Some mammals have what is called headgear, this headgear, is what we know as horns and antlers. Horns can be found in species like sheep, goats, bison , and cattle. These horns, branch out of the frontal bone of the skull, and are made of keratinized skin. Antlers are found in mammals like reindeer. Antlers are bone, and are shed annually.
Giraffes are another mammal which have horns.
These horns have the same structure as antlers. Rhinos too have head gear, but it does not grow from the skull. Rhino head gear is actually keratinized hair which has been fused together. Reproduction of mammals varies greatly between the different orders. Monotreme , are the only type of mammal which lay eggs, all other mammals give birth to their young live.