Haplocanthosaurus

Haplocanthosaurus (meaning "simple spined lizard") is a genus of diplodocoid sauropod dinosaur. Two species, H. delfsi and H. priscus, are known from incomplete fossil skeletons. They lived during the Late Jurassic (Kimmeridgian stage), 155 to 152 million years ago in North America. The type species is H. priscus, named in 1903 John Bell Hatcher , and the referred species H. delfsi was discovered by a young college student named Edwin Delfs in Colorado, United States and described by Jack McIntosh and Michael Williams in 1988. Haplocanthosaurus specimens have been found in the lowermost layer of the Morrison Formation, along with Hesperosaurus mjosi, Brontosaurus yahnahpin, and Allosaurus jimmadseni.

==Discovery== thumb|left|Quarry map showing holotype of H. priscus There are four known specimens of Haplocanthosaurus: one of H. delfsi, and three of H. priscus. Of these, the type of H. delfsi is the only one complete enough to mount. The mounted specimen of H. delfsi now stands in the Cleveland Museum of Natural History, albeit with a completely speculative replica skull, as the actual skull was not recovered. Present in stratigraphic zones 1, 2, and 4. Recently described specimens from a different region of the Morrison Formation were assigned to Haplocanthosaurus in 2014. The study describing them noted that Haplocanthosaurus is known for certain from at least four specimens, assigned to H. priscus (CM 572), H. utterbacki (=H. priscus; CM 879), H. delfsi (CMNH 10380), and H. sp. (MWC 8028). Up to seven additional specimens have been assigned to Haplocanthosaurus? or Haplocanthosauridae indet. One potential specimen has been nicknamed "Big Monty," for its discovery in Montana. It has been claimed to measure an incredible long. However, much controversy surrounds the specimen and, as such, little is truly known about it.