Osteological Neutral Pose – WP#16

“Osteological Neutral Pose,” or ONP, was first introduced into the literature by Stevens and Parrish [1] in utilizing a method to attempt a “neutral,” or unbiased, attempt at articulating skeletons from which to then manipulate for range of motion studies. Applied initially to sauropods, it projected that virtually all sauropods had a neutral neck posture that was nearly horizontal, even those with the longest necks, or deflected or curved below the horizontal [2,3]. This idea came under scrutiny from various workers, although formal publication of criticism would not arrive until much later [4,5].

Regardless of its utility, ONP describes in the cervical and dorsal column, as well as the caudals to a degree [n1] the static position between centra and zygapophyses (and in some taxa, accessory articulations). While contradictory conclusions such as in Taylor et al. [5] are based on radiographic study of living animals, and that of Paul [4] is based on inferred reasoning of ecology (that diet preference for long necks is always for vertical reach, and long horizontal necks make the animal “vulnerable”), ONP has a close fit to biological orientation of the neck [3], suggesting that Stevens and Parrish [1,3] are not, in fact confusing themselves. The contradiction of Taylor et al. [5] was previously suggested (here) to have some problematic definitional useage (e.g., “active pose” being undefined, and non-instructional to habitus: Are we to suggest that upright, alert posture is the constraint to which osteological articulation should conform itself? If so, why?). Recent work [6,7] has suggested that sauropod necks are not characteristically held at an implied angle, but nor were they explicitly capable of achieving a high, moderate angle, contra Paul [4] or Taylor et al. [5] or Stevens and Parrish [1,2,3].

ONP in the vertebrae of sauropods is one thing, but here I will take a temporary departure to illustrate ONP in a theropod skeleton, something rarely done. In this case, I intent to show what ONP looks like (not to argue that it is indicative of the true living posture of the neck in any position (although it is likely to come up once in a while) in Majungasaurus crenatissimus.

Majungasaurus crenatissimus, nearly complete cervical, dorsal, sacral, and anterior caudal vertebral series in ONP. After O'Connor (2007) (see ref. 8).

Ventriflexion in the dorsal series is nothing new, and various authors have argued this to various sauropods, ornithischians and theropods, although it does not tend to be universal. Ventriflexion in the cervical series, however, belies the typical argument that the series is S-shape when articulated, which it is clearly not (or at least, the reflex at the caudal end of the cervical series is present, but so minor as to blend with the dorsal series imperceptibly). The functional implications of this, if this pose reflects anything natural, would require detailed analysis, as it contradicts the typical arguments for head elevation, retraction of the center of gravity, “active posture” of [5], etc. (although it is, in turn, contradicted by them). To attain a high, S-shaped or swan-like posture, moderate to extreme dorsiflexion only of the base of the neck would be required.

It should be noted in the above that the basis for articulation was complete overlap and alignment of the zygapophyses in all vertebrae; the articulation at the centra was secondary, and occasionally ignored (especially in the cervical series). Completing the gaps in the cervical series would result in more ventroflexion of the series, rather than less, and make the neck more or less C-shaped. An interesting consequence of this articulation is that all neural spines are parallel to one another, and while this is certainly interesting and unlikely, it was an artifact of the zygapophyseal (and non central) alignment. The caudal series appears to belong to this specimen, despite its apparent larger size (the centra are much longer, but the same relevant height as the posterior sacrals, and thus, imply they belong to the same sized animal [8]).

[1] Stevens, K. A. & Parrish, J. M. 1999. Neck posture and feeding habits of two Jurassic sauropod dinosaurs. Science 284:798-800.
[2] Stevens, K. A. & Parrish, J. M. 2005. Neck posture, dentition, and feeding strategies in Jurassic sauropod dinosaurs. p212-232 in Carpenter & Tidwell (eds.) Thunder Lizards: The Sauropodomorph Dinosaurs. (University of Indiana Press, Bloomington.)
[3] Stevens, K. A. & Parrish, J. M. 2005. Digital reconstructions of sauropod dinosaurs and implications for feeding. p178-200 in Wilson & Curry-Rogers (eds.) The Sauropods: Evolution and Paleobiology. (University of California Press, Berkeley.)
[4] Paul, G. S. 2000. Restoring the life Appearance of dinosaurs. p78-106 in Paul (ed.) The Scientific American Book of Dinosaurs. (Byron Press/Scientific American, New York City.)
[5] Taylor, M. P., Wedel, M. J. & Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54:213-220.
[6] Christian, A. & Dzemski, G. 2007. Reconstruction of the cervical skeleton posture of Brachiosaurus brancai Janensch, 1914 by an analysis of the intervertebral stress along the neck and a comparison with the results of different approaches. Fossil Record 10:37-48.
[7] Christian, A. 2010. Some sauropods raised their necks — evidence for high browsing in Euhelopus zdanskyi. Biology Letters 10:37-48.
[8] O’Connor, P. M. 2007. The postcranial axial skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. in Sampson & Krause (eds.) Majungasaurus crenatissimus (Theropoda: Abelisauridae from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir 8. Journal of Vertebrate Paleontology (supp. to 2):127-162.

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One Response to Osteological Neutral Pose – WP#16

  1. Pingback: Wrench in the Works of Head Attitude | The Bite Stuff

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