Virtual range of motion analysis of the neck of Amargasaurus cazaui (Sauropoda; Dicraeosauridae).

VIDAL, D.; SERRANO-MARTÍNEZ, A.; WINDHOLZ, G.J.

Madrid

Congreso; 4th IMERP Program and Abstract; 2018

Amargasaurus cazaui, a dicraeosaurid sauropod from the Lower Cretaceous of Neuquén (Argentina) had extremely elongated and forked neural spines, a notable condition among its group. This peculiar combination of extremely elongated neural spines with an orientation ranging from slightly anteriorly oriented in the posteriormost cervical vertebrae to a quite posteriorly inclined mid to anterior ones has led to propose several functional hypotheses. In order to test them, we have conducted a range of motion analysis using high-resolution 3D photogrammetric scans of the original fossils. In order to measure heights and angles in relation with the body, we have digitally mounted all preserved fossils. The osteologically induced curvature of the dorsal series, not very well preserved, compares favourably with the exquisitely preserved dorsal column of Brachytrachelopan mesai (another dicraeosaurid). On our reconstruction, the snout is at 1.98 m from the ground in osteologically neutral pose (much higher than the 0.70 m obtained in previous studies). The prezygapophyseal facets are extremely large and elongated in all cervical vertebrae up to the cervicodorsal transition, substantially more than in Brachytrachelopan or diplodocid species. Dorsiflexion is limited due to the elongated, posteriorly directed spines, whereas ventriflexion is not. Ventriflexion allows the snout to reach the ground without dislocation or flexing/ abducting the forelimbs, while maximum dorsiflexion allowed a maximum height of 4.5 m. This implies Amargasaurus was a medium to low browser, as previously proposed. A greater intervertebral flexibility than in other diplodocoids, many of which (i.e. Nigersaurus) have also been interpreted as low-browsers, support the absence of a double sail in the neck of Amargasaurus. It also supports the ability to perform potential display and/or agonistic behaviors in this taxon.