Subject: Were the protomammals from the Mesozioc era born as reptiles or mammals

Were the protomammals from the Mesozioc era born as reptiles or mammals
We watched a program called "Prehistoric Journey" that the Denver 
NaturalHistory Museum produced.  They talked about protomammals that
 evolved at the end of the Mesozoic Era.  They described them as part 
mammal and part reptile.  Do you know if they were born as reptiles 
or mammals?  Can you give us any other information on this species?
This is the first time we've ever heard of them and we can't find any
information on them. We're sorry, we haven't tried a web search yet.
Thank you for any light you can shed on this odd species.

Re:Were the protomammals from the Mesozioc era born as reptiles or mammals