The Collaborative International Dictionary of English v.0.48:

Reptilian \Rep*til"i*an\, n. (Zool.)
   One of the Reptilia; a reptile.
   [1913 Webster]

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]

WordNet (r) 3.0 (2006):

reptilian
    adj 1: of or relating to the class Reptilia
    n 1: any cold-blooded vertebrate of the class Reptilia including
         tortoises, turtles, snakes, lizards, alligators,
         crocodiles, and extinct forms [syn: reptile, reptilian]