The Collaborative International Dictionary of English v.0.48:

Mammalian \Mam*ma"li*an\, a.
   Of or pertaining to the Mammalia or mammals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mammalian
    adj 1: of or relating to the class Mammalia
    n 1: any warm-blooded vertebrate having the skin more or less
         covered with hair; young are born alive except for the
         small subclass of monotremes and nourished with milk [syn:
         mammal, mammalian]