Ontogenetic similarities between giraffe and sauropod neck osteological mobility

Abstract

The functional morphology of sauropod dinosaur long necks has been studied extensively, with virtual approaches yielding results that are difficult to obtain with actual fossils, due to their extreme fragility and size. However, analyses on virtual fossils have been questioned on several of their premises, such as the ability to accurately reconstruct intervertebral tissue with only skeletal data; or whether zygapophyseal overlap can be used to determine the limits of range of motion, since some extreme neck poses in extant giraffes have been claimed not to retain any zygapophyseal overlap. We compared articulation and range of motion in extant giraffes with the exceptionally well-preserved and complete basally branching eusauropod Spinophorosaurus nigerensis from the Middle (?) Jurassic of Niger, under the same virtual paleontology protocols. We examined the articulation and range of motion on grown and young specimens of both Spinophorosaurus and giraffes in order to record any potential changes during ontogeny. Also, the postures of virtual giraffes were compared with previously published data from living animals in the wild. Our analyses show that: (i) articulation of virtual bones in osteologically neutral pose (ONP) does enable accurate prediction of the amount of inter-vertebral space in giraffes and, roughly, in Spinophorosaurus; (ii) even the most extreme neck postures attained by living giraffes in the wild do not require to disarticulate cervical vertebrae; (iii) both living giraffes and Spinophorosaurus have large intervertebral spaces between their cervical centra in early ontogenetical stages, which decrease as ontogeny advances; and (iv) that grown specimens have a greater osteological range of motion in living giraffes and Spinophorosaurus.

Giraffes and hominins: reductionist model predictions of compressive loads at the spine base for erect exponents of the animal kingdom

“…We interpret 7 1,|| CT F as the compressive load on the C7/T1 IVD, which implies that this load is acting mainly perpendicular (normal) to the compensating structural (IVD) surface. As the anatomy of the cervical joints in giraffes is ball-and-socket-like (van Sittert et al, 2010;Vidal et al, 2020;Danowitz and Solounias, 2015), this implication generally seems well justified in these animals, and referring to a giraffe's C7/T1 joint, 'shear force' (see above) is a mathematical rather than a physical term.…”

“…The neck length is 1.55 m, and the "total height" (Mitchell et al, 2009) is the withers height (2.45 m) plus neck length (1.55 m) plus half of the head height (0.34 m), i.e. 4.17 m. These numbers have been measured in the original drawing of Vidal et al (2020, fig. 1).…”

“…Moreover, an estimate of the correspondingly predicted human intradiscal pressure is plotted (compressive stress 45 LL P times 1.4 (Nachemson, 1960;Brinckmann and Grootenboer, 1991)). Model-predicted force in the lumped torque-generating structure pulling past the IVD at the base of the giraffe's HENE or human HAT segments, respectively, versus forward bending (flexion) angle  of the respective spinal segment, with the centre of rotation being located within the base IVD, and 90 Tables Table 1. Dimensions of a giraffe extracted from van Sittert et al 2010; Vidal et al (2020), a man calculated by in-house software calcman2d (Hahn, 1993)…”

“…1 from the contour drawing of a giraffe in figure 1 of Vidal et al (2020) , including lengths and depths of the neck and the head at different body locations. These dimensional data were calibrated by the body height of a true-to-scale contour of a human depicted in the same figure in Vidal et al (2020) given to be 1.70 m. With all this, we estimated that the giraffe contour in figure 1 of Vidal et al (2020) represents a female specimen with an overall body length (‘total length’, Mitchell et al, 2009 ) of about 4.30 m and, thus ( van Sittert et al, 2010 , Table 1), weight of about 800 kg. For a 800 kg female, a cross-check using the ‘total height’ ( Mitchell et al, 2009 ) measure reveals that our number ( Fig.…”

“…For also fulfilling static torque equilibrium of the HENE segment, the torque exerted by via the lever arm R pull around the IVD joint compensates the external (bending) torque around this joint exerted by the HENE weight acting on HENE at its CoM:f Solving Eqn 4 for F pull and inserting this into Eqn 3, we find the load the IVD joint has to counter: We interpret F C 7/ T 1,|| as the compressive load on the C7/T1 IVD, which implies that this load is acting mainly perpendicular (normal) to the compensating structural (IVD) surface. As the anatomy of the cervical joints in giraffes is ball-and-socket-like ( van Sittert et al, 2010 ; Vidal et al, 2020 ; Danowitz and Solounias, 2015 ), this implication generally seems well justified in these animals, and referring to a giraffe's C7/T1 joint, ‘shear force’ (see above) is a mathematical rather than a physical term.…”