DrScottHartman's avatar

La Rioja's ponderous biped

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Riojasaurus has been described as being quadrupedal, like Melanorosaurus is (at times it has also been grouped with Melanorosaurus, but now it's usually recovered as more primitive than melanorosaurids). The hand would do a better job of supporting weight than plateosaurid-grade prosauropods, but it's still not made for striding. Likewise, though the limbs are indeed closer in size to one another than say Plateosaurus, the relatively straight back and largely immobile shoulder girdles don't support the idea of them moving around on four limbs when they wanted to go anywhere. 
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anonymous's avatar
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Megalotitan's avatar
relating to the comment right below about PULR 56, how much of this skeletal would be the holotype?
Ornithopsis's avatar
What do you think of the suggestion that ULR 56 is distinct from Riojasaurus?

It's been hinted at a few times in recent prosauropod phylogeny papers such as McPhee and Choiniere 2017. Taking ULR 56 out of Riojasaurus moves the genus up into Sauropodiformes, so maybe ULR 56 is something basal. It would explain a lot about the skull shape.
DrScottHartman's avatar
Sorry about the late reply - I think it's entirely possible, but will probably leave it in the skeletal until someone formally refers it to another taxon.
ProcrastinatingStill's avatar
Quick question Scott. At what point in Sauropodomorph history would you say experimentation with quadrupedalism or falcutative bipedalism began?
Atlantis536's avatar
Weird. I clearly remember that Riojasaurus was quadrupedal.
DrScottHartman's avatar
In the '90s Greg Paul normalized portraying almost all prosauropods as quadrupedal. Biomechanics papers suggest that it's actually not terribly common until you get close to saurorpods.
Megalotitan's avatar
Is the neck just proportionally short or does it have less cervical vertebrae than other primitive sauropodomorphs?
DrScottHartman's avatar
It depends on which other primitive sauropodomorphs you are talking about.
Megalotitan's avatar
All sauropodomorphs closer to Plateosaurus than to Panphagia.
DrScottHartman's avatar
It's not any proportionately than Aardonyx, or even necessarily Sellosaurus (aka P. gracilis), it's mostly just a much more robust neck, which I think helps make the neck appear shorter. For really long-necked taxa like yunnanosaurs the difference is in the length of the individual cervicals, not in their vertebral count. "Prosauropods" were a pretty widespread group, so it's probably not surprising that we see this sort of variation in response to local differences in selective pressures (feeding, behavioral needs, etc.).
ijreid's avatar
That is one weird shaped head
DrScottHartman's avatar
YEt it's beautifully preserved, so the weirdness is real :)
Medenadragon's avatar
Ah, question for you: will there be/is there a paper on this new stance? I'm working as the concept artist for a book which will be featuring as accurate as possible dinosaurs, and the writer wants to have some clarification on the new stance.
DrScottHartman's avatar
So there have been a lot of papers looking at prosauropod stance, but not specifically on Riojasaurus. Still, aside from believing in my mad skeelz as a skeletal drawing-er, bipedalism is pretty well bracketed in Riojasaurus. Papers by Bonnan & Senter and later by Mallison showed conclusively that the more primitive Plateosaurus was clearly bipedal, and later papers looking at the more advanced Massospondylus and Adeopapposaurus, and even the quite advanced Aardonyx all show they were bipeds (with the latter making some changes to the hind feet to shift towards graviportalism even before the switch to full-time quadrupedalism!). It doesn't look like you get quadrupeds until you get way up to melanorosaurids at the base of Sauropoda. 

So what gives with Wikipedia? Well Bonaparte described it as an obligate quadruped originally, and the only two attempts at a skeletal reconstruction since (Peter Galton and Greg Paul) both restored it as a quadruped (though Galton's doesn't look terribly comfortable in the pose). So without an explicit paper Wikipedia's editors presumably just didn't change anything. But from a phylogenetic bracketing case it would be surprising for Riojasaurus to have been quadrupedal (same with Yunnanosaurus, or any of the massospondylids like Lufengosaurus). 

I wasn't married to the idea either way of course - it's not crazy that there could be more than a single origin of quadrupedality in basal sauropodomorphs (Anchisaurus may or may not end up being an example of that), but the bones didn't support a quadrupedal animal, so the above result is what you get :)
Medenadragon's avatar
I see, thanks for the info! I'll be sure to pass it along to my boss. :)
Medenadragon's avatar
Ahhhhh this makes me so happy! I finally can make a proper Riojasaurus reconstruction! That's so cool though that it's actually a biped. everywhere else says it's quadruped, though you make a much more reliable source then Wikipedia for sure. XD 
Philoceratops's avatar
Can you do Zuniceratops, Yi, Dimetrodon, Carnufex, Placerias, Chilesaurus, Pterodaustro, Postosuchus, Tarbosaurus, Ankylosaurus, Euoplocephalus, Quetzalcoatlus sp., and Yutyrannus please?
DrScottHartman's avatar
Sorry, I'm not in a position to take requests. The ones I'm currently doing are for two publishing projects I'm working for, and then I will be on skeletal hiatus until the summer so I can work on my dissertation. Though one or two from your list are done and will be released at an appropriate time.
Yutyrannus's avatar
I know what the first one is, is the second one maybe Yutyrannus?
PedroSalas's avatar
That's a cute propsy.
Those seventh and eighth cervical vertebrae slightly protruding under the ribs are weird.
ZEGH8578's avatar
Oh wow, that's one un-elegant looking animal
Now, I know poor Riojasaurus can't help looking like that, but wow
ShadowoftheEast's avatar
Another great reconstitution! It's always a pleasure to discover your news technical drawings! Even more interesting, the amount of useful informations you give to each of your skeletons is very reliable! :)
anonymous's avatar
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