Tyrannosaurus Leg Musculature Literature

[Adrian Boeye]

This is largely a shot in the dark, but is there any material on the sizes and dimensions individual muscles of the leg of Tyrannosaurus? I tried to look at the data from Sellers et al. 2017 but unfortunately I am not fluent in the source code of gaitsym (although if someone knows the material and how to read said source code, having that information shared would be greatly appreciated). I am largely interested in this to try and calculate individual PCSAs and see how varying fiber lengths and degrees of pennation can change force generation (if it is of interest, I am also happy to share whatever I come across that may be somewhat interesting).

Best,

Adrian

[Jura]

Carrano and Hutchinson 2002 are a good reference here. They go over all the individual hindlimb musculature based on scarring patterns on the bone, and inferred homology based on bird and crocodylian dissections.

https://onlinelibrary.wiley.com/doi/abs/10.1002/jmor.10018

Unrelated, but also kinda related, Burch 2017 (myology of Majungasaurus forelimb) offers another useful insight into inferring muscle mass based on homologous landmarks.

https://onlinelibrary.wiley.com/doi/full/10.1111/joa.12660

Cheers,

Jason

[Adrian Boeye]

This is indeed a good reference! I am largely able to work out the length of individual muscles now (although radius, volume, and PCSA will take some time). 

Also quite interesting, I will be giving this a more thorough read over it deserves but it does seem reasonably intuitive. Thank you again for sharing both of these, it makes the process significantly more do-able.

Best,

Adrian

[Martin Bäker]

Late to the part,y but there is also a huge table with muscle and segment in our 2009-paper

Constraint-Based Exclusion of Limb Poses for
Reconstructing Theropod Dinosaur Locomotion
Authors: Gatesy, Stephen M., Bäker, Martin, and Hutchinson, John R.

[Adrian Boeye]

Hello,

Apologies for not responding as quickly as I should have but I am looking over the publication now and this also looks quite useful,  importantly as well having individual segment masses on hand should be a very useful cross reference.

I do have a follow up question that is not entirely related to muscle mass, but instead COM. Looking at figure 5 in your publication I see what looks like the centers of mass depicted as bars next to mid-stance poses. To confirm exact positioning- poses 1, 3, 4, and 5 (if using the COM that allows for running) all have the COM positioned at various parts of the proximal phalanx, while pose 2 has a COM at the distal end of the second phalanx? Apologies for such a specific question, however the positioning of COM above the foot has become a point of interest and I want to ensure I get the detail right.

Best,

Adrian

[Martin Bäker]

Sorry, also late in answering.

We did vary the COM for all poses. So what you see in 5c is the GRF you get as a function of hip height for all three positions of the COM.

The colored asterisks in 5d mark which joint is the one that determines the limit (ie, has the max muscle force, IIRC),  the COM postion is marked by the vertical bar. We should probably have put markers for poses 1-4 in 5C as well but the plot would have been cluttered.

So pose 1 and 2 would work with the COm in the yellow and blue position, but not in the red one.

Concerning the COM, there is another paper by John Hutchinson where he looks at the plausible variation of T rex mass, size, COM position etc.: A Computational Analysis of Limb and Body Dimensions in Tyrannosaurus rex with Implications for Locomotion, Ontogeny, and Growth

but I was not involved in that study.

Hope this helps

Martin

PS (if you include me directly in any answer, I'll probably react faster.)

[Adrian Boeye]

Hello,

that is quite alright, I imagine we are both fairly busy. That would make sense, I could imagine trying to use the different hip heights with the same COM could prove a bit awkward. The challenge also of including the markers is quite understandable as well, I could imagine it would affect readability without really adding all that much. What I am finding really interesting about all these is (at least to my untrained eye) how the stance can shift to better adjust for a different COM and just how the general articulation is pretty strongly maintained in the foot even if the exact degrees of crouch vs uprightness vary significantly, all the while facilitating a GRF that crosses that 1.5 threshold. Looking at the 2011 paper, it looks like COM is pitched usually beyond 0.5 M, so around the yellow and blue positions which holds some interesting implications for stance, although as the results in 5c suggest, probably results in a reduced GRF. This is really interesting, and has been incredibly helpful (I would not have known about the shifted COM for the figures and would have taken more time on asterisks, etc), getting clarification from original authors as well is again super useful but also just an awesome experience. 

Best,

Adrian

PS, I think I included you in the answer? I am not sure though, google groups has often been uncooperative for me so I hope to have it figured out at some point

[Martin Bäker]

"That would make sense, I could imagine trying to use the different hip heights with the same COM could prove a bit awkward."

Might be misunderstanding what you mean, but we did use all configurations (i.e. al hip heights) will all COM positions at least for all configurations that were not excluded by other reasons. Of couse, COM has to be above the midfoot, so some config/COM combinatons were not allowed.

But yes, the stance can shift slightly to accomodate a shift in the COM.

When comparing Trex to the other species we looked at, I think the real message is not that Trex could accomodate different conditions, but that the Trex mid-stance is actually extremely constrained and only a very small range of poses is actually possible, different from smaller critters that can achieve a GRF of 1.5 with a large variety of stances. Especially when considering that Trex would not run over perfectly even ground, I think this shows that fast running is at least a lot more difficult for Trex than smaller Theropods.

OTOH, there is some aspect that AFAIK noone has looked at so far: Trex has a heavy tail. In all calculations (ours and also others I have seen), the whole body is assumed to be rigid. However, if the tail were to move upwards and downwards in concert with the leg movement, one could reduce the neede GRF at midstance a bit (a similar thing is happening with ahopping kangaroo). I remember doing some back-of-the envelope estimates showing that this might increase running speeds by 10-20%, however, I do not know if the tail muscles woud actually allow this.

[Gregory Paul]

Folks still referring to all eutyrannosaur specimens from the TT-zone as Trex. This when it is screamingly obvious that there are multiple species even among the adults. This is like putting all big Panthera in leo, and then doing detailed biomechanics on skeletons from Africa, Eurasia and N Amer as though they are one species. Instead people should be testing species diversity and its relationship to biomechanics and vice-versa by examining them as distinct species. 

Probably a waste of time though. It is obviously not possible to restore the biomechanics of extinct exotic creatures in detail. It's an absurd notion. Starting with the skeletons being distorted. The pelvis of Sue is smeared fore and aft. The corresponding right and left ribs have very different curvatures, overlay the photos in the Brochu description. The skull was run over by a Mac truck off of I-80. Stan was never described and who knows what is happening to that. Scotty which actually is a robust one small incisor T rex with the Mickey Mouse postorbital bosses was found in bits and pieces. And so on with the assorted specimens. We can get fairly decent overall body masses from the specimens and that is about it. We cannot get even get a solid value on the % of total mass made up of locomotary muscles much less individual muscles. All estimates of COG are high +/- approximations due in part to the impossiblity of accurately restoring soft tissue air-sacs -- were those limited to the chest area as in ratites, or expand all the way to the pubis as in most flying birds? We shall never know. At most varying possiblities can be examined and from that estimated a broad range of possible results, which is not particularly valuable. 

All this effort to try to restore the detailed anatomy of beasts extinct tens of millions of years is fun and seems productive and makes for big career enhancing technical papers (rather like the ones calculating early whales as big as blues and early ichthyosaurs as big as sperm whales), but it is like Alice trying to keep up with the Red Queen who was going nowhere. There are limitations to what science can do, but people will keep ignoring that. 

GSPaul 

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[Adrian Boeye]

Hello,

Apologies if the writing was confusing, I at least intended to remark about the clutter of including all the markers on the figure. 

That generally is the takeaway I also got from the study. While I did find it interesting to see what could be supported, there is far more that could not be supported. In figure 2 the visual is pretty incredible about just how few mid-stances actually support GRF of 1.5. I want to say it was in a talk by Dr. Hutchinson where he discussed that out of thousands of potential poses that were geometrically possible, only a 100 something could support a GRF of 1.5. You also raise an interesting point about the ground itself- the ground is almost never a perfect surface for running, especially in nature where open hard surfaces with out obstructions are limited compared to today. For sure though, fast running for a T. rex is definitely much more challenging than getting the same results for smaller theropods (which to be fair, given a lot of recent work seem to be very good runners). 

That is quite interesting- I know there has been some stuff that has been discussed with the tail (a comment on the Sellers et al. 2017 paper, an abstract from SVP about kinetic energy being stored in the spinal column and tail also by sellers and bates I want to say, another SVP abstract mentioning tail stuff, and  Bishop et al. 2021 come to mind) but none have tested it specifically for T. rex, and even the studies that did look at the motion of the tail have some limitations since most of the animals they looked at did not have such a hypertrophied set of tail musculature. Out of curiosity, if you still have some of the data/inputs you used and of course if you wanted to, would you be able to send some of the information? I can respond separately with my email address if groups is being uncooperative. I also do not know if the musculature could support that change, but it is definitely worth looking at since some more recent publications have indicated enormous caudal musculature, to a point where the degree of hypertrophy is almost comical. There is a good shot at figuring out a set of realistic PCSAs, looking at force generation etc and seeing what may or may not be plausible. Either way, I think it indicates more and more that new models will have to become increasingly dynamic.

Best,

Adrian

[Tim Williams]

Gregory Paul wrote:

> All this effort to try to restore the detailed anatomy of beasts extinct tens of millions of years is fun and seems productive and makes for
> big career enhancing technical papers

It also makes for some high-profile quasi-technical books as well.  I have a few such books on my bookshelf, like "Dinosaurs of the Air".

;-)

[Michael Habib]

> On Oct 20, 2024, at 5:14 AM, 'Gregory Paul' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:
>
> All estimates of COG are high +/- approximations due in part to the impossiblity of accurately restoring soft tissue air-sacs -- were those limited to the chest area as in ratites, or expand all the way to the pubis as in most flying birds? We shall never know. At most varying possiblities can be examined and from that estimated a broad range of possible results, which is not particularly valuable.

It can be quite valuable in the correct context. A broad range of possible results still excludes some options. Coming at the same problem from multiple different approaches can narrow in the potential range of answers still further. The answer will always be rough, but can still yield a repeatable, quantitative basis for comparison between animals. In such a comparative context, the exact values are not really the point, making comparative conclusions are more robust to the uncertainties.

Often the most valuable result of modeling extinct species is that it allows us to test and refine our predictions over a wider range of anatomy and size than with extant species, alone. If we think we have an idea of how running relates to COM, and we think we are modeling it well, but our model predicts that you cannot have a 6 ton biped… well, then we know we’re wrong, because tyrannosaurs have something to say about that.

> All this effort to try to restore the detailed anatomy of beasts extinct tens of millions of years is fun and seems productive and makes for big career enhancing technical papers (rather like the ones calculating early whales as big as blues and early ichthyosaurs as big as sperm whales), but it is like Alice trying to keep up with the Red Queen who was going nowhere. There are limitations to what science can do, but people will keep ignoring that.

If only technical papers in paleontology and/or biomechanics were that career enhancing. That said, you’re not wrong that there’s pressure to exaggerate sizes of specimens.

Cheers,

—Mike

[Martin Bäker]

Sorry, I do not have the input data or the code readily available anymore. I could probably dig out the (very ugly) C++-code from some old hard disk, but it is not easy to parse IIRC.

I also think that this would require to look at the tail/back musculature as well because an up-down-bobbing of the tail would involve other muscles than the leg muscles. The simple calculation I did back then was, IIRC, just assuming that the tail could move in whatever way and to estimate from its mass how much a correctly timed movement might flatten GRF curve that is sine-shaped over time. In any case, I totally agree that models should become more dynamic.

[Adrian Boeye]

Hello,

That is quite alright, even getting to know about some of the testing is already quite helpful.

Re: tail/back musculature. There is good data for some of the hypaxial musculature of the tail, but information for the epaxial musculature is lacking, and AFAIK while there might be some material on exact muscle placement, not much has been done on exact sizes of individual muscles. Certainly a new area for study.

Best,

Adrian

[Martin Bäker]

Of course any calculation like the one we did back does not look at the whole range of body sizes/shapes possible for a species (or several, if your split of Trex is correct). But the same is true for experiments on living animals as well - when an ostrich is studied in a lab, it is one animal, not the species we look at. (And I freely admit that I found it a bit comical to sometimes repeat my calculatons because one of my co-authors said that it might be more realistic to increase the femur length by a few millimeters...)

Nevertheless, we use the data we have to create a "typical" member of the species and look at its mechanics. Difference like the one we found between Trex and lighter theropods were large and surely tell us something about how this species did (not) move.

Furthermore, we can look at posisble ranges like Hutchinson did in   the paper I cited earlier. We could (and should) create different sample individuals from the morphometric space of possibilities and study how they differ and what they have in common. This will tell us something about the species for sure. There will always be uncertainties, but if we quantify them, we can still learn a lot about what was posisble and what was not.

[DrgnmstrZ111]

Hey, I’m kinda new to the world of paleontology, could i get a simplified version or explanation of this info please?

Sent from my iPhone

On Oct 21, 2024, at 2:13 AM, 'Martin Bäker' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:



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[Adrian Boeye]

Hello,

Apologies for this being such a slow response. Summarizing all the studies referenced here in one go is a bit difficult; but the easiest gist of it is that while a T. rex was extremely muscular, and in turn those muscles could produce absolutely enormous contractile force, there is also just a lot of T. rex to move. As such, even with all that force generating capability, some fundamental biological limits incurred by being so big would result in fairly significant limitations. I would recommend looking at the studies discussed in the posts, they are genuinely phenomenal although a fair warning that these are pretty technical papers. A good starting point for a lot of the stuff that is being discussed can be found here https://youtu.be/TxYireDupvo?si=vanv86gQ1U0TWIv- it is an excellent talk by Dr. John Hutchinson who has been doing decades of work related to T. rex and is one of the best out there. Hoping this helps a bit, but if you need something more specific, just send a message and some of the other folks here or myself would be more than happy to discuss further!

Best,

Adrian

[Richard W. Travsky]

 

Speaking from a lay being’s perspective, most of what I’ve read or observed in skeletal illustrations is that such tails look too stiff to have as much range of motion up and down as sideways, or perhaps up and down mostly towards the end of the tail. Was that aspect modeled, that is, heavy tail and side to side motion effect on speed?

 

As a side question, could there be a contribution to speed (or even just walking) from those diminished arms? In human running, swinging arms have a role affecting energy expenditure and breathing in both walking and running

[Jura]

The "stiffness" of tetanuran tails has been exaggerated in the literature and especially so in paleo-art. Even the reinforced, "stiff" tails of dromaeosaurs are still capable of holding a sinuous shape (notably, see Norell and Makovicky 1999). Tail stiffening via zygaphophyses appears to affect dorsoventral motion more than lateral motion (see Organ 2006), so it should make it easier to hold the tail up, whereas the animal could likely still swing and curl its tail, though the degree of curling would vary by species (think more iguana than chameleon). In fact, I would imagine a fleshed out tail in a living tyrannosaur would probably behave no different from the less stiffened tail of a ceratosaur in normal day to day activities.

As for arm contributions to speed, I would be doubtful for even the most well-endowed maniraptoran. Birds and bipedal lizards typically lock the arms close to the side of the body when walking/trotting along. Sauropsids are largely considered to be "rear wheel drive" animals that use their forelimbs more to catch their bodies as they move along (Hotton 1994). This is contrast to mammals, which seem to have opted for a more front-loaded form of movement. That may explain in part why we swing our arms when we walk (following the same asymmetric pattern as a quadruped). Humans also evolved a radically different (read: worst) way of walking bipedally, so a little counterbalance via arm swing seems necessary for us, as opposed to birds, kangaroos, or bipedal lizards.

Cheers,

Jason

Refs:

Hotton III, N., 1994. Why dinosaurs were not mammals and vice versa. The Paleontological Society Special Publications, 7, pp.39-60.

Norell, M., Makovicky, P.J., Akademi, M.S.U. and Mongolian-American Museum Paleontological Project, 1999. Important features of the dromaeosaurid skeleton. 2, Information from newly collected specimens of Velociraptor mongoliensis. American Museum novitates; no. 3282.

Organ, C.L., 2006. Biomechanics of ossified tendons in ornithopod dinosaurs. Paleobiology, 32(4), pp.652-665.

[Gregory Paul]

The group in which the tail really was stiff were the hadrosauroids with the ossified criss-cross rhomboid. And I suspect the dromaeosaur tail was not particularly flexible. 

GSPaul 

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