Passage: On the basis of microtomography scans of skull elements of the holotype specimen, Sereno and colleagues created a "prototype" Nigersaurus skull they could examine. They also made an endocast of the brain and scanned the semicircular canals of its inner ear, which they found to be oriented horizontally. In their 2007 study, they stated that the structure of the occiput and cervical vertebrae would have limited the upward and downward movement of the neck and the rotation of the skull. Based on this biomechanical analysis, the team concluded that the head and muzzle were habitually oriented 67° downwards and close to ground level, as an adaptation for ground-level browsing. This is unlike the way other sauropods have been restored, with their heads held more horizontally.A 2009 study by the palaeontologists Mike P. Taylor, Mathew Wedel, and Darren Naish agreed that Nigersaurus was able to feed with the downturned head and neck posture proposed by the 2007 study, but contested that this was the habitual posture of the animal. The study noted that the "neutral" head and neck posture of modern animals does not necessarily correspond to their habitual head posture. It further argued that the orientation of the semicircular canals varies significantly within modern species, and is therefore not reliable for determining head posture. This was supported by the Spanish palaeontologist Jesús Marugán-Lobón and colleagues in a 2013 study that suggested the methods used by Sereno's team were imprecise, and that Nigersaurus habitually held its head like other sauropods.

Question: What was the purpose of the habitual 67 degree down turn of Nigersaurus necks?
for ground-level browsing