On Mon, 23 Jan 2006 16:35:31 -0800, T. Michael Keesey wrote
Here's a thought: the greenest parts of a plant are generally at the top, right (where access to sunlight is unobstructed)? Thick-trunked, firmly-rooted plants growing in a very dense configuration could create a barrier for large animals that are unable to fit between the plants. Solution 1 would be for the animals to uproot the plants that are in their way, but this requires a lot of energy. Solution 2: the animals grow really long necks so they can reach out over the already-browsed trunks in their way and get at the greenery.
A long neck would also allow saurpods to feed for a certain distance into dense stands of trees which they'd otherwise not be able to penetrate at all (not without emulating a bulldozer).
Well, heh, I think sauropods could do that with little trouble at all ;)
If diplodocids had a prehensile tip to their tail, they could raise that as high as they wanted (no brain or windpipe to worry about) to tear down higher branches, then feed at ground level. In that case, the long neck might also be there to counterbalance the (hypothetical) long prehensile tail.