Non-hyperbolic ergodic measures for non-hyperbolic homoclinic classes
  We prove that for a generic $C^1$-diffeomorphism existence of a homoclinic class with periodic saddles of different indices (dimension of the unstable bundle) implies existence an invariant ergodic non-hyperbolic (one of the Lyapunov exponents is equal to zero) measure of $f$. 
Lorenzo J. Diaz, Anton Gorodetski