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Effect of intervertebral cartilage on neutral posture in necks of sauropod dinosaurs (revised)

Ben Creisler

A recently revised preprint paper in open access:

Michael P. Taylor  (2014)
Quantifying the effect of intervertebral cartilage on neutral posture
in the necks of sauropod dinosaurs. [version 2]
PeerJ PrePrints 2:e588v2
doi: http://dx.doi.org/10.7287/peerj.preprints.588v2

Attempts to reconstruct the neutral neck posture of sauropod
dinosaurs, or indeed any tetrapod, are doomed to failure when based
only on the geometry of the bony cervical vertebrae. The thickness of
the articular cartilage between the centra of adjacent vertebrae
affects posture. It extends (raises) the neck by an amount roughly
proportional to the thickness of the cartilage. It is possible to
quantify the angle of extension at an intervertebral joint: it is
roughly equal, in radians, to the cartilage thickness divided by the
height of the zygapophyseal facets over the centre of rotation.
Applying this formula to published measurements of well-known sauropod
specimens suggests that if the thickness of cartilage were equal to
4.5%, 10% or 18% of centrum length, the neutral pose of the
Apatosaurus louisae holotype CM 3018, would be extended by an average
of 5.5, 11.8 or 21.2 degrees, respectively, at each intervertebral
joint. For the Diplodocus carnegii holotype CM 84, the corresponding
angles of additional extension are even greater: 8.4, 18.6 or 33.3
degrees. The neutral postures calculated for 10% cartilage – the most
reasonable estimate – appear outlandish, but it must be remembered
that these would not have been the habitual life postures, because
animals habitually extend the base of their neck and flex the anterior
part, yielding the distinctive S-curve most easily seen in birds.