The occiput of Amargasaurus (Sauropoda, Dicraeosauridae): Reconstruction of the craniocervical muscular insertions with comments on feeding strategy

Abstract

Sauropods were the most gigantic land animals that ever lived on the Earth, and dominated herbivorous niches in many terrestrial ecosystems from the Jurassic to the end of the Cretaceous. Other than their great size, the elongated neck was the most remarkable feature of the sauropod bauplan and has been suggested as a key factor underpinning their evolutionary success. The necks of dicraeosaurid sauropods are particularly unusual, exhibiting extremely long neural spines and often being relatively short for sauropod necks, rising questions about their feeding strategies. In this regard, there are still many unknowns regarding the structure and function of the sauropod neck, especially concerning the soft tissues. Craniocervical muscles are particularly important, since they are responsible for the movement of the head relative to the neck, strongly implied in the feeding behaviour. The braincase of Amargasaurus cazaui, a dicraeosaurid from the Lower Cretaceous of Argentina, represents a chance to reconstruct the craniocervical muscles in a sauropod and, in turn, shed light on the feeding behaviour.. In this study, the insertions of the muscles are reconstructed using the Extant Phylogenetic Bracket (EPB) approach, based on the anatomy of extant archosaurs and then compared with other studies performed on other groups of dinosaurs. There are several differences due to the disparity in the identification of the attachment areas and/or differences in the homologies of the muscles of the extant archosaurs. In the light of our findings, we discuss the high and low browsing modes for food acquisition and propose a 3 steps mechanism to explain the importance of the craniocervical muscles during animal feeding. This contribution represents the first complete reconstruction on the neck muscles inserting in the occiput for Dicraeosauridae.