Because of the incomplete understanding of hadrosaurids at the time, following Marsh's death in 1897 Claosaurus annectens was variously classified as a species of Claosaurus, Thespesius or Trachodon.
Zbog nepotpunog razumijevanja hadrosaurida u to vrijeme, nakon Marshove smrti 1897. godine, Claosaurus annectens se svrstavao kao vrsta rodova Claosaurus, Thespesius ili Trachodon.