The Chubut Monster is officially named!

Posted by Nima On Thursday, August 10, 2017 2 comments

Today the Chubut Monster, possibly the largest dinosaur known, has been published.

There are apparently six specimens from the same site. The largest of them may have exceeded 120 feet in length, and though the paper proposed a maximum mass of 82 tons, I suspect that when restored with the correct rib curvature and soft tissue levels, this animal may have exceeded 110 tons.

The AMNH mount, which is entirely made of fiberglass replicas, appears to be based on the holotype and a few similar-sized specimens. These are still smaller than the individual represented by the gigantic femur on the forklift pallets.

Patagotitan mayorum is build like something between Argentinosaurus and a lognkosaur, with traces of Malawisaurus-like features as well. Though the cladistic analysis in the paper is odd to say the least (taking Rinconsaurus and most other aeolosaurs out of Saltasauridae and making them sister-group to lognkosauria, and throwing Argentinosaurus into lognkosauria, while throwing Malawisaurus into a derived lithostrotian cluster!) it does make two very interesting points; not only is the new Chubut Monster Patagotitan related to Argentinosaurus, but Ruyangosaurus is classed as a titanosaur more derived than Andesaurus.

It seems ironic that the paper does not draw a closer relation between Patagotitan and Ruyangosaurus, because the morphology of their posterior dorsal vertebrae appears almost identical. The oddly leaf-shaped neural spines, the many shallow and thin laminae, and V-shaped prezygapophyses so recently having lost the hypantrum, are very similar to those of Patagotitan, which still retains a small hypantrum in a few of the mid-dorsals. The slender neural spines of the caudal vertebrae recall Mendozasaurus. The centra of the dorsals resemble Malawisaurus to some extent, and Argentinosaurus from certain angles. It's looking like Patagotitan occupies a node on the titanosaur family tree somewhat more derived than Argentinosaurus, a direct descendant of the fork in the road between the "Malawisaurs" (Malawisaurus and Savannasaurus) and more derived groups such as the true lognkosaurs.

The biggest specimen of Patagotitan is known from a femur that both has the unusual proximal curvature of that of Ruyangosaurus, and a size exceeding the (reconstructed) length of the Argentinosaurus femur.

A terrible skeletal of Patagotitan. In reality the neck and back would have been steeper, and the tail likely less kinked downward.


Anonymous said...

I thought the mount in NYC is scaled to the largest individual, owner of the largest femur at 2.38 meters. I think the composite skeleton has humeri too small. The humeri is from a smaller individual. The larger individuals probably has humerus length comparable to Notocolossus, or maybe even larger. Based on the formula provided in Notocolossus paper you could get humerus length from 1.8m--1.9m for the in respect to the 2.38m femur.
The similarities between Patagotitan and Ruyangosaurus is very intriguing. I overlaid Ruyangosaurus holotype femur over Patagotitan femur and noticed Ruyangosaurus actually has a more "sharpened" lateral bulge, which also situates relatively higher on the femur. It really resembles more of Huabeisaurus and skinny version of Yunmenglong in proportion. I now wonder more if Ruyangosaurus is a chimera.
As of the posterior dorsal vertebra, they are indeed quite similar. Ruyangosaurus has smaller transverse process in comparison, while having an even more extensive accessory lamina stemming out of the pre and post spinal lamina. I wonder if this is a unique feature to the species, or represents a more derived feature amongst titanosaur.
Lastly, some of the Ruyangosaurus posterior dorsal vertebra are absolutely gigantic. The last dorsal/first unfused sacral (?) is 15% wider than the largest Patagotitan dorsal (anterior-mid dorsal). It makes me wonder whether Ruyangosaurus is more hind quarter heavy in that its posterior vertebra are the largest or the material consists of multiple individuals. It is hard to imagine a 68cm-wide dorsal centrum being the narrowest of the entire dorsal series.

Thalassophoneus said...

Hi, Nima. I do not have a Deviantart account yet and I just wanted to congratulate you for all of your work and mostly your recent remake of Argentinosaurus. I also attempted to estimate its neck length based on Rukwatitan a few days ago very quickly and I really appreciate that you made some more organised estimates. And the result is truly fascinating. I really love your work. You are my favorite skeletal artist.

In the past I have actually used your skeletals multiple times as reference. Without permission, the truth is, cause I didn't know how to contact you. I am a paleoartist. You can see my work here.
There might have been some cases were I posted a drawing based on a skeletal of yours without giving you credit. That is because I was pretty late to realize the importance of copyright. Now I do and I make sure to credit my sources (and to sign my drawings, cause I was not doing so until recently).

Anyway, that is all I had to say. Continue with your amazing work.

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