Apatosaurus

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Apatosaurus mother and daughter. The daughter made a physical 60' long appearance along with a virtual appearance on the screen of a live, interactive version of DinoMorph™ at the "Dinosaurs: Ancient Fossils, New Discoveries" exhibition that opened at the American Museum of Natural History in May, 2005 and subsequently traveled to other venues.

The Carnegie Museum of Natural History Apatosaurus louisae specimen number 3018 was modeled in detail within DinoMorph™ on the basis of dimensional data in Gilmore's original monograph (and personal measurements of the specimen to model the zygapophyseal facets in the neck. Later, Phil Platt very graciously provided me dimensional engineering drawings of the entire skeleton, from which I refined the model. Phil, through years of exquisite modeling and much investigative work, created a 1/12 scale model of this sauropods, and in the process, resolved a number of errors in previous reconstructions (including some physical restorations in the original mount). Through physical posing of his model and a convergent set of discussions with fellow sauropod forelimb worker Matt Bonnan, Phil proposed a very informed interpretation of its forelimb posture.

As discussed elsewhere, the neutral position of a given neck can be reconstructed from lateral view illustrations of the individual vertebrae, provided they are geometrically accurate and all of the same scale (which has to be corrected when working from many of the original monographs). The accuracy of the reconstruction is ultimately dependent on the condition of the original material, and fortunately most of Apatosaurus louisae CM 3018 is sufficiently undistorted as to permit a good approximation to the original neutral pose. Below is a view of nearly the entire presacral vertebral column of A. louisae based on Gilmore's monograph, and directly below is a lateral view of the simplified, but dimensionally-accurate DinoMorph™ model. (Click on any image to see a larger version.)

Note that the vertebrae of the dorsal vertebral column (the sauropod's back) forms a very shallow arch. Phil Platt independently concluded the arch to the dorsal vertebral column was quite shallow. Note that the osteology suggests a much straighter trunk than one finds in may artistic reconstructions, such as the following detail by Greg Paul:

If one were to adopt this high arch condition, like this:

that curvature would have caused the base of the neck to slope downward significantly:

and (for this restoration of the undeflected neck) that high arch would bring the head right down to ground level. But such substantial curve to the back, particularly the downturn in the anterior dorsals, is greater than that suggested by the actual osteology. For instance, here are the dorsals of Apatosaurus excelsus, which, when restored into approximate neutral position, forms a much shallower curve (essentially the same as in A. louise, above):

Some other sauropods appear to have dorsal vertebral columns of similarly low arch. For instance, the sister taxon Diplodocus carnegii is sufficiently well preserved and complete to permit a neutral pose reconstruction of its dorsal vertebral column based on illustrations from Hatcher's original description. Here is the column from the C10 to D10, covering the cervicodorsal and dorsal vertebral columns (please visit the DinoMorph™ reconstruction of Diplodocus for further information):

So, back to Apatosaurus, the osteological evidence suggests that the back was not as arched as often depicted artistically. This sauropod more likely had a low arch as below:

which has this effect on head height (neck curvature being held constant):

The following shows the overall DinoMorph™ model in the same left lateral view, with a slightly more ventral position for the pectoral girdles:

Here are some details of the trunk:

And here is some movies showing the range of motion of the neck of Apatosaurus louisae, based on limits estimated in (Stevens & Parrish, 1999). It has been observed that our analysis does not incorporate the increase in overall feeding envelope provided by anterior trunk movements, and we agree. Our intention is to simply compare neck flexibility however, not to measure the additional stretch provided by movement in the shoulder (which is variably constrained by the pectoral musculature across modern taxa, and therefore very difficult to estimate for sauropods) and the lateral shift possible by taking a few side steps with the forelimbs (pivoting about a point between the hind limbs to reach that tasty morsel just about out of reach). To try to incorporate the whole body, where then to stop? Should we allow leaning and twisting anteriorly but no sidesteps? Or allow one side step? All that sounds too arbitrary, so we are just looking at the flexibility of the neck in isolation.

dunking under water during ventriflexion, useful in lacustrine feeding [.mov 140 KB] [.mov 7 MB]
same exploration of the range of motion, but with dorsal 'nuchal' ligaments supporting neck [.mov 104 KB] [.mov 7.3 MB]
neck flexibility, whole body sheathed in a visual representation of the distribution of mass [.mov324 KB] [.mov 2.9 MB].