Amphicoelias fragillimus redescribed
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Published: October 22, 2018
Just as predicted six years ago by Andcrea Cau in his blog, and four years ago by user :iconpalaeozoologist: , "Amphicoelias fragilimus" is now redescribed as a new rebbachisaurid taxon;  Maraapunisaurus fragillimus by no less than the renowned doctor in paleontology Kenneth Carpenter, the same sciencist that catapulted the 60 meters diplodocid version to fame in 2006.

The publication suggests that the morphological characters of AMNH 5777 show shared apomorphies (defining characters) with rebbachisauridae, and that thus should be considered to be part of said group. Going by this, Maraapunisaurus fragillimus would be the largest and oldest member known of this peculiar family; perhaps meaning that the clade could have originated in what today is north america in the upper Jurassic, archieving practically wordlwide distribution by the early cretaceous (exceptuating Asia and Antartica).

Carpenter2018-amphicoelias-fragillimus-is-maraapun by FranoysFragillimusrebbachisaurid by Franoys


To the left (shown above; original drawing by Cope (1878) labeled in Willson et al (2011). To the right, it compared with dorsal vertebrae of other rebbachisaurids (Rebbachisaurus grasbae and Histriasaurus boscarollii).

Maraapunisaurus fragillimus is known from a single partial neural arch of massive dimensions if we go by Cope's measurements (total elevation of neural arch preserved, 1500 mm; elevation of posterior zygapophyses, 585; transverse expanseof posterior zygapophyses, 190; vertical diameter of base of diapophysis, 390) . The older reconstruction by Carpenter of the complete vertebra was 2.7 m tall, and newer one is 2.4 m, just twice the height as the preserved dorsal vertebra of Limaysaurus tessonei (120 cm). This leaves us with an animal 2x the linear dimensions of Limaysaurus tessonei and 8x (2^3) it's mass asuming perfect isometry, although the distance between the neural canal and the postzygapophysis seems larger in proportion in Maraapunisaurus fragillimus than in Limaysaurus, meaning that this discrepancy could have been smaller and not a direct translation on how the vertebral heights correlate.

Asuming perfect isometry in reconstructed vertebral height, the length of Maraapunisaurus fragillimus would be between 28.6 and 30 m (going by the skeletal restorations of Limaysaurus by :iconpalaeozoologist: and Gregory S.Paul) and the mass between 56 and 61.6 metric tonnes ( mass of Limaysaurus is 7 t going by Greg Paul's estimate in the priceton field guide 2016, 7.7 t going by :iconspinoinwonderland: GDI of a slightly edited :iconpalaeozoologist: Limaysaurus restoration using my matlab script (specific gravities applied are 0.7 for the head, 0.6 for the neck, 0.9 for the torso, 1 for the tail and limbs).

Link to Limaysaurus GDI estimate.
i.imgur.com/Gkn1P7o.png

Diagram from Carpenter 2018, showing relative dimensions between the newer and the older version of his reconstruction of AMNH 5777. Old estimate involved a 2.7m high vertebra using a D.carnegii like body plan:

Amnh 5777 by Franoys

There is a posibility that the neck was slightly more elongated than what isometry predicts, as the neck length in several neosauropods scale with torso dimensions to the power of 1.35 as described by Parish (2006). This augments the posible linear dimensions up to 32 m, with mass increasing only slightly, as sauropod necks are not very massive in proportion and heavily pneumatized.

What happens with Amphicoelias as a whole, and with Amphicoelias altus specifically?


This would make it so M.fragillimus stops being closely related to Amphicoelias altus, and thus Amphicoelias altus survives as their own genus and species. Cope came to this conclussion in 1878 since A.altus was the only diplodocoid he had named, and while they still have the general resemblance expected in two diplodocoid taxa, M.fragillimus shares at least 2 apomorphies with all of rebbachisauridae, and other characters in common with some of them. Amphicoelias altus has been recovered within apatosaurinae according to Tschopp & Mateus 2017 analysis, and it's femoral dimensions (177 cm maximum length as indicated by Osborn & mook 1921) are close to that of B.louisae specimen CM 3018: with femoral length 178.5 cm and an estimated mass 22.4 tonnes by GDI analysis by myself using Scott Hartman's skeletal with a dorsal view by Gregory S.Paul ;Greg Paul's own estimate for this taxon is 18 tonnes) ,so despite the genus surviving, it now doesn't hold any record holder in terms of size.

Is M.fragilimus the largest sauropod dinosaur (and thus, largest terrestrial vertebrate) ever found according to this information?


Mazzeta et al 2004 proposed a mass of 73 t for Argentinosaurus huinculensis based on a referred femoral shaft using regression equations; an estimate close to a GDI done in :iconrandomdinos: 's Argentinosaurus reconstruction (in which I collaborated), that yielded between 71.4 and 75.4 metric tonnes depending on varying the ribcage width between plausible values. Patagotitan mayorum as described in Carballido 2017 could be slightly smaller than Maraapunisaurus fragillimus, with a convex hull +21% model of 55 t, though the maximum model (reconstructed with much more soft tissue than that applied to Limaysaurus mass estimates) yielded up to 77 tonnes.

Here is a comparison of M.fragilimus and A.huinculensis: (Argentinosaurus huinculensis by :iconrandomdinos:, Maraapunisaurus fragillimus silhouette by :iconrandomdinos: using Limaysaurus tessonei skeletal by :iconpalaeozoologist: as a base)
Fragilimuscomp by Franoys

Here is the great SVPOW post on the matter:

svpow.com/2018/10/21/what-if-a…

And the original publication, discussing certain matters much further than I and SVPOW members did.

www.utahgeology.org/publicatio…

Congratulations are in order for fellow deviantartist :iconpalaeozoologist: that has actually been acknowledged in the publication. 

Here is the original post that he made in this very same site:

Was Amphicoelias a rebbachisaur?Update (10/22/18): Dr. Ken Carpenter has recently published a new paper supporting the view below (and cites me favorably), but I would also be remiss to not recongize Dr. Andrea Cau for having thought up this idea 2 years before me. Sadly, he was not cited in Carpenter's paper. He and I both were unaware of Cau's work.
The last time I wrote about the size of Amphicoelias, I still used Diplodocus as a comparison. One of the comments that was made was that my size estimate was likely wrong, as Amphicoelias was probably a basal diplodocoid, not a diplodocid proper. After a little investigation, it turned out that two phylogenetic analyses have been published that included Amphicoelias, and both found Amphicoelias to be a basal diplodocoid. Whitlock (2011) was


References:

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Comments (44)
christina1969's avatar
"Maraapunisaurus fragillimus by no less than the renowned doctor in paleontology Kenneth Carpenter, the same sciencist that catapulted the 60 meters diplodocid version to fame in 2006."

Actually, Carpenter estimated it to be 58 meters long in 2006, not 60. It was Gregory S. Paul who estimated it between 40 and 60 meters in the 90's.
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The-Nerdinator's avatar
Apatosaurus louisae hasn't been reclassified into Brontosaurus, on what basis do you say that?
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Franoys's avatar
Franoys|Student Digital Artist
It's based on the abstracts of SVP 2016 (page 19) in which they speak about how it ends more related to Brontosaurus than to Apatosaurus in a newer anaylsis, though it is not published yet. Personally I wrote it almost unconciously. cdn.discordapp.com/attachments… .
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The-Nerdinator's avatar
Unpublished, you say? Explains why I couldn't find why half of DeviantArt just suddenly decided to use B. louisae.

In all honesty, I'm gonna stick with A. louisae until this paper gets published and other scientists weigh in on it. Remember, just because it seems like a good idea doesn't mean it's the best idea, and this abstract doesn't go into detail about why they made the change. So until they explain what anatomical basis they used to reclassify A. louisae, I'm not going to use it.
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anomally's avatar
The dream of a 100 ton plus sauropod is over:(. Maybe we are seeing the plateau of land based animal size limit, at around Argentinosaurus?
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MezoTheBugfield's avatar
Cough BYU 9024 Cough
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Almostthere99's avatar
8/10, not enough big.
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Almostthere99's avatar
yes, enough big.
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MezoTheBugfield's avatar
It traded it's size for a higher credibility of existing. Fair trade, i guess. Either way, if it does exist, It being a Rebbachiosaurid, and one that big at that is cool awesome epic
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Dinopithecus's avatar
Okay, so we still have a pretty big animal, but technically holds no records for largest sauropod (let alone largest animal) ever anymore. I can live with that. Not that I have an option lol.
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105697's avatar
Technically, its the tallest sauropod (and thus dinosaur) by hip (lower back?) height.
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105697's avatar
Shows right there on the chart. The lower back/hip height is 7 meters or so, which is taller than the lower back/hip height of any dinosaur.

Argentinosaurus still outweighs and outreaches it by a noticeable margin though.
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Dinopithecus's avatar
That's true (7 meters? Holy shit). I was only thinking about body mass when I wrote that.
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Majestic-Colossus's avatar
Yeah. 7 meters tall on the back. It dwarfs pretty much any sauropod when it comes to this. I can't wait for the French monster to be described, maybe it was even taller than that (it seems unlikely, but who knows?).
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TyrannosaurusPrime's avatar
"Mr. Cope, I don't feel so huge....."
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Saberrex's avatar
Saberrex|Hobbyist General Artist
Whoa!
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mark0731's avatar
"Mazzeta et al 2004 proposed a mass of 73.5 t for Argentinosaurus huinculensis..." Wasn't it 73 tonnes? I thought 73.5 tonnes is the newest GDI made by Henrique.

Reply  ·  
Franoys's avatar
Franoys|Student Digital Artist
It is just 73 t,indeed.
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rhe416's avatar
rhe416|Hobbyist Traditional Artist
The mystery is finally solved
Reply  ·  
PeteriDish's avatar
PeteriDish|Hobbyist General Artist
and this is exactly why I always take sensationalistic reports on sauropods of unusually large dimensions with a grain of salt. They never hold up to scrutiny.
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Spinosaurus14's avatar
This new information is like a kick in the balls for me, 30 m? Really? Why the hell did maraapunisaurus have to be related to the proportionally shortest mfs in the sauropod kingdom? It's as if the universe intentionally did it to annoy me, at this point amphicoelias might have also been a 2 m long dromaeosaurid with an exceptionally big spinal tumor... I am not arguing agaist science here, I'm just sharing my mild disappointment
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ForbiddenParadise64's avatar
A suitable name for the beast at least. Now the only current challenger to Argentinosaurus’ crown is BYU 9024, depending on where in the neck it is and whether allometry is at play (and if so, how much). Even if it’s just C11 (isometric scaling means it would be 5.64 timed as massive) and there’s significant allometry, it’s hard to get it under 50 tonnes due to the sheer proportions of it. 
Reply  ·  
ShinRedDear's avatar
ShinRedDear|Hobbyist Traditional Artist
Andrea Cau also suggested that conclusion, even before Palaeozoologist.
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