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.
Highlights
The elongated neck of sauropod dinosaurs is one of their more notable features
Since the scanned skeleton of the newborn giraffe comes from an articulated dead specimen (Fig 2A and 2B), we made the following observations of the scan before digitally separating the bones: (i) the intervertebral space between cervical vertebrae and caudal vertebrae pairs (Fig 2B–2D) is much greater than the one between dorsal and sacral pairs. (ii) There is an ossification body in the anterior centrum of most cervical vertebrae
This body may be slightly separated from the actual condyle but is usually connected by an ossified constriction in most vertebrae (Fig 2F–2H). (iii) The mineralized bone matrix of some cervical vertebrae is asymmetrical, that is, one of the sides is more ossified than the other. (iv) The pose of the neck, flexed ventrally and laterally to the right with some torsion, makes the head reach the torso and required the left pre- and postzygapophyseal facets to be completely disarticulated from Axis-CV3 to CV6-CV7 joints (Fig 2C)
Summary
The elongated neck of sauropod dinosaurs is one of their more notable features. The digital fossils used to build the virtual skeleton are deposited at the Museo Paleontologico de Elche. The newborn giraffe CT-scan data is deposited in Morphosource (https://ea-boyerlabmorphosource-01.oit.duke.edu/Detail/MediaDetail/ Show/media_id/9312)
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