Haplocanthosaurus

Taxobox
name = "Haplocanthosaurus"
fossil_range = Late Jurassic

---

image_width = 250px
image_caption = "Haplocanthosaurus priscus" sacrum.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Sauropodomorpha
infraordo = Sauropoda
familia = Haplocanthosauridae
familia_authority = Bonaparte, 1999
genus = "Haplocanthosaurus"
genus_authority = Hatcher, 1903
subdivision_ranks = Species
subdivision =
* "H. priscus" (Hatcher, 1903) (type)
* "H. delfsi" Hatcher, 1903

"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. It was first 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.]

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=clade
label1=Macronaria
1=clade
1="Haplocanthosaurus"?
2=Camarasauromorpha
label2=Diplodocoidea
2=clade
1="Haplocanthosaurus"?
label2=Diplodocomorpha
2=clade
1=Rebbachisauridae
label2=Flagellicaudata
2=clade
1=Dicraeosauridae
2=Diplodocidae

Description

"Haplocanthosaurus" was one of the smallest sauropods of the Morrison. While most 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 meters (46 feet) and an estimated weight of 14.5 metric tons.McIntosh, J.S., Brett-Surman, M.K., and Farlow, J.O. (1997). "Sauropods." Pp. 264 –290 in Farlow, J.O. and Brett-Surman, M.K. (eds.), "The Complete Dinosaur". Indianapolis: Indiana University Press.]

Specimens

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.

References

-The Cleveland Museum of Natural History