Aublysodon

Eumetazoa

Aublysodon Temporal range: Late Cretaceous, 83–65.5 Ma PreЄ Є O S D C P T J K Pg N
Illustrations of the teeth by Leidy and O. C. Marsh, 4: A. mirandus 5: A. amplus 6: A. cristatus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Superfamily:	†Tyrannosauroidea
Family:	†Tyrannosauridae
Subfamily:	†Aublysodontinae Nopcsa, 1928
Genus:	†Aublysodon Leidy, 1868
Type species
†Aublysodon mirandus Leidy, 1868
Species
†A. mirandus Leidy, 1868 †A. lateralis? Cope, 1876 †A. grandis? (Marsh, 1890 [originally Ornithomimus]) †A. amplus? Marsh, 1892 †A. cristatus? Marsh, 1892

Aublysodon (uncertain derivation; perhaps "backwards-flowing tooth"?) is a name given to a large number of carnivorous dinosaur teeth of a certain form found in numerous late Cretaceous period geological formations. The genus was named by Joseph Leidy in 1868, though it is now considered dubious, because the type specimen consists only of an isolated premaxillary tooth, found in the Judith River Group of Montana. Although this specimen is now lost, similar teeth have been found in many US states, western Canada, and Asia.^[1] These teeth almost certainly belong to juvenile tyrannosaurine tyrannosaurids, but most have not been identified to species level. However, it is likely that the type tooth (and therefore the name Aublysodon mirandus itself) belongs to one of the species in the genus Daspletosaurus, which was present in contemporary formations, and which matches specific details of the original tooth.^[2] The synapomorphies alleged to distinguish the Aublysodontinae, especially lack of serrations on premaxillary teeth could have been caused by tooth wear in life, postmortem abrasion, or digestion.^[3] Most other "Aublysodontine"-type teeth may be from ontogenetic stages or sexual morphs of other tyrannosaurids.^[3]

History

In the mid-to-late 19th century many dinosaur taxa were named for isolated teeth; such genera include Trachodon, Palaeoscincus, and Troodon. Even before the badlands of North America started revealing the bones of Tyrannosaurus, teeth turning up in many localities in the Western United States revealed the presence of large predatory dinosaurs.

Leidy named nonserrated premaxillary teeth Aublysodon in 1868. These specimens had been collected from the Judith River Badlands of Montana.^[1] This tooth-based taxon was a mystery for a long time since no further skeletal elements were found that could be assigned with certainty to the teeth. Similar teeth are found in specimens of juvenile Daspletosaurus, and it is likely that teeth referred to Aublysodon came from that genus.^[2]

The first skeletal material referred to Aublysodon was a partial skull unearthed in Montana^[1] in the 1980s. The skull bore pointed teeth attached to a long narrow skull the length of an average human arm. First thought to be a juvenile Tyrannosaurus, then interpreted as a large dromaeosaurid, this "Jordan theropod" was given the name Aublysodon molnari by Paul in 1988. It was re-classified in the distinct genus Stygivenator by Olshevsky in 1995, but was later (2004) reinterpreted to be a juvenile Tyrannosaurus rex by Thomas Carr and Tom Williamson. Two contemporary species based solely on teeth, Aublysodon amplus and A. cristaus, may also represent teeth from juvenile T. rex.^[4]

Another partial skeleton from New Mexico was considered to represent Aublysodon, but later research by Thomas Carr and Tom Williamson (2004) has shown that it is probably referable to Daspletosaurus.^[4]

Now that the type specimen of Aublysodon is missing, and coupled with the presence of Aublysodon teeth in juvenile tyrannosaurines, the name is no longer considered to represent a real biological taxon.^[4]

Classification

Aublysodon was once thought to belong to a unique subfamily of tyrannosaurids called the Aublysodontinae. Holtz proposed a definition of the Aublysodontinae in 2001, "Aublysodon and all taxa sharing a more recent common ancestor with it than with Tyrannosaurus."^[5]

Holtz proposed a definition of the Tyrannosauridae in 2001 as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon", using Aublysodon as an anchor taxon.^[5] Paul Sereno has also used Aublysodon as an anchor taxon for the tyrannosauridae, although his definition was problematic for other reasons.^[3]

Footnotes

1. ^ ^{a b c} "Aublysodon." Dodson, et al. Page 128.
2. ^ ^{a b} Currie, P. (2005). "Theropods, including birds." Pp. 367-397 in Currie and Koppelhus (eds)., Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Bloomington: Indiana University Press.
3. ^ ^{a b c} "Results," in Holtz (2001). Pg. 67.
4. ^ ^{a b c} Carr and Williamson (2004).
5. ^ ^{a b} "Results," in Holtz (2001). Pg. 66.

References

• Carr, T.D.; and Williamson, T.E. (2004). "Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America". Zoological Journal of the Linnean Society 142 (4): 479–523. doi:10.1111/j.1096-3642.2004.00130.x. 
• Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 128. ISBN 0-7853-0443-6.
• Holtz, TR, Jr. (2001), The phylogeny and taxonomy of the Tyrannosauridae in K Carpenter & D Tanke [eds.], Mesozoic Vertebrate Life. Indiana Univ. Press, pp. 64-83.
• Jacobsen, A.R. 2001. Tooth-marked small theropod bone: An extremely rare trace. p. 58-63. In: Mesozioc Vertebrate Life. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.

External links

Dinosaurs portal

• Aublysodon in The Dinosaur Encyclopaedia