The Collaborative International Dictionary of English v.0.48:

Coetaneous \Co`e*ta"ne*ous\, a. [L. coaetaneus; co- + aetas
   age.]
   Of the same age; beginning to exist at the same time;
   contemporaneous. -- Co`e*ta"ne*ous*ly, adv.
   [1913 Webster]

         And all [members of the body] are coetaneous.
                                                  --Bentley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

coetaneous
    adj 1: of the same period [syn: coetaneous, coeval,
           contemporaneous]