FORGOTTEN GIANTS, #3: Andesaurus

Posted by Nima On Monday, June 18, 2012 4 comments

Well after a LONG time, the Andesaurus project is finally finished - for a while at least. While the open-access issue has been very important, it's time to get back to what this blog is all about - dinosaur art and the science behind it. And Andesaurus is one of the few titanosaurs often touted as being record-breakers which have never gotten a decent restoration until now. This dinosaur is still pretty obscure though it's been known longer than Argentinosaurus, Paralititan, Sauroposeidon, and most of the other new favorites among giant sauropods. Strange, that this animal is literally the demarcation line at the base of titanosauria, universally acknowledged (though not necessarily correctly) as the most basal true titanosaur, extensively used as a key phylogenetic reference taxon in all sorts of papers, every paleontologist studying sauropods knows about it, and yet it's so little known in the public.

A rather fanciful drawing of Andesaurus delgadoi with a not-so-possible serpentine tail pose, and a very flat Diplodocus-like head (basal titanosaurs should actually be restored with large nasal crests, similar to Euhelopus and Malawisaurus).  Artist unknown.

Oh, and another thing. It's BIG.


Well maybe not that big. One of the first things you notice about Andesaurus (assuming one of those rare times when you do come across it) is that it's a titanosaur from Argentina. The second thing you notice is that like some other, far more famous titanosaurs from Argentina, its length is listed as over 30m or 100ft in those few books that actually bother to mention it (the only mass-published "layman's author" who seems to give it any attention is Dougal Dixon, in The Illustrated Encyclopedia of Dinosaurs). Andesaurus should be famous, then, if for no other reason than its size - any titanosaur a hundred feet long is pretty high up in the running for both longest and heaviest dinosaur. But don't hold your breath - this is all WRONG.

That's right, you heard me. DEAD wrong. Andesaurus isn't 100 feet long. Not even close. That length has been repeated in many places, Wikipedia among them (at least a few months ago). I don't know how many people have actually read the scientific literature on Andesaurus (which now includes the description paper, Calvo & Bonaparte 1991; the titanosaur comparative anatomy paper Salgado et. al. 1997; and an extensive redescription, Mannion & Calvo, 2011). And the number of people who have actually seen and measured the fossils, I could probably count on my hand. The dorsal vertebrae (what's known of them anyway) are absolutely dwarfed by those of Argentinosaurus - a bit odd for two creatures that were supposedly around the same size. Even plain old Brachiosaurus has bigger dorsals. Andesaurus is a lot smaller than we've been led to believe.

 Comparison of dorsal vertebrae of Andesaurus delgadoi and Argentinosaurus huinculensis in posterior and right lateral view, to the same scale. 
Seriously Mr. Dixon, one is only about half the size of the other!

Not that I knew that when I started drawing it. That's why I decided to make Andesaurus # 3 in my Forgotten Giants series (I'm starting from the biggest titanosaurs, in no particular order, then working my way down). In fact I assumed (before I was able to get my hands on the description paper) that Dixon's estimates would suffice for at least mapping out rough proportions. Not that it matters these days when you can digitally re-scale your sauropod, but it does get very confusing to check your measurements when everything you had believed about this creature turned out to be dead wrong.

The only photos of this beast that were available online were a couple of grainy mid-90s images...

                         Andesaurus delgadoi, posterior dorsal and two mid-caudal vertebrae.

Otherwise I had nothing to go on. Until 2010's SVP meeting in Pittsburgh, where by unexpected fortuitous circumstances I came to possess copies of both the description paper and Salgado et. al. 1997 (which actually has drawings of far more of the Andesaurus material). The resulting jumble of odd bone outlines was just enough to start piecing together this beast.

But inevitably some of the outlines were off. So it had to be redone.

A few reworks later, here's the progress. The little outlines outside the body are drawings of the bones from Salgado, et. al. 1997, scaled to the same scale. The pubis has no expansion at the tip - it just looks like a huge thumb.

Soon enough, a skeletal and a life profile began to take shape.
 And a front view...

And finally color tinting, shading of speculative missing bones, and inclusion of inset enlargements of the more interesting bits. This is literally all the known Andesaurus fossil material, all of it from the holotype (there are no other known specimens).

But all was not well in the Candeleros.... for one thing, this animal is colossal (at least in this initial version) and as we saw earlier, its vertebrae are only half as big as those of Argentinosaurus! Even the vertebrae of the Brachiosaurus holotype (which despite its huge size is only a teenager) absolutely dwarf those of Andesaurus. I scaled Andesaurus to 30m or 100ft initially due to having only Dougal Dixon's estimate and those two grainy photos to work from. But after obtaining the description paper and the Salgado paper, it became clear that the actual fossil material belonged to a much smaller animal.

Remember this picture? Andesaurus is NOT 100 feet long. Lets stop perpetuating size myths based on figures in non-technical commercial books which don't include any scale images of the actual fossils.

Andesaurus was no record-breaker. At most it was a mid-sized to moderately large titanosaur, with a tail of rather ordinary size and proportions, and no indication that its neck was exceptionally long for a sauropod either. There is an incomplete femur shaft, no shoulder material, and only a partial humerus, so limb lengths are speculative. Even the length of the torso is uncertain, since the anterior dorsals are missing. Indeed, it may have been only 50-60 feet long. 65 is a stretch. So it needed a rescale, among other modifications. Easy enough, since the scaling is based on the scale bar and human figure - they just had to look larger.


In addition to scaling down Andesaurus to the likely maximum size of the holotype, 66ft, I also bulked up the limbs, widened the torso, and added more fusion to the sacrals (perhaps still not enough, but we don't have the sacrals and the degree of sacral spine fusion varies among basal titanosaurs and titanosauriforms). 

Also I looked at Mannion and Calvo's new redescription paper of Andesaurus (unfortunately this paper is now paywalled by Wiley) - ultimately it didn't call for any major changes to my skeletal, though it did give me an idea of how laterally crushed the original fossils were (and how laterally compressed the tail naturally was even when you account for crushing). Finally, after a bit of checking the scale, I resized the Sandow figure to match up with his real height (depending on who you ask, about 5'9" or 5'10" which was relatively tall for his time).

In its original oversized form this was the first ever scientific schematic of Andesaurus, and now with the revisions, it's doubtlessly the best. All the scale bars have been corrected and rechecked.

And the title font is a little less boring. :)