The Collaborative International Dictionary of English v.0.48:

Reptilian \Rep*til"i*an\ (-an), a.
   Belonging to the reptiles.
   [1913 Webster]

   Reptilian age (Geol.), that part of geological time
      comprising the Triassic, Jurassic, and Cretaceous periods,
      and distinguished as that era in which the class of
      reptiles attained its highest expansion; -- called also
      the Secondary or Mezozoic age.
      [1913 Webster]