Size comparison scale

[Fragillimus335]

Aug 11, 2013 22:34:19 GMT 5 Grey said:

Theropod, my reasoning is simple and explained in Hartman words, Giganotosaurus represents the typical giant theropod that people basically expect, compared to the "weirder" because more specialized Spinosaurus or Tyrannosaurus. It is the largest and most massive of the most classically shaped predatory dinosaurs. Tyrannosaurs by comparison, despite the fame, are anatomically very strange, that was the subject of an article by Holtz. You agree or not but there's no substance to discuss at length about.

Fragillimus, you know my approach, I agree that there was certainly fluctuating sizes but I certainly won't guess that there were much larger specimens without hard basis, because we can apply, or not, this to any extinct genera, which has all the time brought to massive overestimates (except in some cases, like the behemoth Alamosaurus)

This Giganotosaurus (I guess this is the one based on the isolated dentary) is already fair enough, it is gigantic and it is based on material that we know to exist !

Yes of course, I'm talking numbers of ~10% or less in linear terms. In other words, I wouldn't be surprised if most giant theropod genera will eventually turn up specimens a meter or so longer than current remains. In just about every dinosaur species we have found, the first specimen has not been the largest.

[Grey]

With the numerous revisions in some cases, I'm not sure if "the first is not the largest" statement is totally true. But fair enough about the remaining part.

[coherentsheaf]

Aug 12, 2013 0:38:02 GMT 5 Grey said:

With the numerous revisions in some cases, I'm not sure if "the first is not the largest" statement is totally true. But fair enough about the remaining part.

I think there are several reasons why the first specimen described/ the sizes for genus when first published are often large for the genus. An important one is that if there are several known fossils at the time of description, the size of the largest will be the one that is kept in popular memory. Another one is that authors will exaggerate on first description.

But here are several examles where later discoveries turned out to be larger, e. g. Tyranosaurus.

[Grey]

Aug 12, 2013 0:47:47 GMT 5 coherentsheaf said:

Aug 12, 2013 0:38:02 GMT 5 Grey said:

With the numerous revisions in some cases, I'm not sure if "the first is not the largest" statement is totally true. But fair enough about the remaining part.

I think there are several reasons why the first specimen described/ the sizes for genus when first published are often large for the genus. An important one is that if there are several known fossils at the time of description, the size of the largest will be the one that is kept in popular memory. Another one is that authors will exaggerate on first description.

But here are several examles where later discoveries turned out to be larger, e. g. Tyranosaurus.

Certainly. Regarding Tyrannosaurus, that seems more complex. Prior to Sue discoveries, it was widely stated and repeated, not only in basic popular books, that T. rex reached sizes in excess of 12 m, even more than 14 m. The tail was reconstructed with more numerous vertebras. Then they brought Sue to light and at the same time understanding of their anatomy advanced. I recall, while believing that rex reached 14 m, I was surprised that "the largest of rexes" Sue was "only" 12 m...
Something similar has been seen with Allosaurus.

But your statement still stands. Now I recall a number of cases where the first specimen was also the larger even with additionnal specimens found. Don't recall exactly which cases but I'll try to find out again.

[blaze]

Tarbosaurus is one of those.

[Fragillimus335]

One of my favorites from an aesthetic standpoint, Stegosaurian diversity.

[theropod]

It's not that much whether the first is the largest specimen FOUND or not. It's generally speaking very likely that some random individual is pretty much average, and bigger as well as smaller ones existed. This is the case with all well-samples animals I'm aware of. It is probably everything but far fetched to assume of most Giant theropods there were specimens a good deal bigger than the few we have. Take Giganotosaurus carolinii, known from only two specimens--it is almost certain they don't represent anything even near the maximum size the species attained.
That doesn't mean we have to speculate on larger sizes, just be aware what those specimens that we have of most oligotypic taxa actually represent, and what they don't represent (single specimen=/=large specimen in two=/=large specimen in 30=/=large specimen in 1000).
In some rare cases one can presume a single individual may be above/below average, if it shows sign of being particularly old or young.

That usually overall sizes tend to get revised downwards is a completely different thing.

In the case at hand, T. rex*, it was erraneously reconstructed with 50+ caudals as in Allosaurus, leading to those lenght figures being spread, while newer findings showed this is exagerated. But you will also be able to note that the weight figures given were typically quite low (typically cited 6-7t), not higher, but rather lower than modern ones.
And of course it is often the case (eg. Pliosaurus funkei, Giganotosaurus carolinii, Tyrannosaurus rex) that already rough and uncertain sizes are additionally overhyped initially.

In all those cases, the size of the first is more exagerated than that of later specimens as we gain better insights (eg. the old 15m T. rex that is now obsolete), even tough it is usually smaller.

That being said, I think somewhat liberal size estimates (ie. liberal but scientific, not sensationalistic hype) will often come closer to the size a taxon could attain in many cases (when one or few specimens are known). Cautious ones will rather correspond to the lower bound or average sizes.

T. rex is a bad example here, but Carcharocles megalodon demonstrates the point. In a number of estimates (Gottfried et al., 1996) the more liberal figures (particularly the 17-18m, the latter based on more accurate size for the used GWS), albeit somewhat optimistic and unfounded for the specimens used, correspond far better to the size we can now say the species most likely reached.
With estimates of this kind it's likely to be the same for other animals too, especially those with far smaller samples.

*A somewhat peculiar case actually, since the T. rex holotype, albeit not the biggest, is clearly a large specimen only outsized by a handful in the comparatively high number of known individuals (I mean FMNH PR 2081, Peck's rex, [?]Celeste and likely the UCMP-toebone).

[Grey]

Globally agreed, although one thing to note : even if one or only two specimens are known, we can sometimes determine that one can be close to the maximum size, or at least a large one within its species. One example is P. funkei, only two members of its species are known but the larger displays signs of an advanced age and can be considered as a large individual (since pliosaurs grew their whole life). This is also likely the case of the larger P. macromerus specimem. Even if only one specimen of the species is known, if its age is determined, we can expect if it is close of the upper range of its species or not. About Giganotosaurus, I don't want throw some cold water on it but I would simply recall Hartman, the dentary could represent a larger specimen than the holotype but could also represent a bigger-jawed individual not so bigger than the holotype. That does not reject that larger individuals other than this one may have existed, that simply shows that bigger Giganotosaurus could exist, but not obligatory much bigger than the size estimated for the dentary owner.

Once again, the purpose of this is not to throw cold water on optimistic claims but to be cautious with the "the first is necessary not a large one". Things are never that simple.

Megalodon's case is much more difficult than in dinosaurs known by skeletons (worldwide distribution, relative uncertainties between methods of estimates, possible regional size differences, temporal size differences, juveniles (m/f), teeth positions...).

[Grey]

By paleo-artist Alberto Gennari.


One question : nobody is surpised how little documentation exists about the size of Spinosaurus teeth despite they are the only dinosaurians teeth rivaling in size with Tyrannosaurus teeth (10 inches or more vs 12 inches) ? One of the only mention of this statement was made by Tom Holtz for example.

[theropod]

^Well, for once, that's just lenght. T. rex' teeth are undeniably the most massive ones recorded for a Theropod.
Also T. rex teeth are only the longest in total lenght (and I doubt T. rex is rivaled by Spinosaurus here, besides, we haven't found complete teeth in MNSN V4047), due to the long root. There are several other teeth (eg. MUCPv-Ch1, CPT-1980) with similar crown heights to large T. rex teeth tough.

That Spinosaurus skull seems a bit undersized, if that's a 99cm rostrum the T. rex exceeds 1,5m.

Another thing, according to the Theropod Database Giganotosaurus' Ilium is noticeably longer than the femur:

(MUCPv-Ch1) (12.2 m, 5 tons) (skull- ~1.8 m) premaxilla, maxilla, maxillary teeth (74, 97 mm), nasal, lacrimal, postorbital, quadrates (410 mm), braincase, ectopterygoid, pterygoid, anterior dentary, dentary tooth, tooth (>82x45x18 mm), tooth (102x39.5x22 mm), tooth (88x33.5x20 mm), axis, most postaxial cervical vertebrae, most dorsal vertebrae, dorsal ribs, first caudal vertebra, caudal vertebrae 7-21, two distal caudal vertebrae, eight chevrons, scapula (727 mm), coracoid, ilium (1.54 m), pubes (1.11 m), ischia (1.2 m), femora (1.43 m), tibia (1.12 m), fibula (835 mm), metatarsi, pedal elements

Strangely in Hartman's skeletal the ilium seems atrophied, in fact none of the hip bones seem longer than the femur, this one the least. Paul seems to show a bigger one, but mainly dorsoventrally.

[Grey]

You should discuss this with Scott once he gives signs. Since a few weeks he does not show activity (on FB). He's probably in holidays.
I don't know Gennari's basis for the skull, I guess this is Hartman's work. I will ask him.

[Dakotaraptor]

I checked (old) Gregory Paul's Giganotosaurus and the ilium isn't longer than 1.3 m assuming if the femur is 143 cm.

Edit: ... and new one has also shorter ilium than femoral. 

[blaze]

I'll have caution with those figures by Mortimer, they seem to be taken from the skeletal in Coria & Salgado (1995), MisteryMeat made that same question on Hartman's deviantart, I responded months later when I found Coria & Salgado (1995), that no detailed illustration or even description of the ilium were present in the paper, much less any measurements, but that in the skeletal they had, the ilium indeed appeared to be 154cm long but it looked nothing like what Hartman has illustrated or what is present in Mapusaurus and Acrocanthosaurus, I noted that the skeletal in the paper is not very good overall and that maybe it was drawn/reconstructed too long.

Hartman later responded this:

Bingo. I had some measurements and lots of photos, so I feel pretty good about the proportions here (and not so good about the original paper's proportions).

The measurements and photos were likely provided by the ROM since they had the mounted skeleton last year and they commissioned the skeletal for the exhibition.

[theropod]

So the original skeleton didn't just withhold most of the known bones but also reconstruct/misscale parts of what was shown?

Hartman already told me he had used unpublished material for the reconstruction. I just whish it was documented.
My suggestion would be "Hartman, Scott; Osteology and reconstructed skeletal structure in the mid-Cretaceous carcharodontosaur Giganotosaurus carolinii (Coria&Salgado, 1995).", best in PLOS, APP or Palaeo-electronica, and preferably 2013

[blaze]

It seems likely, just look at it, it even appears to have bunny arms, it isn't a very good skeletal, and god how I hate nature papers, they always squeeze them into two pages and call it a day.