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February 20, 2008
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Plateosaurus engelhardti by ScottHartman Plateosaurus engelhardti by ScottHartman
Plateosaurus means "flat reptile", a name that was long poked fun at in the days of Godzilla-inspired upright postures. Then prosauropods suffered through a "they are all quadrupedal" phase (which I participated in), which still made a mockery of the name, as the position contorted the body so that the tail had to arc up into the air above the body. Well, it turns out that Plateosaurus-grade "prosauropods" used a low-slung subplantigrade bipedal posture instead which makes "flat reptile" not such a bad name after all...

Update: Brought the silhouette up to date. I went with the "fat tail" style contour for the ventral margin (the bottom!) of the tail, as many extant diapsids are like this, and with the low fourth trochanter and high transverse processes Plateosaurus is a prime candidate to have had similarly large caudofemoralis muscles.
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:icondinobirdman:
DinoBirdMan Mar 30, 2013  Student Artist
Looks like prosauropods has finally standing on two legs is didn't standing on all fours.
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:icondarthgojira:
I keep forgetting how short the front limbs are. While I'm sure that it could move quadrupedally, seeing the proportions here really shows them as bipeds.
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:iconscotthartman:
ScottHartman Mar 9, 2013  Professional Digital Artist
Actually the problem isn't with the arm length (although that would make quadrupedal movement slow at best), but with wrist mobility. At this point on the sauropodomorph tree the hands are stuck in a theropod-like "palms always in" position that makes quadrupedal locomotion basically impossible.

I'm not saying they couldn't crouch down on all fours, say if they wanted to eat something low to the ground, or duck down to hide under some (tall!) brush, but they sure weren't going anywhere on all fours, as there was no plausible stride.

BTW, this isn't just "hey I read the paper" talk (although there's some excellent work published on it), Heinrich Mallison and I spent a good couple of hours with a full 3D scan of an a Plateosaurus hand trying to get them to walk (I favored facultative quadrupedality at the time), and it just wasn't possible, despite enthusiasm for making it work.
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:icondarthgojira:
Fascinating. I didn't know that. I knew that the theropods had "palms in" posture, but it's new to me about prosauropods. I suppose the wrist rotated as they became heavier. This is really interesting. I wonder if there was a similar wristbending when ornithopods became semi-quadrupedal
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:iconscotthartman:
ScottHartman Mar 10, 2013  Professional Digital Artist
Yeah, the palms-facing-in thing is primitive for Dinosauria. There was indeed a similar inward bend in ornithopods on the way to hadrosaurs, but they never got as far (neither did ceratopsians), as both end up with something closer to a 45 degree inward cant to their hands, while sauropods get the hand facing a bit more inward (thought still never with the palms facing perfectly backwards).
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:iconblazze92:
I always thought that Plateosaurus had a goofy (if not ugly) head mmm, btw what's the thing below its jaw?
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:iconscotthartman:
ScottHartman Mar 8, 2013  Professional Digital Artist
It is a bit goofy looking in a way. The bone beneath the mandible is the hyoid - the bones that support the tongue muscles.
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:iconblazze92:
mmm I thought those were smaller, thanks.
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:iconaction-figure-opera:
The belly ribs, I don't know their proper name, what supported them other than muscle?
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:iconscotthartman:
ScottHartman Mar 8, 2013  Professional Digital Artist
The technical name is "gastralia", and nothing supports them except for muscles and ligaments, although in theropods at least they do overlap one another on the midline in a herringbone fashion.
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