Image caption A thick mass of neck muscle restricted the range over which the dinosaurs could reach

The familiar view of sauropod dinosaurs reaching out for vegetation using their long, graceful necks may not be entirely accurate, say scientists.

A study of modern-day ostriches suggests the ancient animals were probably quite stiff in their movement.

Sauropod dinosaurs had a thick mass of muscle in their necks and the researchers say this would probably have restricted the range over which the beasts could move their heads.

The study is published in Plos One.

Its authors say the findings have implications for the way we display the dinosaurs in museum exhibits and in the media.

Computer modelling that has been used to simulate sauropod movements will not have portrayed the lack of neck flexibility accurately, the team adds.

The largest animals Sauropod dinosaurs included the largest land animals that ever lived

Could weigh close to 100 tonnes - 10 times the record weight of a modern elephant

Very successful herbivores that arose in the early Jurassic and survived for about 100 million years

Fossil footprints show sauropods often travelled in great herds

Group included famous Diplodocus and Apatosaurus (formerly Brontosaurus)

Biggest was Argentinosaurus, a creature perhaps 30m in length BBC Nature - Dinosaurs

For example, the BBC's landmark TV series Walking with Dinosaurs modelled the neck movement using the position of the vertebrae.

But this did not account for the effects of soft tissues like muscle and cartilage, which this new study tries to incorporate by looking at ostriches.

The team, led by Matthew Cobley from the University of Utah, US, has shown that muscle mass reduces the maximum flexibility of ostrich necks.

The researchers measured the flexibility of the flightless birds with all their muscle tissue intact, and then slowly removed the muscles to test how this changed the situation.

As they are the largest birds to exhibit elongated necks, with vertebrae and musculature broadly comparable to those of sauropods, ostriches provide useful insights into the past.

"Previous studies looked at the skeleton on its own and the assumption was that flexibility is limited by the bones of the skeleton, but our study shows it's actually the soft tissue around it," said Mr Cobley.

He added that computer modelling of any biological system needed to be "ground-truthed" before it was accepted by the scientific community and presented to the public.

Image caption The long-necked ostrich gives scientists clues about its sauropod relative

"It's easy to be swayed by these beautifully reconstructed models of dinosaurs, but if these models aren't based on real, empirical data taken from living animals we can actually study, they only serve to confuse the general public."

The amount of cartilage in the neck and varying distances between vertebral joints could also have caused reduced flexibility, the research found.

A common sauropod picture in films and museums is a creature reaching from high tree-tops to food that's very low on the ground, but this new work could now change how the animals are depicted.

It suggest the lack of flexibility may have restricted the range of food to which the the dinosaurs had access. And they may have had to work harder for their food - the hefty herbivores needed about 400kg of plant-based material each day.

"Different sauropods were limited to different food types. It's why you don't see giraffes eating from bushes from the floor or goats eating from the tree-tops," Mr Cobley told BBC News.

"There was a better division of resources between dinosaurs, with the taller ones limited to taller trees and smaller ones to grazing bushes on the floor."

Michael Benton of Bristol University, UK, commenting on the research, said the study "provides food for thought" and a warning about reconstructing sauropod necks without considering the distribution of soft tissues.

"Formerly, people assumed a standard amount of soft tissue that would limit flexibility, but it is rather more complex, and some previous reconstructions of sauropod necks snaking around must be modified," Prof Benton told BBC News.