Protohadros

Protohadros in a grazing pose.
The muscle bundles that follow the top of the neck, from the dorsal vertebrae, would stretch when in this pose, making the neck appear thinner, the muscles drawn out and hugging the length of the cervicals. When it raised its head again, to chew the mouth-ful, these powerful muscles would contract again, and "swell" the neck.

It could be that this development in Hadrosaurs coincides with their chewing battery, that prompted them to scoop up mouth-fuls, for then to lift their heads and chew, resulting in repeated up and down motions, that would require a specialized neck anatomy, while earlier ornithopods would merely "cut" the vegetation between their teeth *while* grazing, and therefore keep their necks mostly calm while they fed.

Finely chewed food has benefits in terms of energy efficiency, as the more "pulverized" the food - when swallowed - the more nutrition is extracted from it, before it comes out again. From what we know, Hadrosaurs did not have multiple stomachs, like cows, so instead they chewed the food untill it, quite possibly, was just juice and fibers left. With this kind of extraction, an animal can afford to spend time chewing, with its head raised from the ground. Efficient energy extraction also allows an animal to become, well, larger!

Humans have taken this to another level by burning and boiling our food, effectively destroying the tissues, breaking them up, and allowing us to just "token chew" a little, before swallowing it right down. This frees up energy allocation in our head, away from massive jaw muscles covering the whole top of our heads (compare to chimpanzees), to more brain!

Anyway, enough rant-musing... 

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DISCLAIMER:
Aaand someone has allready nabbed this pic for the "Land before Time" wiki, without asking permission.
I am _extremely lenient_ to giving permission to use my images, because HEY, I post them here, they're not water-marked, I don't demand money for my drawings, and so on

BUT PLEASE REFRAIN FROM BEING DICKS ABOUT IT, IS THAT TOO MUCH TO ASK?

Jesus tapdansing christ...