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[dinosaur] Argentinosaurus is still larger than Patagotitan

I sent this out as a PR. Sorry, no pretty pictures here. 

The release of the Carbillido et al. paper on the new super titanosaur sauropod Patagotitan has reignited the debate on what was the biggest dinosaur, the other contenders among titanosaurs being Argentinosaurus, Dreadnoughtus, Puertasaurus, Futalognkosaurus. all from the Cretaceous. 

Carbillidon et al. explicitly claim that Patagotitan is the largest species yet described, at 69 tonnes based on bone strength factors, using a methods of comparing the width and height of the trunk vertebrae to conclude it was larger than Argentinosaurus, etc. They further argue that titanosaur gigantism was unique. 

Press release summary -- 

The Carbillidon method of comparing traverse dimensions of the upper half of vertebrae to compare total animal size is entirely invalid. The proper comparison is the size of the centra, especially their length. The main bodies of the trunk vertebrae of Argentinosaurus are much larger and longer than those of Patagotitan, so the former had a trunk a fifth longer than the latter, and with virtual certainty must have been a larger titanosaur. 

A volumetric model indicates that Patagotitan had a mass of ~55 tonnes. This somewhat exceeds the volumetric model of Carbillidon et al., largely because they did not restore the hips (missing in the specimens) and belly to the correct enormous width typical of titanosaurs -- that the two estimates based on skeletal restorations are otherwise similar affirms the basic accuracy of the methodology. Being much longer trunked, Argentinosaurus probably massed at least 65 tonnes, and could have been substantially more massive.  

It is well documented that at any given combined humerus+femur circumference body mass varies by a factor of about two in living animals, so the 69 tonne estimate by Carbillidon et al. for Patagotitan based on that method is not reliable.

The contention by Carbillidon that Cretaceous super titanosaurs were exceptionally gigantic is problematic because there are indications of other similar sized sauropods. 

Estimating body dimensions and masses using new digital technologies is not superior to using traditional high fidelity ink pencil-ink skeletal restorations and clay volumetric models. 

Analysis --

Using most dimensions -- height and width of vertebrae, length and circumference of limb bones -- to calculate and closely compare the mass of animals is extremely unreliable because these factors vary widely relative to mass. The attempt by Carbillidon et al. to use a value derived from the height and width of the neural arch of titanosaur trunk vertebrae is therefore of no scientific value. 

The most important contributor to the total mass of a land animal, especially and herbivore with a big gut, is the trunk, the length of which is determined by the trunk vertebrae. Titanosaurs consistenly had 10 trunk vertebrae, or dorsals. The functional length of the dorsals in mm, total length of dorsal series measured from skeletal drawings attached in meters, and body masses from latter, are as follows. 

Argentinosaurus       390-430 mm   4.45 m  65+ tonnes 

Patagotitan               290-310 mm    3.7 m   55 tonnes

Dreadnoughtus         310-350 mm    3.7 m   34 tonnes

Puertasaurus               290 mm         

Futalognkosaurus        290 mm        2.8 m    25 tonnes

Giraffatitan                                                     32 tonnes
(a Jurassic brachiosaur closely related to titanosaurs)

With a main body about a fifth longer, and being a titanosaur with a broadly similar body form, Argentinosaurus could not have been smaller than or even the same size as Patagosaurus, it was larger, probably significantly. Nor does any other documented titanosaur come close to the dimensions and the bulk of Argentinosaurus

The Carballido et al. volumetric model based on digital technologies of 51 tonne estimate for Patagotitan is not markedly different from mine based on a rigorously measured skeletal drawing based in part on a side view photo of the mounted skeleton, and a clay model the volume of which was measured in water. Their shortfall in mass is clearly due to their showing an unrealistically narrow tail base in top view, and mainly on the hip and belly being too narrow -- not preserved in Patagotitan, the pelvis of Futalognkosaurus shown in the accompanying skeletal illustrations is typical for the group in being extremely broad, as was the ribcage immediately in front of it. That the two efforts at restoring the skeleton and soft tissues produced similar results supports the basic validity of using modeling as the best available means of restoring the mass of extinct organisms one the use of inherently unreliable bone strength factors, and finds no difference in the reliability of digital modeling versus hand drafting and modeling. 

Because Argentinosaurus is known only from some trunk vertebrae it's mass cannot be modeled. It can only be said that it certainly weighed more than Patagotitan, at least 15% more probably, or much higher.  

Patagotitan is more markedly more massive than Dreadnoughtus because the first has a deeper belly, and larger neck, tail and legs. 

The estimate based on bone strength factors by Lacovara et al. in 2014 that Dreadnoughtus had a mass of 59 tonnes is extremely excessive, the volumetric model indicating it was in the area of 34 tonnes.  

That models that replicate the probably volume of titanosaurs tends to produce less weighty results than do bone strength estimates probably stems from many titanosaurs being very strongly built relative to their size, perhaps in part as an adaptation to be able to battle the gigantic predatory dinosaurs of their time. 

Estimates that Patagotitan was 120 ft long are based in part on a neck length that is probably excessive -- the number of vertebrae is not known -- my skeleton is a little over 100 ft. Argentinosaurus could have been 120 ft. 

There are fragmentary remains from the Jurassic that suggest nontitanosaur sauropods matched the bulk of the later titanosaurs. 

Background -- 

I was the first paleontologist to begin to produce consistently crafted high fidelity dinosaur skeletal restorations, and deriving mass estimates from them starting in 1980. This led to the refutation of earlier mass estimates based on toy models. Pertinent references are as follows. 

Restoring maximum vertical browsing reach in sauropod dinosaurs. The Anatomical Record, 2017.

Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs. 
In Dinofest International Proceedings, 1997

Paleontological illustrations. Junior author T. Chase. In The Guild Handbook of Scientific
Illustration, 1989

The brachiosaur giants of the Morrison and Tendaguru, with a description of a new 
subgenus, Giraffatitan, and a comparison of the world's largest dinosaurs. Hunteria, 1988

The science and art of reconstructing the life appearance of dinosaurs and their relatives:
a rigorous how-to guide. In Dinosaurs Past and Present II, Natural History Museum of
Los Angeles County, 1987  

Baltimorean debunks dinosaur finds. B. Rensberger, Washington Post, May 11,
Associated Press, 1988