may exhibit features that resemble other groups due to convergent evolution (where similar traits evolve independently in different lineages). However, the fundamental characteristics that define mammals and birds remain distinct.