| apatosaurus (ə-pāt'ə-sôr'əs) or apatosaur (ə-pāt'ə-sôr'əs) A very large sauropod dinosaur of the genus Apatosaurus (or Brontosaurus) of the late Jurassic Period. Apatosaurs had a long neck and tail and a relatively small head. See Note at brontosaurus. |