More on sauropod necks

["David Marjanovic" <david.marjanovic@gmx.at>]

Why is it so difficult to get one's own text in black when the answering to dark blue?

I wanted to check and see if they were right. I used Gilmore’s Apatosaurus monograph and drew each individual cervical and lined it up with the next, and guess what, the front of the neck turns DOWN!!! So they are right.

No problem with all diplodocimorphs, especially Apatosaurus and dicraeosaurids, having downward-aiming necks. (Though I think rearing up into the famous tripodal stance should have been possible, but that doesn't affect the neck.)

>>David M wrote

 

I've got the opportunity to read this interesting paper. It concerns only Giraffatitan brancai and no other sauropods, about which it only includes cautionary notes about diversity. It arrives at the conclusion that G. held its neck vertically by measuring the areas of the intervertebral disks and calculating stresses. Unlike the paper that concludes that all sauropod necks were horizontal (ref later if needed), it considers the cervical ribs resistant against tension -- so that the head didn't fall on the back -- rather than as resistant against compression and providing the ventral bracing of a beam.<<

The italics change into Times New Roman? Cool.

Whats the paper?

As HP Stephan Pickering just wrote:

 

Andreas Christian & Wolf-Dieter Heinrich wolf-dieter.heinrich@rz.hu-berlin.de: The neck posture of Brachiosaurus brancai, Mitteilungen aus dem Museum für Naturkunde zu Berlin, Geowissenschaftenliche Reihe 1, 73 -- 80 (19 November 1998).

 

The other, that argues for horizontal necks, is

 

John Martin, Valérie Martin-Rolland & Eberhard Frey: Not cranes or masts, but beams: The biomechanics of sauropod necks, Oryctos 1, 113 -- 120, October 1998

 

I've got both via swapping -- especially Mitt. Mus. Natkd. Berl., Geowiss. Reihe is difficult to get, and I can't probably get Oryctos either.

And what intervertebral disks? I didn’t know anywhere preserved.

Of course not. Abstract of the first:

"Compressive forces acting on the intervertebral discs [always that c/k problem in English... is there any rule?] along the neck of Brachiosaurus brancai from the Late Jurassic of Tendaguru are calculated for different neck postures. The distribution of compressive forces along the neck is compared to the distribution of the cross-sectional areas of the i[...]. Neck postures in which the pattern of compressive forces does not match the pattern of cross-sectional areas of the i[...] are rejected. The neck posture of B[...] must have been nearly vertical. A more inclined neck posture can only occasionally have been kept. Therefore, B[...] appears to have been an extremely specialized high browser. In the same area, different sized individuals fed in different heights instead of each individual exploiting an extended vertical feeding range."

 

From the text:

"The transversospinalis muscles of Diplodocus carnegii [sic] were barely able to lift the neck from a horizontal to a vertical position, as demonstrated by Alexander (1985). [Ask me about all full refs if necessary.] Even with the possible help of the longissimus and iliocostalis muscles, lifting the neck seems to hav been a strenuous activity for this dinosaur."

 

"According to Janensch (1950a), there are 13 cervicals in B[...]. Centra and spinal processes are preserved in the cervicals 3 to 5 and 8. The spinal processes of all other cervicals are reconstructed. The centra of cervicals 9 to 13 are preserved."

 

"Method

 

Neck, trunk, and tail of an animal experience forces and torques (bending moments) depending on its posture and the distribution of body mass. [...] The pattern of bending moments along the vertebral column depends on mass distribution, posture, and forces exchanged between the animal and the substrate (ground-reaction-forces).

    In the neck, bending moments are usually highest at the base and drop towards the head. However, the neck experiences very little [...] or no bending moments at all with a more or less vertical posture. The bending moments M can be calculated according to the rules of statics (Pauwels 1965). In this study, the calculations of bending moments along the neck of B[...] are based on the mass distribution determined by Gunga et al. (1995). These data allow to calculate the bending moments and the weight forces at 10 locations along the neck which do not match the positions of the intervertebral discs. The bending moments and weight forces at the locations of the i[...] were obtained from these data by linear interpolation.

    As long as the neck is not oriented backwards, bending moments along theneck must be counteracted at the intervertebral junctions by tension in [...] muscles, tendons, or ligaments that are located dorsally to the vertebral centra (Preuschoft 1976, Alexander 1985, 1989, Christian & Preuschoft 1996).

    [lots of maths and biomechanics]

    The pulling force F(m) [m as an index] of the epaxial muscles evokes a compressive force of the same magnitude between the vertebral centra (Preuschoft 1976). The total compressive force F acting on an i[...] is the sum of two components: first, the muscle force F(m) due to the bending moment M, as described above, and second, the weight force F(g) of the fraction of the neck cranial to the regarded position multiplied by the cosine of the angle phi between the plane of the i[...] and the horizontal plane (see Preuschoft 1976):

 

F = F(m) + F(g) x cos phi.

 

The highest regularly occurring compressive forces F along the neck should be proportional to the transversal cross-sections of the centra or of the i[...], under the assumption of equal safety-factors (the thin and elongated cervical ribs are not suitable for transmitting high compressive forces onto the vertebral centra) [my emphasis; contra the second paper, which calls them the ventral, compressive bracing of horizontal necks]. The transversal cross-sections A of the i[...] may be the better measure for the compressive forces and can be estimated from the diameters of the surfaces of the adjacent vertebral centra (Preuschoft 1976). [...] A of each i[...] was calculated by assuming an elliptic shape with the lateral and the dorsoventral diameters of the caudal surface of the adjacent vertebral centrum as major axes (Preuschoft 1976, Christian & Preuschoft 1996). The measurements were taken from the scaled illustrations of the vertebrae by Janensch (1950a). In the case of obvious and critical deformations, however, the surface was reconstructed. The relative error in determining [...] [A] was estimated to be about 10%. The distances of the i[...] from the occipital condylus were measured along the vertebral centra. The measurements were taken from the scaled illustration of the completely reconstructed skeleton by Janensch (1950b).

    To decide which neck posture was habitual in B[...], the distribution of [...] F was calculated for three different hypothetical neck postures (see below). For each posture, the distribution of compressive forces along the neck was compared with the distribution of [...] A of the i[...]. The neck posture was rejected if both distributions did not match.

    The following three hypothetical neck postures were analysed: In the first model, the neck was assumed to be fully stretched out in a horizontal plane with the head pointing forward (in the following refer[r]ed to as "horizontal neck posture"). In the second model, the neck was positioned as in the reconstruction by Janensch (1950b) with the middle fraction of the neck forming an angle of about 30° with the vertical ("mounted neck posture" [...]). In the third model, the same shape of the most cranial three quarters of the neck was used as in the reconstruction by Janensch (1950b) but the neck was rotated around its base [along with, in the figure, the first 3 dorsal vertebrae] so that the straight middle part of the neck is fully vertical ("vertical neck posture" [...])."

 

I'll write later about the results, the post is really long enough, and I must go to bed. See... read you next year :-)