Brachiosaurs are instantly recognisable dinosaurs, with their long necks bending around the trees - but is this the right way to imagine them?
Dinosaurs like these belong to a group called the sauropods, along with the Diplodocus and the Apatosaurus.
Until now experts have thought these creatures had really flexible necks that allowed them to reach high to munch on leaves, but also to bend low to nibble at the bushes.
But now scientists think those long necks weren't as bendy as we'd thought.
It is a flightless bird - the ostrich - that has led scientists to now question just how flexible dino necks were.
Ostriches have long necks that help them bend down to the ground.
So, by studying them a team of researchers in the US think they've now got a better idea of how dinosaurs moved.
Bones and muscle
When studying dinosaurs palaeontologists (dinosaur experts) have to base much of their studies on the fossilised bones.
The skeletons of sauropods suggest their backbones were pretty flexible, but this doesn't take their muscles into account.
By studying muscle movements of ostriches the scientists are able to imagine the sorts of muscles the sauropods would have around their necks.
The sauropods 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.
This lack of flexibility may have restricted the range of foods the dinosaurs could reach.
And they may have had to work harder for their food - each hefty herbivore needed about 400kg of plant-based material every day - that's about the weight of five adult men!
Matthew Cobley, leader of the research team, says: "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."
He added: "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."