Work by Dodson ( 1975 ) recognized that there was many less taxa present in Alberta . Tetragonosaurus was found to be juveniles of Corythosaurus or Lambeosaurus . T. erectofrons was assigned to Corythosaurus based largely on biometric information . The only non @-@ typic specimen of Tetragonosaurus , assigned to T. erectofrons , was found later to be referable to Hypacrosaurus , although the holotype of the species was still found to be assignable to Corythosaurus .