Haplocanthosaurus (meaning "simple spined lizard") is a
genus of
sauropod dinosaur. Two species,
H. delfsi and
H. priscus, are known from incomplete
fossil skeletons. It lived during the late
Jurassic period (
Kimmeridgian -
Tithonian stages), 144 to 156 million years ago. The type species is
H. priscus, and the referred species
H. delfsi was discovered by a young college student named Edwin Delfs in
Colorado.
Haplocanthosaurus specimens have been found in the very lowest layer of the
Morrison Formation, along with
Hesperosaurus,
Eobrontosaurus, and
Allosaurus jimmadensi.
[Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. 389pp.] Description
Haplocanthosaurus was one of the smallest sauropods of the Morrison.
While some Morrison sauropods could reach lengths of over 20 meters (or over 70 feet),
Haplocanthosaurus wasn't nearly as large, and reached a total length of 14.8 meters (49 feet) and an estimated weight of 12.8 metric tons.
[Mazzetta, G.V., Christiansen, P. and Fariña, R.A. (2004). "Giants and Bizarres: Body size of some southern South American Cretaceous dinosaurs." Historical Biology, 16(2): 71-83.] Specimens
Haplocanthosaurus priscus sacrum
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 adult, and 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 dragging tail posture and a completely speculative replica skull, as the actual skull was not recovered. Present in stratigraphic zones 1, 2, and 4.
[Foster, J. (2007). "Appendix." Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327-329.] Classification
Haplocanthosaurus priscus was originally named
Haplocanthus priscus by
John Bell Hatcher in 1903. Soon after his original description, Hatcher came to believe the name
Haplocanthus had already been used for a genus of
acanthodian fish (
Haplacanthus, named by
Louis Agassiz in 1845), and was thus preoccupied. Hatcher re-classified his sauropod later in 1903, giving it the new name
Haplocanthosaurus.
[Hatcher, J.B. (1903a). "A new name for the dinosaur Haplocanthus Hatcher." Proceedings of the Biological Society of Washington, 16: 100.] However, the name was not technically preoccupied at all, since there was a variation in spelling: the fish was named
Haplacanthus, not
Haplocanthus. While
Haplocanthus technically remained the valid name for this dinosaur, Hatcher's mistake was not noticed until many years after the name
Haplocanthosaurus had become fixed in scientific literature. When the mistake was finally discovered, a petition was sent to the
ICZN (the body which governs scientific names in zoology), which officially discarded the name
Halplocanthus and declared
Haplocanthosaurus the official name (ICZN Opinion #1633).
Originally described as a "
cetiosaurid",
José Bonaparte decided in 1999 that
Haplocanthosaurus differed enough from other sauropods to warrant its own
family, the
Haplocanthosauridae.
[Bonaparte, J. F. (1999). "An armoured sauropod from the Aptian of northern Patagonia, Argentina." In Tomida, Y., Rich, T. H. & Vickers-Rich, P. (eds.), 1999. Proceedings of the Second Gondwanan Dinosaur Symposium, National Science Museum Monographs #15, Tokyo: 1-12.]Phylogenetic studies have failed to clarify the exact relationships of
Haplocanthosaurus with any certainty. Studies have variously found it to be more primitive than the
neosauropods,
[Upchurch, P. (1999). "The phylogenetic relationships of the Nemegtosauridae (Saurischia, Sauropoda)." Journal of Vertebrate Paleontology, 19: 106–125.] a primitive
macronarian (related to the ancestor of more advanced forms such as
Camarasaurus and the
brachiosaurids),
[Wilson, J.A., and Sereno, P.C. (1998). "Early evolution and higherlevel phylogeny of sauropod dinosaurs." Society of Vertebrate Paleontology Memoir, 5: 1–68.] or a very primitive
diplodocoid, more closely related to
Diplodocus than to
titanosaurs, but more primitive than
rebachisaurids.
[Wilson, J.A. (2002). "Sauropod dinosaur phylogeny: critique and cladistic analysis." Zoological Journal of the Linnean Society, 136: 217–276.]In 2005,
Darren Naish and
Mike Taylor reviewed the various proposed positions of
Haplocanthosaurus in their study of diplodocoid phylogeny.
[Taylor, M.P. and Naish, D. (2005). "The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda)." PaleoBios, 25(2): 1–7.] These positions are represented in the
cladogram below.
{{clade| style=font-size:100%;line-height:80%
|label1=
Sauropoda|1={{clade
|1=
Haplocanthosaurus?
|label2=
Neosauropoda |2=
}}
}}
