According to scientists, their long necks were probably more like that of an ostrich with only a limited amount of movement, News.com.au reported.
In the BBC series 'Walking with Dinosaurs', huge sauropods such as diplodocus and apatosaurus are depicted with flexible necks that allowed them to reach for tree-tops and low-growing vegetation.
But the portrayal, based on computer simulations, is likely to be inaccurate, the study authors claim.
Previous estimates of sauropod neck flexibility have focused largely on the neck bones and failed to take account of soft tissues such as muscle and cartilage, they point out.
The new research involved studying the anatomy of a distant relative of the dinosaurs, the present day ostrich.
It showed that increasing muscle mass reduced neck flexibility.
Variations in the distance between vertebral joints and the amount of cartilage present may also have stiffened sauropod necks.
Having less flexible necks could have restricted the range of foods accessible to the dinosaurs, the US scientists wrote.
The findings are published online in the journal Public Library of Science ONE.
--ANI (Posted on 15-08-2013)