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Amphicoelias fragillimus
Topic Started: Jan 7 2012, 11:29 PM (20,977 Views)
Spinodontosaurus
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Herbivore
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Temporarily becoming a necromancer here, but some of you may remember in January that Zach Armstrong more rigorously estimated the size of Amphicoelias fragillimus based on estimated vertebral dimensions other than height. Here is the article, and at an estimated 78 tonnes, it's big, but a far cry from the 200 tone monstrosity it is sometimes claimed to be. (And although he doesn't list it as an estimate, the estimated centrum length would suggest a total length of around 45 meters)

Well, he's at it again, only this time reconstructing it as a mega-rebbachisaur reflecting it's possible status as a basal diplodocoid. At 'only' 28.6 meters long and 51 - 53 tonnes, the reconstruction is considerably smaller than even his Diplodocus-based estimate. And with feet estimated at 144 cm, it suddenly makes those 150 cm fossilised footprints seem much less gigantic too.

For comparison, Armstrong estimates the largest Alamosaurus at 74 tonnes, and Argentinosaurus at 64 tonnes.


I think the original article was posted here in another thread, but I really don't want to revive that one (the first few pages are painful to read... to much fanboyism and overly enthusiastic estimates)... so here, I guess.
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Drift
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The animal is still impressive imo if it's weights are far off from what was once expected to be its max volume,being the longest vertebrae still counts for something imo
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Spinodontosaurus
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Yeah, and even a 50 - 80 tonne sauropod is still huge, among the largest.
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Drift
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Exactly my thought on the matter, just because in actuality it doesn't break any land organisms record for weight it could distribute.Doesn't mean it wasn't impressive, seeing an animal as long as a city street slowly pacing towards vegetation would be whelming.
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7574
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thank 60 m sauropod is overstatent,ent
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ArachnidKid
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7574
May 16 2014, 05:52 PM
thank 60 m sauropod is overstatent,ent
in your opinion,maybe
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Thalassophoneus
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When I heard about it for first time I couldn't believe that such a huge dinosaur existed.
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Thalassophoneus
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26/5/2015.
Back at the first post I ever made in the Forum!
Edited by Thalassophoneus, May 27 2015, 03:14 AM.
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SpinoInWonderland
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Amphicoelias isn't a basal diplodocoid or a rebbachisaurid-like form anymore. It's once more a flagellidaudatan, within Diplodocidae, but now it's considered more basal than both Apatosaurus and Diplodocus.

Quote:
 
Amphicoelias altus AMNH 5764

The holotype of Amphicoelias altus is found in the same position within Apatosaurinae in both analyses. However, this finding is in contrast to the positions found by Rauhut et al. (2005), Whitlock (2011a), Mannion et al. (2012) and Tschopp & Mateus (2013b), who recovered it more basal than Dicraeosauridae, and even outside Diplodocimorpha in most analyses (Rauhut et al., 2005; Whitlock, 2011a; Mannion et al., 2012).

Three ambiguous autapomorphies were considered valid for the holotype of Amphicoelias altus (256-1, 275-0, 427-0; Table S111), but are all shared with some diplodocine specimens. Nearly horizontal dorsal postzygapophyses (275-0) are widespread among sauropods, and thus are probably not a meaningful autapomorphy. Furthermore, the orientation of the posterior dorsal postzygapophyses in Amphicoelias contrasts with the state in all other apatosaurines. The possession of a gracile femur (427-0) contributes in part to the “stove-pipe” shape of this element, most often used as the best way to distinguish Amphicoelias from other sauropods (e.g., Wilson & Smith, 1996). In fact, this is the autapomorphy shared with the fewest other taxa in our dataset (Shunosaurus lii, Cetiosauriscus stewartii, Ligabuesaurus leanzai and Diplodocus USNM 10865). Amphicoelias shares the diplodocid synapomorphies of short posterior dorsal transverse processes (263-0), and the presence of a lateral bulge on the femur (428-1), neither of which are present in any other sampled diplodocoid sauropod. A diplodocid affiliation is thus probable. This is also supported by constrained searches, excluding Amphicoelias altus from Apatosaurinae, or forcing it into a close relationships with Supersaurus vivianae, which was found to be the closest fit in a preliminary morphological disparity analysis.

Inhibiting a grouping of Amphicoelias with Apatosaurinae in the equally weighted analysis results in a tree two steps longer than the original (0.1% length increase). Amphicoelias is here found as sister-taxon to Galeamopus hayi within Diplodocinae, but no synapomorphy supports this grouping. When doing the same with implied weighting, tree length increases by 0.01% to 194.24251. Here, Amphicoelias moves into a position basal to Apatosaurinae + Diplodocinae, but still within Diplodocidae. A close relationship with Supersaurus appears substantially less probable, increasing tree length by 0.15% (ew) or 0.11% (iw).

Mean pairwise dissimilarity supports diplodocine affinities of Amphicoelias altus slightly more than a referral to Apatosaurinae: principal coordinates 1 and 2 recover A. altus slightly closer to the diplodocine cluster than to the apatosaurine specimens (Fig. 112). Given the minimal length increase in the constrained analysis with implied weights, the absence of apatosaurine synapomorphies in A. altus, and the fact that previous analyses agreed in a more basal position for this taxon within Diplodocoidea, a position outside Apatosaurinae + Diplodocinae is herein interpreted as more plausible than the apatosaurine affinities recovered in the most parsimonious trees.

Tschopp, 2015, "A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda)"
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What an impressive beast.
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Thalassophoneus
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SpinoInWonderland
May 27 2015, 05:48 PM
Amphicoelias isn't a basal diplodocoid or a rebbachisaurid-like form anymore. It's once more a flagellidaudatan, within Diplodocidae, but now it's considered more basal than both Apatosaurus and Diplodocus.

Quote:
 
Amphicoelias altus AMNH 5764

The holotype of Amphicoelias altus is found in the same position within Apatosaurinae in both analyses. However, this finding is in contrast to the positions found by Rauhut et al. (2005), Whitlock (2011a), Mannion et al. (2012) and Tschopp & Mateus (2013b), who recovered it more basal than Dicraeosauridae, and even outside Diplodocimorpha in most analyses (Rauhut et al., 2005; Whitlock, 2011a; Mannion et al., 2012).

Three ambiguous autapomorphies were considered valid for the holotype of Amphicoelias altus (256-1, 275-0, 427-0; Table S111), but are all shared with some diplodocine specimens. Nearly horizontal dorsal postzygapophyses (275-0) are widespread among sauropods, and thus are probably not a meaningful autapomorphy. Furthermore, the orientation of the posterior dorsal postzygapophyses in Amphicoelias contrasts with the state in all other apatosaurines. The possession of a gracile femur (427-0) contributes in part to the “stove-pipe” shape of this element, most often used as the best way to distinguish Amphicoelias from other sauropods (e.g., Wilson & Smith, 1996). In fact, this is the autapomorphy shared with the fewest other taxa in our dataset (Shunosaurus lii, Cetiosauriscus stewartii, Ligabuesaurus leanzai and Diplodocus USNM 10865). Amphicoelias shares the diplodocid synapomorphies of short posterior dorsal transverse processes (263-0), and the presence of a lateral bulge on the femur (428-1), neither of which are present in any other sampled diplodocoid sauropod. A diplodocid affiliation is thus probable. This is also supported by constrained searches, excluding Amphicoelias altus from Apatosaurinae, or forcing it into a close relationships with Supersaurus vivianae, which was found to be the closest fit in a preliminary morphological disparity analysis.

Inhibiting a grouping of Amphicoelias with Apatosaurinae in the equally weighted analysis results in a tree two steps longer than the original (0.1% length increase). Amphicoelias is here found as sister-taxon to Galeamopus hayi within Diplodocinae, but no synapomorphy supports this grouping. When doing the same with implied weighting, tree length increases by 0.01% to 194.24251. Here, Amphicoelias moves into a position basal to Apatosaurinae + Diplodocinae, but still within Diplodocidae. A close relationship with Supersaurus appears substantially less probable, increasing tree length by 0.15% (ew) or 0.11% (iw).

Mean pairwise dissimilarity supports diplodocine affinities of Amphicoelias altus slightly more than a referral to Apatosaurinae: principal coordinates 1 and 2 recover A. altus slightly closer to the diplodocine cluster than to the apatosaurine specimens (Fig. 112). Given the minimal length increase in the constrained analysis with implied weights, the absence of apatosaurine synapomorphies in A. altus, and the fact that previous analyses agreed in a more basal position for this taxon within Diplodocoidea, a position outside Apatosaurinae + Diplodocinae is herein interpreted as more plausible than the apatosaurine affinities recovered in the most parsimonious trees.

Tschopp, 2015, "A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda)"
Flagellidaudatan? What is this?
In any case I insist that Amphicoelias was a diplodocid. Almost all the specialists agree.
Edited by Thalassophoneus, May 28 2015, 02:47 AM.
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Jinfengopteryx
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SPINO/BROLY, YOU'RE BACK!!!!!!

On topic:
@KaizerGoji
Flagellicaudata = Diplodocidae + Dicraeosauridae
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Thalassophoneus
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Jinfengopteryx
May 28 2015, 03:17 AM
SPINO/BROLY, YOU'RE BACK!!!!!!

On topic:
@KaizerGoji
Flagellicaudata = Diplodocidae + Dicraeosauridae
I did have the sense this guy was gone for months.

On topic: So it's like a cross of Diplodocidae and Dicraeosauridae?
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Spinodontosaurus
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No, it's not a "cross" between them. Flagellicaudata contains both Diplodocidae and Dicraeosauridae.

I suppose this graph on Wikipedia might be more useful in explaining it.
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Lightning
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It's hard to read through 6 pages, so will someone please tell me what's the most recent weight estimate for amphicoelias?
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