You might want to also point out that ONLY MAMMALS HAVE THREE EAR BONES. Ear bones are not present in any other group of critters -- reptiles do not have them, fish do not have them, birds do not have them and amphibians do not have them. As such, three ear bones are a very good indication that the deceased was a mammal and not a bird, reptile, fish or amphibian. Unfortunately, you seem hung up on mammary glands; do you have a boobie fixation?
Whether I do or I do not is irrelevant to this discussion. :)
The point is that there is nothing intrinisically necessary between the 3 earbones and mammary glands - the true definition of a mammal. There is an almost necessary connection between live birth and mammary glands because individuals not born from an egg are not able to feed themselves. We see though in the platypus that even this almost necessary connection is not true. So to say that the connection between mammary glands and 3 earbones is not necessary in animal fossils is a very valid statement. And this is the problem with paleontology - it will assume that any animal with 3 earbones is a mammal and any animal without 3 earbones is not a mammal. This can only be true if one also assumes the coevolution of different sytems at the same time. Such an assumption is of course utterly ridiculous and it is clearly laid to rest by our friend the platypus.