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Atlasaurus imelakei skeletal

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Atlasaurus imelakei

Etymology: "Atlas mountains lizard, the giant"

Time horizon: Middle Jurassic, Bathonian to Callovian epochs (~166 mya)

Length: 15.8m (52 ft.), perhaps more depending on maturity.

Probable mass: 20+ tons


*NOW UPDATED with more accurate femur and distal humerus data*

After several starts and stops, finally an accurate skeletal of Atlasaurus, the bizarre short-necked brachiosaur! This skeletal is piled beyond shoulder-high with data from the description paper as well as from photographs of the museum mount in Rabat, Morocco, which correct a lot of the errors found in GSP's and Michel Fontaine's awful interpretations.

Named for the Atlas mountains in its native Morocco, this odd early member of brachiosauridae is probably the strangest sauropod known from good remains besides Isisaurus - it broke all the rules of a group that was already smashing everyone else's conventions for body size and outrageous neck length. It was one of at least two early brachiosaur genera (the other being an unnamed Portuguese animal paleo-king.deviantart.com/art/… ) which pioneered the "giraffe-platform" model of arms longer than hindlegs that later became the signature feature of the entire family. Earlier macronarians, as well as more primitive sauropod groups such as Mamenchisauridae, already had their shoulders elevated somewhat above the hips, but much of this was due to their long shoulder blades (though few museums mount them at the correct incline). It was these "Atlasaurine" brachiosaurs which first featured arms where the humerus actually did tower over the femur, and the steep slope of the back was not due to big shoulders alone.

However, these early experiments with very long arms were a singular specialization. The very long necks typical of later brachiosaurs still had yet to appear. Atlasaurus was a very short-necked animal as far as brachiosaurs went, and even compared with more "average" sauropod families, the neck still looks painfully undersized. It's one animal that seems to be permanently designed for high-browsing, no matter what you like to imagine the neck doing. The arms are not just long but unusually slender, indicating that the muscles on the arms were relatively light, and that stride length, not torque, was basically the core of this animal's speed. For a sauropod it could have been surprisingly fast, its long arms giving it a clear balance and distance advantage over short-armed diplodocoids. The foot claws, larger than in later brachiosaurs, provided traction as well as flank defense. The tibia and fibula are short as in other brachiosaurs; by comparison the femurs look very oversized. The hands are still rather primitive for a brachiosaur, with the thumb metacarpal being shorter than the others (and, oddly, fused to the index finger's metacarpal), probably supporting a large swiveling thumb claw, a primitive feature which was reduced and fixed in later brachiosaurs. The posterior cervicals and anterior dorsals appear to have forked or at least partially forked spines as in Klamelisaurus, indicating that bifid brachiosaurs did exist but that the trait was later lost -which may coincide the the adoption of a more fully vertical and s-curved neck posture.

It's not clear why Atlasaurus didn't have a longer neck - even relative to more primitive sauropods it seems to have taken a step backwards in that regard. But the rock layers were it was discovered give a clue: the describers notes that the geology of the sandstone indicated "a vast plain close to sea level traversed by powerful rivers", which indicates the possible presence of large boulders getting pushed around by floods. It's possible that Atlasaurus lived on rocky floodplains where big herbivores needed a lot of vertical clearance to get over the huge stones and move quickly over collapse-prone ravines, but where most remaining trees were not very tall and long arms were sufficient for browsing height without needing a very long neck. Apparently the unfortunate type specimen (a teenager, like most of the best brachiosaur specimens) failed to make it over one particular ravine, and was partially scavenged by a theropod (which left behind some teeth) before being buried. It is a remarkably complete skeleton, including pieces of the skull, which appears to have roughly resembled Europasaurus, another basal brachiosaur. The medially curved humeri, as well as the angular front-heavy hips, are distinctly brachiosaurid, and resemble almost nothing else so much as B. altithorax, indicating that its lineage stretched back well into the Middle Jurassic, and that the basic axial and appendicular morphology of brachiosaurs as a unique group existed long before they reached their final iconic proportions.

And of course since this is Atlasaurus we're talking about, the scale figure this time is not Eugen Sandow, but Charles Atlas.


This skeletal has been credited as inspiration by:
cisiopurple.deviantart.com/art…
spinoinwonderland.deviantart.c…


REFERENCES:

M. Monbaron and P. Taquet. 1981. Découverte du squelette complet d'un grand Cétiosaure (Dinosaure Sauropode) dans le bassin jurassique moyen de Tilougguit (Haut-Atlas central, Maroc) [Discovery of a complete skeleton of a large cetiosaur (sauropod dinosaur) in the Middle Jurassic Tilougguit Basin (High Atlas, Morocco)]. Comptes Rendus de l'Académie des Sciences à Paris, Série II 292:243-246

M. Monbaron, D. A. Russell, and P. Taquet. 1999. Atlasaurus imelakei n.g., n.sp., a brachiosaurid-like sauropod from the Middle Jurassic of Morocco. Comptes Rendus de l'Académie des Sciences à Paris, Sciences de la Terre et des Planètes 329:519-526.
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anonymous's avatar
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shonisaurus's avatar
Eofauna, by the way. Do you have a projected future atlasaurus? It is a very rare sauropod and I think that to date it has not been represented either in vinyl, resin or PVC. It would be good news if Eofauna someday made a PVC atlasaurus like its palaeoloxodon antiquus, mammoth trogontherii and giganotosaurus carolini.
paleosir's avatar
paleosirHobbyist General Artist
Apparently there´s a 236 cm femur from the same general area and time as this animal. I don´t know what that femur exactly belonged to, but a close relative of Atlasaurus (or Atlasaurus itself) or Jobaria seems possible.

If that femur was indeed from an Atlasaurus, that would increase the upper size limit to ~19 meters and 30+ tonnes. What do you think of this?
cisiopurple's avatar
Hello paleoking, you have my great admiration for your work. I would ask your opinion about this paper and the cladogram proposed in it:

 Xing, L.; Miyashita, T.; Currie, P.J.; You, H.; Zhang, J.; Dong, Z. (2015). "A New Basal Eusauropod from the Middle Jurassic of Yunnan, China, and Faunal Compositions and Transitions of Asian Sauropodomorph Dinosaurs". Acta Palaeontologica Polonica. 60 (1): 145–154. 

In this work Atlasaurus is very close to Losillasaurus and Turiasaurus :| (Blank Stare) :( (Sad) :| (Blank Stare) 
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
Yes I do hear this contention a lot. However it is not immediately apparent just where they get the Atlasaurus data from. The description paper certainly doesn't give "344 characters" for Atlasaurus. I do not know whether someone flew to Morocco to analyze the bones for this or a previous cladistics paper. Where they got their Atlasaurus data from is hard to pin down. Also the paper's analysis has some other flaws like almost NO cladistic nesting in titansoaurs apart from Nemegtosaurus and Rapetosaurus, it seems to say that Malawisaurus and Alamosaurus are sister taxa or at least equally basal, which is flat-out WRONG. It also places mamenchisaurids as more basal than turiasaurids, Barapasaurus and Patagosaurus (odd), and also places them just above vulcanodontids on the the family tree (SUPER odd). Shunosaurus is almost a vulcanodontid but Spinophorosaurus is so much more derived? Something looks fishy here.

I can only say that I call them like I see them. And the photos I've seen of Atlasaurus indicate it's a basal brachiosaur or stem-brachiosaur. There is no way to convincingly argue that the humerus and femur shapes let alone the ilia are in any way "turiasaurid", unless a sub-clade of turiasaurs are showing some kind of crazy brachiosaur-like limb proportions and even morph-convergence in individual bones. Turiasaurus itself certainly doesn't exhibit any such brachiosaur-like convergence. Its bones clearly look very basal, "cetiosaur"-like for lack of a better word. The extreme asymmetry in the humeral head of brachiosaur, just isn't there in Turiasaurus. Other turiasaurs, I have not seen much of, but if the family is valid they would have to be similar, and not much like brachiosaurs.

So while  it's always possible I may be wrong about Atlasaurus, I doubt it... and for me to be wrong, i.e. for Atlasaurus to be a turiasaurid, it would take a big revision of turiasaurs as a family... Turiasauridae itself would have to be broken up and declared polyphyletic, artificial, void in Puerto Rico and Guam, and all that fun stuff. Turiasaurus itself is clearly a very different animal from Atlasaurus, their bones don't even look like things that would belong in the same family.
cisiopurple's avatar
Fantastic! thank you very much. You convinced me. At the moment we can assume that saltasaurus is closer to brachiosauridae than other families :) (Smile) :) (Smile) 
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
Well not quite.

Brachiosauridae is technically related to the titanosaurs, and is obviously much closer to them than things like diplodocids (which were sometimes mistakenly assumed to be closer to titanosaurs due to misinterpreting convergence in the specialized skull of Antarctosaurus - but that was over 80 year ago!) It's been known that titanosaurs are closer to brachiosaurs than to diplodocids for a long time, at least since the 70s with Powell and Bonaparte, but this was only fully confirmed by complete skull and tooth material in the last couple of decades with the preparation of Malawisaurus and Rapetosaurus.

But even so, Brachiosauridae isn't a true titanosaur family, and is a lot more basal than saltasauridae. Brachiosaurs are at the basal end of titanosauriformes. True titanosaurs are at the derived end. Saltasauridae is in turn the most derived group of these titanosaurs (or second most derived, after Nemegtosauridae, depending on who you ask), all the way at the "upper end". There are several transitional families (i.e. chubutisaurs, euhelopodids, etc.) between brachiosauridae and the most primitive true titanosaurs, and then from there you still have a lot of basal and intermediate titanosaur families before you get all the way up the evolutionary tree to saltasaurids.

Here is my rough family tree for titanosauriformes: paleo-king.deviantart.com/art/…

Brachiosauidae is at the bottom end. You can see there are a lot of transitional families before you get to Saltasaurus. My point is that the paper you mentioned basically nests all titanosaurs together as a hub-and-spokes arrangement, and thus probably doesn't include enough derived characters to properly sort them out into a real accurate family tree with basal and derived groups. Malawisaurus and Nemegtosaurus are so different it's not even funny, there is a lot of evolutionary distance between them, with Malawisaurus being much more basal. Of course brachiosaurs are even more basal and more distant.

Keep in mind this tree is constantly being revised but so far is very consistent with the visual data. It is just about titanosauriformes, not all sauropods. It doesn't include every titanosauriform species but does have the taxonomically important described ones.
cisiopurple's avatar
I fully agree! Thank you very much for the explanation and for your reference to the family tree of titanosaurs, which I find extremely helpful in understanding the evolution of these beautiful animals. In this field, you really are the number one :) (Smile) :) (Smile) . However I intend to apologize for the misunderstanding: I meant atlasaurus and not saltasaurus. Probably the spell-check has turned the word into the most common term, and I have not checked. So I intended that atlasaurus (ie the dinosaur in question) is close to brachiosauridae (not  Saltasaurus). Sorry again. :( (Sad) 
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
Ahh ok.

Then you are right. Atlasaurus does appear to be closer to brachiosauridae than any other family. The femur, humerus, hips, all scream "proto-brachisoaur". The dorsals are very close to those of Europasaurus, which had a similar skull too.

It's still hard to tell whether Atlasaurus or the Klamelisaurids are more basal in the evolutionary lead-up to "classic" brachiosaurids, but I suspect the latter is the case due to their more modest arms and fewer Europasaurus-like features. Which means that very long necks evolved more than once in the greater "brachosauroidea" and that long arms likely evolved in true brachiosaurids before crazy-long necks. Or that Atlasaurus was just a weird outlier that shortened the neck more than its mainline relatives, while still being among the most basal brachiosaurs to have the very long arms (its hand is still rather basal with the thumb claw off the ground like klamelisaurids and other basal neosauropods).
cisiopurple's avatar
Nod Very interesting Nod !
paleosir's avatar
paleosirHobbyist General Artist
Hello Paleoking:

I have heard some people say Atlasaurus could also be a turiasaur, what is your stance on that?
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
I have heard this rumor, and it smells... not saying it's impossible, but it sure smells. Everything I have seen of the appendicular and pelvic elements of Atlasaurus looks distinctly brachiosaurid... a lot like B. altithorax, just more primitive. Turiasaur humeri don't look much like those of Atlasaurus. Also the ilia and femurs of Atlasaurus look more brachiosaur than anything else.

However some "Turiasaurs" like Zby may have converged on Atlasaurus in proportions.
paleosir's avatar
paleosirHobbyist General Artist
Oh, thanks!
That clears up a lot.
paleosir's avatar
paleosirHobbyist General Artist
A really interesting sauropod, also that piece about it's environment is very interesting and inspired me for drawing it :)
As far as speed goes: speed estimates for derived, huge brachiosaurids were like 20 km/h at max, so I am putting this one at 25 to 30 km/h if generous, maybe.

I'm fascinated by this animal.
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
Yes it's a very interesting species. Abrosaurus and Tadouzasaurus may have looked very similar.
paleosir's avatar
paleosirHobbyist General Artist
Ok
MuseumDancer's avatar
I love this illustration! Would I be able to use it for some text panels at the Zuhl Museum: Home of the Zuhl Collection in Las Cruces, NM. I am the director. We are a small museum specializing in Petrified Wood, fossils and minerals. Recently our benefactor donated a 7ft Atlasaurus femur and I would like to have an accurate depiction of the animal's size and skeletal structure. We do not charge to visit our museum and run almost entirely on donations so we can not really afford to purchase art work for our text panels. Please let me know and if yes, how would you like us to format your credit footnote on the text panel. Thank-you! 
northafricandinosaur's avatar
please do someone know the predator of atlasaurus .
thediremoose's avatar
Afrovenator lived around the same time in Niger, which isn't that far away.
bLAZZE92's avatar
I was reading the recent Qijianglong's description paper and was surprised that they recovered Atlasaurus as a turiasaur, then I checked D'Emic 2012b and it appears that it has never been recovered as a brachiosaurid in a phylogenetic analysis, what makes you think it really is a brachiosaurid?
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
The hips are unmistakably brachiosaurid, as are the humeri and femora. Honestly I see a lot of features of Brachiosaurus itself in this animal, particularly in the ilium shape. Furthermore there is another very similar brachiosaurid known from Portugal (as yet unnamed) whose hand structure is far more derived than Turiasaurus.

If your look at skeletals of Turiasaurus (like that by Asier Larramendi) it looks nothing like Atlasaurus. Turiasaurus doesn't have the crazy-long arms or high shoulders, its skull is rather different and its length is overwhelmingly tail (much like Patagosaurus).

Of course if what we really have it a brachiosaur that fell on top of a turiasaur and got buried in mud, that would be interesting. But it still wouldn't explain the crazy-long forearms, the humeral head shape, the front-heavy hip structure, or the near-cylindrical arrangement of the metacarpals.
thediremoose's avatar
Actually, regarding possible North African turiasaurs, I've been wondering if Jobaria might be a turiasaur for quite some time. The skull looks identical to that of Turiasaurus and some details of the scapula are similar as well. Plus its position at the base of Neosauropoda is very close to Turiasauria.

Of course, Jobaria also has similar issues as Atlasaurus; Sereno only gave it a brief description and probably won't get back to it for a long time.
Paleo-King's avatar
Paleo-KingProfessional Traditional Artist
At least Atlasaurus had a better description paper than ANYTHING Sereno seems to be capable of. He's mainly a NatGeo "glitz and hype" paleontologist. Likes to get down in the dirt and dig up lots of bones, like a dino-Indiana Jones. But as for taking the time to do advanced morphometrics or even draw accurate diagrams of the bones, let alone classifying species, forget about it. Sereno has more digs, photo shoots and of course TV spots to do. Jobaria looks like a "camarasaur" so he assumed that's what it was, but also misdated the rock (largely assuming that Afrovenator, found in the same layers, was some sort of advanced cretaceous allosauroid). But no Camarasaur lived in the cretaceous! But then it turned out it's even more primitive than camarasaurs and his dates were something like 60 million years off!
thediremoose's avatar
Yeah, exactly. And now we have what could be the only really complete turiasaur that could be a very useful reference in reconstructing the fragmentary European specimens... but it's never going to be properly published as a result of the author always having other things to do.

...and of course Afrovenator turned out to be a megalosaur, which axes even the original idea on dating it.
anonymous's avatar
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