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Re: Sauropod Biology

From: David Marjanovic

Since trees don't grow horizontally, one would expect a Plateosaurus would stand upright at times to reach high branches.

One would expect it to get the neck into an upright position. But the rest of the body may or may not have been capable of withstanding such a posture.

Plateosaurus, Massospondylus and other Prosauropods were very front heavy animals, which is why they walked on all fours in the first place. They hand long necks, large heavy arms and big guts. I would imagine running around on two legs, with the torso pitched forward, would be even more of a stress than standing upright. The fact that many later (and far larger) sauropods retained this ability is certainly evidence that Prosauropods were capable of doing the same.

Why would it need special modifications to simply rest on the ground and support some of its weight?

Because of the sheer weight of the animal, the tail could get damaged otherwise.

Most of the weight would still be on the back legs. I'm not saying that these animals put ALL their weight on their tail. The tail was there as a counterbalance and possibly to take some of the weight. Obviously if this animal could stand on two legs, its certainly not going to need to put a whole lot of weight on its tail while upright! The tail would rest on the ground, and at the very least would help stabilize the body. The point is that these animals were very likely capable of standing upright to reach tree branches. Your argument does not make much sense when you consider the fact that the animal would be under less stress in an upright position then it would be in a horizontal position.

I thought they had died out by the end of the early cretaceous too, which is what I meant >>by "not long after the Jurassic".

The Early Cretaceous lasted for on the order of 50 million years, so I'd disagree about the "not" part. :-)

A very bad choice of words I admit = P But I consider the early cretaceous to be the first 1 3rd of the cretaceous, followed by the mid and late cretaceous. I'm still wrong though, even by my own definitions. the Brachiosaurs may have survived more than 50 my after the Jurassic. My point was simply that the extremely derived, high shouldered forms seemed to have gone into decline after the Jurassic.

And as Tim Williams wrote

Yes, that seems to be true. In that vein, Cifelli et al. (2000) gave _Sauroposeidon_ the species name _proteles_, meaning "perfected before the end".