Diplodocus

home	paleontology

Diplodocus carnegii was modeled in DinoMorph™ along with Apatosaurus louisae in an early version of the software, with emphasis placed on modeling the articular facets of the neck, and not the postcervical skeleton. Since then the software has developed to permit more realistic modeling of osteology, and now this gracile sauropod has been given a more realistic appearance appearance. But like many other open-ended endeavors, there's always more to do, both in the sculpting and posing, but that will wait until the next time we need to attend to this taxon. In the following, the neck range of motion estimates are used to pose this updated version of the skeleton. While Apatosaurus, it's closely-related sister taxon has considerable ability to dorsiflex, the zygapophyseal design of Diplodocus simply does not permit much neck elevation, by the very shape, size and position of the zygapophyses.

The following illustration may help one to visualize two-dimensionally how I estimated dorventral flexibility after tracing the zygapophyses off of the actual mount of Diplodocus carnegii. The principles illustrated by the following were appled to limit the range of motion in the corresponding three-dimensional DinoMorph™ models.

Above are Diplodocus carnegii cervical vertebrae C13 and C14 (after Hatcher, 1901, pl. 4) showing estimated limits of the dorsoventral range of motion. In a, the right postzygapophysis of C13 is shaded, and the midline of prezygapophysis of C14 is indicated along with the center of rotation for dorsoventral flexion at the center of curvature of the condyle of C14. In b, the two vertebrae are placed in articulation and the dorsiflexion limit of 6° is illustrated, defined as that angular deflection which reduces the zygapophyseal overlap to 50% (note the anterior margin of the postzygapophysis of C13 is displaced anteriorly to the indicated midline). In c, ventriflexion is limited to about 8° (at which point the posterior margin of the postzygapophysis is displaced to the prezygapophysis midline). While the net effect, over the length of the neck of Diplodocus, is a limited abilty to dorsiflex (it probably did not raise its head much above the height of the shoulders), like Apatosaurus it appeared osteologically capable of ventriflexion sufficent to take the head below mean surface level, which we believe is shared by certain other sauropods that were specialized for lacustrine feeding. The overall effect is shown here:

The dorsal vertebral column is modeled as quite straight, with only a small degree of dorsal curvature, or arch, to the back. Here is a reconstruction from C10 to D10 based on Hatcher's original illustrations (with care to create a series with uniform scale, otherwise one creates a mess). Note that D4 was clearly sheared by postdepositional distortion in the original illustration, partly corrected in the below).

The above recontruction is supported by the following specimen (albeit with reconstructed centra), stored in the basement of the AMNH:

So the digital reconstructions I've made of Diplodocus have very little curvature to the back, which tends to make the neck nearly horizontal as it emerges from the shoulders. It is interesting that the neck itself, while straight at the base, appears to be intrinsically ventrally curved cranially (i.e., it droops, like every other sauropod neck I've reconstructed). The head, consequently, would have been held only a few meters above ground level in the undeflected state.

This sauropod was also studied in a replication of R. McNeill Alexander's estimation of nuchal ligament function in passively holding the neck in neutral position (he also concluded very limited dorsal flexibility for this taxon). See the SVP 2002 talk slides (in either QuickTime interactive .mov format or .pdf format) for more information regarding the following illustration.