Temporal range: Early Cretaceous, 130 Ma
Hoplitosaurus (meaning "Hoplite lizard") was a genus of armored dinosaur related to Polacanthus. It was named from a partial skeleton found in the ?Barremian-age Lower Cretaceous Lakota Formation of Custer County, South Dakota. It is an obscure genus which has been subject to some misinterpretation of its damaged remains. Although there was a push to synonymize it with Polacanthus in the late 1980s-early 1990s, Hoplitosaurus has been accepted as a valid albeit poorly known genus in more recent reviews.
History and Taxonomy
The holotype specimen, USNM 4752, was discovered in 1898 by Nelson Horatio Darton, near Buffalo Gap Station, and consisted of ribs, caudal vertebrae, part of a right scapulocoracoid, parts of both humeri, a right femur, and a variety of armor (including tall spines). Frederic Augustus Lucas described it briefly in 1901 as a new species of Stegosaurus, but soon gave the material its own genus. Charles W. Gilmore fully described the material in 1914.
William T. Blows and Javier Pereda-Suberbiola both considered the genus to be the same as Polacanthus, creating the new combination Polacanthus marshii, but this has since been rejected. Ken Carpenter and James Kirkland noted that many of the resemblances between the two were more widely distributed among ankylosaurs than previously thought, or were based on damage to the bones, such as some femoral characters.
However, its similarity to Polacanthus has been noted since Lucas first published on it in 1901, the two being most similar in armor, although Hoplitosaurus lacks the sacral shield of armor found in Polacanthus. Today, both are considered to be polacanthine or polacanthid ankylosaurs, depending on classification preference (see for example), or ankylosaurians of uncertain relationships.
One point of similarity that was found to be spurious was the possession of a tail club. In Polacanthus, this turned out to be a misinterpretation of caudal vertebrae, ossified tendons, and armor. (It is not clear what the report in Hoplitosaurus was based on).
Blows (2001) reconsidered the armor in light of new data on polacanthine dinosaurs, and found it to fall into the following categories:
- Pectoral spines
- Presacral spines
- Splates (spine+plate) from the sacral region
- Tall, asymmetric, hollow-based caudal plates
- Small to large solid-based, ridged ossicles (filling spaces)
- Lucas, F.A. (1901). A new dinosaur, Stegosaurus marshi, from the Lower Cretaceous of South Dakota. Proceedings of the United States National Museum 23(1224):591-592.
- Gilmore, C.W. (1914). Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus Stegosaurus. United States National Museum Bulletin 89:1-136.
- Lucas, F.A. (1902). Paleontological notes. The generic name Omosaurus. A new generic name for Stegosaurus marshi. Science, new series 16(402):435.
- Blows, W.T. (1987). The armoured dinosaur Polacanthus foxi from the Lower Cretaceous of the Isle of Wight. Palaeontology 30(3):557-580.
- Pereda-Suberbiola, J. (1991). Nouvelle évidence d'une connexion terrestre entre Europe et Amérique du Nord au Crétacé inférior: Hoplitosaurus synonyme de Polacanthus (Ornithischia: Ankylosauria). C.R. Academie Science, Paris 313:971-976. [French]
- Pereda-Suberbiola, J. (1994). Polacanthus (Ornithischia, Ankylosauria), a transatlantic armoured dinosaur from the Early Cretaceous of Europe and North America. Palaeontographica Abteilung A 232(4-6):133-159.
- Carpenter, K., and Kirkland, J.I. (1998). Review of Lower and middle Cretaceous ankylosaurs from North America. In: Lucas, S.G., Kirkland, J.I., and Estep, J.W. (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin 14:249-270.
- Carpenter, K. (2001). Phylogenetic analysis of the Ankylosauria. In: Carpenter, K. (ed.). The Armored Dinosaurs. Indiana University Press:Bloomington, 455-483. ISBN 0-253-33964-2
- Vickaryous, M.K., Maryańska, T., and Weishampel, D.B. (2004). Ankylosauria. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (second edition). University of California Press:Berkeley, 363-392. ISBN 0-520-24209-2
- Blows, W.T. (2001). Dermal armor of the polacanthine dinosaurs. In: Carpenter, K. (ed.). The Armored Dinosaurs. Indiana University Press:Bloomington, 363-385. ISBN 0-253-33964-2