Giant theropods overview thread

[theropod]

Any estimate for the phalanx was probably invalidated beforehand, because the phalanx is probably way smaller than it appears at first sight from the published figures. The argument for that was rather convincing, whereas Snively gave no reason to presume he personally measured both phalanges.

[Grey]

I had read Spinodontosaurus observations. A good point would be that he contacts directly Snively. But perhaps he has the phalanx directly on hand ?

[Life]

I believe in the possibility of a T-rex larger than Sue.

[theropod]

I wouldn’t be surprised at all if we all did, it’s not the possibility that is up for debate, it’s the evidence among known specimens. In this case its, certainly not that likely that a researcher from Michigan would have personally measured an isolated phalanx from California and the phalanx of Sue (which is mounted and likely not that easily accessible) just for it to become a side note in an abstract, but if (unlikely as that may sound) he follows up with a detailed discussion of T. rex specimens, that’s a different matter. It rather seems like we can expect a detailed discussion of foot scaling though, because that’s the really interesting part in there.

Luckily there are many ways to test this using actual dinosaurs instead of humans and elephants, so hopefully we’ll get some data on how the feet scale in theropods and sauropods across their size range.
A simple test would be to see whether sue’s feet are twice the linear dimensions of a 2t-theropod, as they should be if mass scales with the square, or closer to isometry, at 1.6 times the dimensions.

[theropod]

So I’ve tried to verify Snively’s suggestions about foot scaling based on Hartman’s Allosaurus skeletals: scotthartman.deviantart.com/art/Allosaur-comparison-173333349
It fulfills the important criterium of the feet and all the other important stuff being preserved and their relative masses being easy to ascertain. One could argue that compared to "humans and elephants" this really doesn’t matter, but the two animals are also closely related.
EDIT: Oops, I’ve overlooked that DINO 2560 is in fact missing some pedal phalanges, so let’s hope it’s at least complete when taken together.

As for body mass, rostro-iliac lengths are 3.95m vs 3.45m, so DINO 2560 should be 50% more massive. Based on that, its feet should be 15% longer when following isometry, but 23% longer based on Snively (2016). Alternatively, rostro-iliac silhouette areas are 3.82m² vs 2.84m² making DINO 2560 56% more massive. 16% bigger feet based on isometry. 25% based on Snively.
As for the actual foot dimensions, I’m getting 16-18%. So Allosaurus seems to be closer to isometry, unless the skeletals are off.

It could be argued that these two are too close in size to filter out statistical noise, but certainly a theropod that is, say, 4 times the mass should solve that problem, shouldn’t it?
Using sue for comparison, its foot should be at least 95% bigger than DINO 2560’s based on Snively, 56% based on isometry. The real dimensions actually seem to be smaller than either, at just 40%. The same seems to apply within T. rex: Stan doesn’t have a complete foot for measurements, but as we all probably recall its measurements in that regard are fairly close to sue’s foot, despite being considerably smaller overall.
I’d usually say we could blame that on phylogenetic distance, but since the original suggestion bases on humans and elephants that doesn’t work, neither does it if we base it on the universal mechanical (and theoretically very convincing) principle that mass should scale with the second power of foot dimensions.

As for how I measured the feet, I started at the posteriormost phalanx and then measured consecutive proximodistal segments contributing to foot length, so the lengths I compared correspond to the maximum proximodistal length of the phalanges when straightened out. It’s true that that ignores the soft tissues, but wouldn’t we at least expect some osteological correlate if feet became proportionately that much bigger? Instead we are getting rather the opposite, feet scaling isometrically (as has been previously suggested for dinosaur feet by Grag Paul [DML] and Matt Wedel [SVPOW]) or even below isometry.

Does somebody want to check?

PS: I would have used Fran, but its pes is not complete. Currie & Carpenter estimate its third digit at "half a metre" though, add some centimetres for the more proximal attachments of the other digits and what you get doesn’t look like a disproportionately larger foot either.

[spartan]

Oct 1, 2016 17:16:11 GMT 5 Grey said:

No one has noticed this abstract talking about the potential size of the giant T. rex phalanx (and the Broome sauropod track) ?

FOOT STRESS SCALING CONSTRAINS ESTIMATES OF MASS FOR
ISOLATED, LARGE SAURISCHIAN DINOSAUR SPECIMENS
SNIVELY, Eric, University of Wisconsin - La Crosse, La Crosse, WI, United States of
America
Tracks and autopodial specimens of sauropod and theropod dinosaurs are
occasionally cited as representing exceptionally large individuals. These specimens
include sauropod tracks of the Broome Sandstone of Western Australia and Plagne in
Southern France, the biggest measuring 1.5 m or more in their largest linear dimension.
Among particularly large fossils of theropods, a Tyrannosaurus rex phalanx (UCMP
137538) is substantially larger than the homologous bone in the next largest specimen. A
common method of first approximating mass of large fossil animals is to cube ratios of
linear size between isolated elements and their homologs from more complete specimens,
and multiply the ratio by a mass estimate for the smaller individual. However, in humans
and elephants body mass scales linearly with surface area of the feet, which maintains
foot stress overall and/or stress from mass distribution between fore and hind limbs.
Squaring ratios of linear dimensions of foot fossils may be a better method of mass
extrapolation than cubing these dimensions.
The large Broome sauropod tracks have been precisely measurable, as clear surface
imprints with discrete anatomical features. Squaring ratios of their digital span to those of
other titanosauriform sauropods yields much lower estimate of body volume than cubing
the ratios, approaching but not exceeding current volumetric estimates of very large
sauropods based on body fossils. Squared-ratio and surface area estimates for the T. rex
phalanx suggest a mass between 11.5 and 14 tonnes, depending on conservative mass
estimates for other specimens.
Although foot areas correlate linearly and precisely with mass in humans, the
squared-ratio/stress-based methods must be part of a larger range of mass estimates
methods for morphologically diverse fossil taxa, especially based on isolated elements.

Where is that abstract from?

[Grey]

SVP 2016 abstract book

[Infinity Blade]

Regarding Tyrannosaurus' build: if we took it for what it actually was, then how would its bulk really compare with that of predators such as felids, canids, or ursids (the three examples Duane Nash brought up to compare Tyrannosaurus' build with)?

[theropod]

I’m not sure how meaningful that comparison will ever be, since theropod morphology is very different from carnivoran morphology. If you scale both to the same total length, the mammal is going to be much bigger, so based on comparing weight and length, mammals are bulkier. If you do the same for height, the reverse is likely going to be the case.
No doubt T. rex has a massive barrel-chest, but I’m not convinced by Nash’s reasoning that this is so unique or uniquely indicative of some particular behaviour (I think it is a consequence of the skull getting broader and needing more lateral support, actually). Look at pictures of bears. Actually, look at the picture of the lion he posted himself. These are all pretty broad-chested. Yes, you can see the tighs of a bear, but who’s to say that that’s because of the super-wide chest of T.rex, and not rather the wide hips of bears and the lack of soft tissues on the T. rex?
But I’m gonna have a closer look at a bear skeleton the next time I’m at the institute to see how its ribcage compares.

[Deleted]

Oct 26, 2016 3:16:16 GMT 5 theropod said:

On a related issue, regarding our recent discussion about skeletal maturity in tyrannosaurs, here’s a helpful passage from Horner & Padian that I had previously overlooked or forgotten about:

According to these estimates, a virtually fully grown T.
rex would have been between 15 and 18 years old. (How-
ever, as the femur of MOR 1152 shows, growth can drop
more precipitously than an incremental estimate suggests.)
We have not found in any sectioned T. rex tibia or femur
evidence of an outer acellular, nearly avascular layer similar
to the external fundamental system (EFS) (Cormack
1957), that indicates effective cessation of growth. (An
EFS has been identified in the ornithischian dinosaur
Maiasaura (Horner et al. 2000).) The absence of an EFS in
preserved specimens of T. rex could suggest that none of
the animals had stopped growing, although growth was
greatly slowing. Without an EFS, the near cessation of
growth seems the most practical indicator of full size.

Obviously an EFS has been identified by Erickson et al. in the same year in FMNH PR 2081, which was not studied by Horner & Padian, but the results seem to match up. "Skeletal maturity" in the sense of being "virtually fully grown" actually seems to fall together with the estimated age at reproductive maturity quite nicely (if I recall it correctly, you were right about your use of the term). However the state of skeletal maturity we see in Sue definitely goes well beyond that seen in other specimens.
ref: Horner, John R.; Padian, Kevin (2004): Age and growth dynamics of Tyrannosaurus rex. Proceedings of the Royal Society B Vol. 271 (1551) pp. 1875-1880.

So Tyrannosaurus had roughly concurrent sexual and skeletal maturity. That also makes Larson's ~11-11.2-meter-long figure for average adult Tyrannosaurus a lot more palatable. This also means that Stan, B-rex, and Bucky have already pretty much reached effective full size.

Well, that puts another nail in the coffin of the "use Sue to represent adult Tyrannosaurus rex specimens in general" logic.

[Ceratodromeus]

It's really not that big of a deal

[Deleted]

Nov 4, 2016 5:15:02 GMT 5 Ceratodromeus said:

It's really not that big of a deal

Every single roast to Nash's logic counts

[Grey]

David Hone in The Tyrannosaur Chronicles said some interesting points :



I ignored that some Zuchengtyrannus vertabrae was comparable to Sue's.

[Grey]

I got an interesting response from Eric Snively regarding the phalanx and Sue body mass.



It turns out that the skeptics were right! The abstract’s mass estimate was based on Longrich et al.’s (2010) measurement of 13 cm. When I examined the phalanx again to make a 3D model, I realized that it was slightly smaller than the same phalanx in Sue. I noted the correction on the poster, and will soon publish the updated estimates.

The difference is in what measurement you take. For the largest dimension (laying the specimen flat), I got exactly the same 13 cm measurement that Nick reported. However, that’s not the same measurement that Chris Brochu reported for Sue. If you measure the UCMP phalanx in Brochu’s way, you get 10.9 cm, compared with 11.1 for Sue. By my estimates, the UCMP specimen was about 9 tonnes, versus a bit more for Sue. (The UCMP phalanx is a bit broader anteriorly, but no bigger otherwise.) Brochu did a darned good job. You can really trust his scale bars.

You might be interested to hear about recent mass estimates for Sue. It was big; there’s no way around it. We have a paper coming out soon with an estimate of 9.2 +/- half a tonne, a range that about covers Scott Hartman’s earlier estimates and John Hutchinson et al.’s (2011) “lean” estimate. (The paper will also correct the SVP abstract’s estimates for the UCMP phalanx.) Our middle and upper estimates for Sue have realistically broad tails, following Heinrich Mallison’s study of adult crocodilians. The tail muscles are sensitive to the size of their most robust origins. The depth of the caudal centra dictates the width of m. caufofemoralis longus, and the centra are deeper in tyrannosaurs than other big theropods (or scaled-up crocs and lizards) of the same overall length. Other tail muscles scale to the size of the ilium and ischium, also big in tyrannosaurs. They had a lot of muscle mass where it counts.

[spartan]

"Tonnes" means metric tons?