When playing around with the idea that how we orient our material when we measure it, it struck me how alien the images look when you reposition them. We are actually unaccustomed to thinking of bones in certain ways when we see them in isolation. In the past, objects being viewed would be rendered in sterile positions, stripped of all associational relationship, in order to preserve the sense of separation of environment from object we try to train ourselves to. But this has the unfortunate effect of preventing us from seeing many objects in context. In order to see the tree, we had to remove the forest; but to see the forest, conversely, we have to ignore the tree. In other words, when we change perspective, we have to change this impression of environmental sterilization of our subjects.
As an example, I have posted occasionally on my desire to examine the effects of ONP on vertebral series: Not because it’s somehow reflective of their natural posture in any way, but as a way to “sterilize” the vertebrae from external influences. Typically, we arrange our vertebrae when the ventral margins of the centrum entirely horizontal, and everything is measured from there. Or, say, we oriented it so that the posterior centrum articulation is oriented vertical, and so on. I discussed this here, when talking about Naish & Sweetman (2011)’s tiny theropod, based on a single vertebra. Different views of the vertebra do not actually line up, making it clear that the information across each view is not preserving corresponding available information. I should, for instance, be able to take the same direct measurement of the anterior centrum height regardless of side or cranial view, but the actual orientation of the photo may interfere with this. Or, because the plane of the photograph was not quite in line with a previous one, an object from the right side when viewed anteriorly will not be visible when viewed posteriorly, when it should. I will get to this in some time, as I have some ideas on the matter.
I have talked about what it means to orient your vertebrae. Scott Hartman is discussing this topic in a different way by asking the question about how schematic our skeletal reconstructions should be? How realistic, rather, or how close must the depiction of our bone drawings and their arrangement be to properly depict or convey your information? In a way, this is a response to this question in my own, convoluted, obscure, obdurate and obfuscatory way.
I did an experiment:
Here, I have depicted the entire preserved vertebral series of IVPP V10600, holotype of Sinraptor dongi (Currie & Zhao, 1994). I have arranged them in three ways, which all depend on selecting a “baseline.” With the exception of conjoined vertebrae, all vertebrae were individually positioned relative to one another. Also, cervical vertebra six (CV6) is shown only in the last series, as the centrum of this vertebra is incomplete. In the first row of vertebrae, the posterior face of the centrum is arranged so that the dorsal edge near the neural arch is positioned vertically with the ventral edge, excluding the slight cranial curve of the “lip.” This causes the posterior face’s concave or convex margin (not the face itself) to show how far it extends from the vertical axis, but also allows the viewer to see how “high” or “low” the anterior face of the centrum is.
In the second row of vertebrae, I have made the ventral edges of the centrum (the base of the posterior margin of the face, and the base of the anterior margin of the face, excluding any hypapophyses present, as are present in DV1 and DV2). This shows you how “anterior” the vertebra is oriented, how strongly the neural arch is skewed either cranially or caudally. Note that only the cranialmost vertebrae are positioned differently, owing to the strong anterodorsal slant of the posterior centrum facet. Only DV2 did not need to be re-oriented between these two depictions, due to a very “square” centrum: the ventral and caudal axes in this case are a perfectly perpendicular 90°.
The third is the so-called ONP (osteological neutral pose), oriented so that the anterior and posterior facets of the centrum are as close to parallel along their lengths and where the anterior tip of the prezygapophyses of one vertebrae perfectly align to the anterior end of the postzygapophyses of the preceding vertebra. This produces an arch in the dorsal vertebra, and a coinciding arch in the cervical vertebra, connected by a “valley” in the transitional series. No S-curve is preserved. I should not that, even including CV6, I am estimating the positional relationships of the intervening vertebrae by “copying” the vertebrae on each side of the gap and adding them into the middle. There is considerable potential error here due to not separating CVs 3, 4 and 5 and CVs 9 and 10 from one another; certainly, CV9 is oriented more strongly dorsally based on this baseline than I would reconstruct, although CVs 3, 4 and 5 are not and would be oriented more strongly ventrally. In short, the neck would preserve a lopsided J-shape.
We are not used to looking at vertebrae in this manner, trying to realign them to compete for what is useful about their alignment, and I am only scratching the surface of what this can show us. For example, degree of slant of vertebrae can increase and decrease, relative proportions can change and sometimes very strongly, although potentially not by much due to the quantum of individual variation, whatever it might be.
This becomes even more exaggerated when we deal with skulls, as I intimated before:
If you are even slightly used to looking at sauropod or oviraptorid skulls, this might come as something of a shocker. If I really wanted to, the sauropod version of this would show Nigersaurus tacqueti because I’m really mean like that. But this elaborates on my earlier argument about basal alignment of skulls. Typical skull length is measured from the anterior end of the premaxilla to the posterior end of the distal end of the quadrate. If I used this measure and made it horizontal, then this skull would be about 22 cm long. However, if I were to place the skull so that the basal endocranial floor were horizontal, and which corresponds to the alignment of the jugal, and measured the horizontal from that, I would arrive at a length of about 20.6 cm, a shrinkage of nearly 6%! Moreover, height:length ratios change, the relative position of muscle origins and insertions change, and the perspective of the skull in “anterior” and “dorsal” are very, very different from what is expected.
When we orient our elements, we need to do so with some mind to why. When we measure them, however, me need to do so with knowing that the orientation, axes, and alignment are useful. Moreover, we need to show that when three or four different authors produce different measurements from ostensibly the same source, that they are measuring from the same equivalent points as one another. This is a lot harder when working with digital images, because you cannot correct the orientation to measure. This does not mean we have to lose the idea of depicting elements in the “traditional” manner, but that when we do so, we state clearly why; for some, it may simply be a need to show a perspective in which the element of choice is more clearly visible, whereas it is normally obscured in the “standard” plane of view. I refer to this as “aspect,” the shape or orientation of the object in the “view,” and it is clear in the above two images. The vertebrae form a weak, double-peak oscillation (aspect) in lateral view (view frame), while the skull of Citipati osmolskae above forms a triangle in aspect when viewed in the horizontal frame (view).
This is overly specific language, and is technical, but maybe it should be, when we get around to discussing how our efforts should be reproduced. Otherwise, we make the task just that much harder for other people who have to constantly remeasure, recode, revise earlier work, instead of using what that earlier work is supposed to be: reference material. When people talk about trying to unnecessarily repeat earlier work, they ignore that they must do so constantly because it is impossible to avoid it when there exist few standards of element examination and perspective framing, and those that do often compete with one another. I’ll leave you with this, from XKCD, which came literally as I was producing the second image above there:
Clark, J. M., Norell, M. A. & Barsbold R. 2001. Two new oviraptorids (Theropoda: Oviraptorosauria), upper Cretaceous Djadokhta Formation, Ukhaa Tolgod, Mongolia. Journal of Vertebrate Paleontology 21(2):209-213.
Currie, P. J. & Zhao X.-j. 1994. A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People’s Republic of China. Canadian Journal of Earth Sciences — Revue canadienne de sciences de la Terre 30:2037-2081. [Printed 1993, but released in 1994.]
Naish, D. & Sweetman, S. C. 2011. A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: Evidence from a new vertebrate-bearing locality in south-east England. Cretaceous Research 32(4):464-471.