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).
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 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 GDI of a slightly edited 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.
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:
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 '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 , Maraapunisaurus fragillimus silhouette by using Limaysaurus tessonei skeletal by as a base)
Here is the great SVPOW post on the matter:
And the original publication, discussing certain matters much further than I and SVPOW members did.
Congratulations are in order for fellow deviantartist 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
- Carpenter, Kenneth. 2006. Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus Cope, 1878. pp. 131-137 in J. Foster and S. G. Lucas (eds.), Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36.
- Carpenter, Kenneth. 2018. Maraapunisaurus fragillimus, n.g. (formerly Amphicoelias fragillimus), a basal rebbachisaurid from the Morrison Formation (Upper Jurassic) of Colorado. Geology of the Intermountain West 5:227–244.
- Cope, Edward D. 1878. A new species of Amphicoelias. American Naturalist12:563–565.
- Paul, Gregory S. 2016. The Princeton field guide to dinosaurs. Princeton, Princeton University Press. 360 pages.
- Taylor, Michael.p (2018) What if Amphicoelias fragillimus was a rebbachisaurid? Sauropod Vertebra Picture of the Week, 22 october 2018.
- Osborn, H.F; Mook C.G (1921) CAMARASA URUS, AMPHIC(ELIAS, AND OTHER SAUROPODS OF COPE. Memoirs of the American museum of Natural history. New series, volume 3, part lll.