RAZD replied as if he understood your post, but you didn't quote anything and I didn't understand it, so please let me seek clarification.
That the thread is done? Something else?
...but there are plenty below the reptiles...
Plenty of what below the reptiles? Once I know that I can try to answer this:
...that don't seem to be represented.
But the main question is probably whether there are reptiles and the same mammals above this mammal layer.
The article was about a sequence of layers containing mammal fossils - when you say "this layer," which layer are you referring to?
Generally I can say that the duration in time that species persist varies widely. Some species might span many geologic ages, some might not. So answering your question in this general context, some mammal species might persist through many ages above the "mammal layer" where first found, some might not.