In Depth
Haplocanthosaurus was a genus of sauropod dinosaur that lived in North America during the late Jurassic period. The name Haplocanthosaurus was actually the second choice of name for this dinosaur as the palaeontologist who first described it, John Bell Hatcher, originally chose the name Haplocanthus. However, after this Hatcher became aware of a fish genus which sounded just like this, and so in the belief that the name was preoccupied. Hatcher renamed Haplocanthus Haplocanthosaurus.
While Hatcher’s actions to be scientifically accurate are commendable, he was actually right the first time. While the fish genus sounded similar, it was actually spelt with an ‘a’ as Haplacanthus, while the original spelling of Haplocanthus was spelt with an ‘o’ after the ‘l’. Although a subtle difference, it was still enough of a difference to define Haplocanthus and Haplacanthus as separate genera. Surprisingly this was not actually noticed till many years afterwards, and by that time the name Haplocanthosaurus was in familiar use. For this reason a petition was sent to the ICZN, the body that watches over the naming of animals, to grant Haplocanthosaurus ‘protected name’ status since Haplocanthus had not been used since the initial change. This was accepted so even though Haplocanthus had technical priority as the name, Haplocanthosaurus is the one used to refer to the genus for greater clarity. The granting of protected names is not a common occurrence, though one of the most famous dinosaurs of all time, Tyrannosaurus, also has protected name status after it was realised that fossils of the genus were named as something else before Tyrannosaurus was established (details are on the main Tyrannosaurus page).
So far fossils of a few Haplocanthosaurus have been found, though as is often the case, the skull of this sauropod is still unknown. So far only elements of the post cranial skeleton such as a sacrum and vertebrae have been found. Though incomplete, Haplocanthosaurus has been estimated to reach lengths just short of fifteen meters, which means that Haplocanthosaurus were actually quite small when compared to many other late Jurassic era sauropods.
Exactly what kind of sauropod the Haplocanthosaurus genus was is actually still a matter of debate. The main two options are that the genus represents either a form of diplodocid (very long and thin build) or a macronarian (taller, shorter and more stocky), though whichever one Haplocanthosaurus would have been a primitive form. There are good arguements for both, though more current research learns slightly more towards Haplocanthosaurus being a diplodocid. Really though we need to discover more fossils of Haplocanthosaurus, ideally (and hopefully) a skull since macronarians and diplodocids had very different skulls to one another.
As already mentioned, Haplocanthosaurus would have been a primitive form of either of these groups, indeed, the genus name Haplocanthosaurus translates to English as ‘simple spined lizard’ in reference to the primitive and unspecialised form of the vertebrae. It seems strange that such a primitive form of sauropod should be living in a time and place which also saw the presence of advanced diplodocids and macronarians. It may be that Haplocanthosaurus was actually a form of sauropod that was more common earlier on in the Jurassic, and that the Haplocanthosaurus genus was actually a late surviving form of the more primitive ancestors of the more advanced late Jurassic sauropods of the Morrison Formation.
Haplocanthosaurus is so far only known from the Morrison Formation of the United States, a large Formation that also yielded the discovery of other diplodocid sauropods such as Barosaurus, Apatosaurus and even the type genus of the group, Diplodocus. Other sauropods such as macronarians like Camarasaurus and Brachiosaurus are also present. The main predators of the Morrison Formation were large theropod dinosaurs such as Allosaurus, Torvosaurus and Saurophaganax, and given the overall smaller size of Haplocanthosaurus, it’s conceivable that these predators, and others like them may have occasionally targeted this sauropod as prey.
Haplocanthosaurus should not be confused with the predatory theropod Acrocanthosaurus, a very different kind of dinosaur that lived in North America during the early Cretaceous.
Further Reading
- A new name for the dinosaur Haplocanthus Hatcher - J. B. Hatcher - 1903a. - Early evolution and higherlevel phylogeny of sauropod dinosaurs. - J. A. Wilson & P. C. Sereno - 1998. - The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda). - M. P. Taylor & D. Naish - 2005. - A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). J. A. Whitlock - 2011. – Haplocanthosaurus (Saurischia: Sauropoda) from the lower Morrison Formation (Upper Jurassic) near Snowmass, Colorado. – Volumina Jurassica. 12 (2): 197–210. – J. R. Forster & M. J. Wedel – 2014.
