Buck Teeth? Wait a Minute….

New news of a new newsworthy theropod dinosaur in the presses. It’s not published in paper yet, although the journal has it available (free) on its website. Because it’s not published (on paper) I will refrain from discussing the taxon (or the paper) virtually at all.

Needless to say, the phrase “buck tooth” is getting thrown around recently, and it’s not the first time. This phrase generally describes animals with large front teeth (compared to the back teeth), which project out of the mouth or produce a malocclusion. It’s used for humans, rodents of any size (not just unusual), and so forth. It’s useful for Incisivosaurus gauthieri (Xu et al., 2002) which as I showed here (upper left of the first image), has an extremely large first pair of teeth, far larger than any other tooth. These teeth are transversely broad and labiolingually narrow, producing a “chisel-like” shape, just as in humans and rodents.

Epidexipteryx has them, too.

Epidexipteryx hui, based on slab and counterslab of IVPP V15471. Note the huge teeth (Zhang et al., 2008).

Skull of Epidexipteryx hui as preserved, IVPP V15471, slab (b) and counter slab (c), with insets (b and c) showing the relative sizes of the upper and lower teeth.

Or so it seems. Epidexipteryx hui (Zhang et al., 2008) appears to have teeth of a different morphology than Incisivosaurus gauthieri, which appear rounded instead of chisel-shaped. The teeth are also gradually elongated rostrally, rather than abruptly large (like the condition in rodents, or humans, or Incisivosaurus gauthieri). Epidexipteryx hui is also the only “buck-toothed” dinosaur in which the lower teeth are rostrally enlarged just like the uppers, a condition that mirrors Masiakasaurus knopfleri (Sampson et al., 2001), at least as reconstructed by Carrano et al (2011).

Masiakasaurus knopfleri, premaxilla FMNH PR 2453 (left) and as part of the reconstruction of the known material of the skull, where it is rendered as complete (after Carrano et al., 2011).

What is really interesting, though, is that many reconstructions do not take into account the problem of taphonomy is restoring the size of teeth relative to the bones they arise from. This issue causes issues, such as the skull of a juvenile Ceratosaurus (species subjective, there’s a couple named but they may all be subjectively subsumed into Ceratosaurus nasicornis) (Britt et al., 1999). This issue become even more interesting when a recent paper on the potential “venomous” nature of Sinornithosaurus millenii (Gong et al., 2009) was rebutted on the nature of the key dentition being long because they had partially slipped out of their sockets (Gianechini et al., 2010), a case that is almost certainly analogous to the situation in the Ceratosaurus juvenile (although see Gong et al., 2010, who rebut the rebuttal by arguing that other specimens [undescribed] imply the condition in Sinornithosaurus Gianechini et al. used to argue was preservational is prevalent among other specimens). I do not purport to stand in for either sets of authors on this issue, and have no opinion on the situation, which Brian Switek covered here, although it should be noted that in neither case did the authors demonstrate the extent of enamel, and thus the extent of the actual crown of the exposed tooth. This issue is not limited to this particular debate, and lack of language assessing this issue in other taxa for which elongate teeth are argued but for which preservation of the true extent of the crown is unknown, gives me little hope in valuing the relative sizes of teeth as argued.

“Buck teeth” persist in a lot of taxa, it seems, but I think only in a few of them should the term be reasonably applied, and only on the basis of morphology, not preserved extent. Even when the extent of the tooth is great compared to more distal teeth, this seems to be largely gradual rather than abrupt, suggesting two different types of dentition styles resulting in larger rostral-most teeth. The condition of extremely long rostral teeth is present in other theropods, such as a snout referred to Spinosaurus aegyptiacus by dal Sasso et al. (2005), and even may be useful to describe for sauropods, “prosauropod”-grade sauropodomorphans, etc. Is this a useful term to apply to what may be fairly prevalent? I don’t think so. It would be my suggestion that this term is better suited for the tooth shape in connection with the abrupt size different, and especially when that size difference persists along the entire tooth row.

But … more on this later, along with my reconstruction of Masiakasaurus knopfleri‘s unusual skull (I think it was fairly weirder than Carrano et al. give it credit for).

Carrano, M. T., Loewen, M. A. & Sertic, J. J. W. 2011. New materials of Masiakasaurus knopfleri Sampson, Carrano, and Forster, 2001, and implications for the morphology of the Noasauridae (Theropoda: Ceratosauria). Smithsonian Contributions to Paleobiology 95:1-53.
Britt, B. B., Miles, C. A., Cloward, K. C. & Madsen, J. H. 1999. A juvenile Ceratosaurus (Theropoda, Dinosauria) from Bone Cabin Quarry West (Upper Jurassic, Morrison Formation), Wyoming. Journal of Vertebrate Paleontology 19(Supp. to 3):33A.
dal Sasso, C., Maganuco, S., Buffetaut, E. & Mendez, M. A. 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities. Journal of Vertebrate Paleontology 25(4):888–896.
Gianechini, F. A., Agnolín, F. L. & Ezcurra, M. D. 2010. A reassessment of the purported venom delivery system of the bird-like raptor Sinornithosaurus. Paläontologische Zeitschrift 85(1):103-107.
Gong E., Martin, L. D., Burnham, D. A. & Falk, A. R. 2009. The birdlike raptor Sinornithosaurus was venomous. Proceedings of the National Academy of Sciences 107(2):766-768.
Gong E., Martin, L. D., Burnham, D. A. & Falk, A. R. 2010. Evidence for a venomous Sinornithosaurus. Paläontologische Zeitschrift 85(1):109-111.
Sampson, S. D., Carrano, M. T. & Forster, C. A. 2001. A bizarre predatory dinosaur from the Late Cretaceous of Madagascar. Nature 409:504–506.
Xu X., Cheng Y.-n., Wang X.-l. & Chang C.-h. 2002. An unusual oviraptorosaurian dinosaur from China. Nature 419:291-293.
Zhang F.-c., Zhou Z.-h., Xu X., Wang X.-l. & Sullivan, C. 2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 455:1105-1108.