Why were the ancestors of the platypus so different?

Question

were they different because the ancestor ate different food or lived in a different enviroment?

Answer 1

Because they were only one of two MAMMALS that lay eggs.  They also produce milk for their young.  What is unique about the platypus is that it has retained a large overlap between two very different classifications, while later mammals lost the features of reptiles.

Here is a FASCINATING link to an article about the platypus.  This is recently learned information that  only came out last month.  Enjoy.

http://yubanet.com/scitech/Platypus-Geno...