What is cross species mutation and why have we never found fossils or anything to prove it's existance?

Question

A continuation of this YA question..

http://answers.yahoo.com/question/index?qid=20080831201753AAhoZA9

Answer 1

Species that are closely related - having been split from a common ancestor a relatively short time can cross breed if they contact each other.  Hybrids can be sterile but not always - and if they are not could possible lead to new species.

Mules are generally considered sterile but the odd case has occurred - about 1 in 100 - where a female mule has given birth after being impregnated by a horse.  The offspring looks more like a horse than a mule.

There is some DNA evidence that shows our ancestors split from the line that became chimpanzees then  experienced some crossbreeding (with fertile offspring) for quite some time before reaching a point where the lines were too different to breed.  

Answer 2

Ever seen a mule? Cross species mutation between a horse and a donkey.

I don't remember his name, but some scientist awhile back cross bred many animals that gave birth to very bizarre offspring. The thing is that a cross bred animal cannot reproduce, it is impossible for a mule to get pregnant.

Answer 3

Just where are you getting this information? The previous poster is correct in referring to mules and botanists cross-pollinate plants all the time.