Giant theropods overview thread

[theropod]

just wanted to let you know, I've made an alternate giganotosaurus skull that I'll post tomorrow, and et me tell you, you wouldn't believe how much doing some changes on the reconstructed parts of the maxilla and the nasals can change the shape and lenght of a skull (the referred specimen ends up at around 15cm longer than the version you can see here)

[theropod]

here you go.

I only changed the maxilla and adjusted the nasals, everything else is identical in the two reconstructions. The lenght changed considerably, much more than I would have expected.
Decide for yourself which oen you like better, imo these two are good bounds but i cannot decide which oen I like better.

[creature386]

To make them turn up, write "http" instead of "https".

[theropod]

oh, thanks, I hadn't tought the forum had problems with secure connections for images. they just have that url when I copy them, and elsewhere it worked, so I never bothered changing them...

[Grey]

Mar 2, 2013 3:46:20 GMT 5 theropod said:

This model is based on the holotypic material and Acrocanthosaurus, it has little to do with typical carnosaurs or allosaurs, the size bases on the quadrate lenght (the scalebars in the description which I could send to you are unfortunately wrong). Everything you see there is the correct size, at best the whole thing might have been more elongated in places like the front of the maxilla, nasals and posterior maxillary main body (I'll see what I can do, several versions have never done me any harm).
Hartman didn't make a skull reconstruction, did he? He included a rough outline in his skeletal, and it isn't all too different from mine. Basing something on it would be pointless, after all he doesn't have more material either. He might have done a bit of said changes, but not much, after all the total lenght of the skull isn't too different. The skull shape, especially the maxilla of giganotosaurus makes it seem even deeper than it is, but there are definitely considerable differences between it and Carcharodontosaurus.

T. rex bases on the dewarped skull of sue, which simply isn't that deep:
encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQvCyHGTS4eME0JAZFYkfqKhix1l98mD8AAPIoCsTAFaFWjiz5dvg
encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSY2DwJ6FZoR6nMFqfSnP2WDs8GkemYh-4ZO4TStAqCclOTMm5P
you probably have other specimens, like stan in mind when envisioning a T. rex skull:

the maximum depth of the original is merely 45cm, and you have to keep in mind the deeper it gets the narrower it must logically get. when retaining it as 80-90cm wide, there is no way it could have been much deeper than the

I don't know. The rex skull sounds a bit weird. Many of the recontructions I've seen depict a skull somewhat deeper, more than this. Others comparisons of rex skull with by example Giganotosaurus (commonly found) does not show a such massive difference in skull depth.

Sincerely, your thread is very pleasant to read but I doubt of its absolute veracity in some details like this.

Regarding the skull of Giganotosaurus, I was thinking about this reproduction


Yours wears a somewhat odd protuberance on the mandible, exagerrated lobe in my opinion, and the skull, dspite its sheer length, is far too compressed.

It looks like a cross between an abelisaurid and carcharodontosaurid or allosaurid. Never seen such a skull suggestion for Giganotosaurus.

That's why, as worthwile it is, I would not take your scale as totally reliable. Hopefully, you can improve it with time.

[Grey]

Mar 2, 2013 16:27:41 GMT 5 theropod said:

here you go.

I only changed the maxilla and adjusted the nasals, everything else is identical in the two reconstructions. The lenght changed considerably, much more than I would have expected.
Decide for yourself which oen you like better, imo these two are good bounds but i cannot decide which oen I like better.

Both are interesting. A little preference for the one at the right.

However, what is that new size figure of 1,76 m ? I don't know any theropod with a skull that length, excluding, perhaps, Spinosaurus.
I agree we can speculate but please, don't bring carnivora forum stuff here.

[creature386]

Well, the highest estimate for Giga's skull which I can find comes at least close to it. I have measured an image of MUCPv-95's skull (it can be found in "Holtz Jr., T.R., Molnar, R.E., and Currie, P.J. (2004). Basal Tetanurae.") and I got something between 1,6 and 1,7 m.

[theropod]

Well, The most commonly mounted skull, even tough inaccurate, is significantly longer. What you see there is nothing but the scaled elements, scaled to an accurate quadrate size (coria & currie, 2001 I think).
Of course the shape will tend to vary, and as you see relatively slight changes can have significant effect. that doesn't mean one is more accurate than the other. The depth for example seems even more extreme because the skull is so compressed in my first reconstruction.

What you could do is push the jugal-lacrimal articulation further downwards, that would reduce the depth a bit, but not in any way significantly. I think what you want to see is a generally smaller skull, more elongate at the same lenght, which would be inconsistent with the fossils. based on what you can see in Coria & Salgado, using the quadrate measurement from Coria & Currie, it ends up that size and won't get significantly shallower.
If the skull gets more elongate, that just means it also gets longer.
This is no carnivoran speculation, it's the msot accurate possible way to restore it. Hartman's is not very different either.

Please have a look at Acrocanthosaurus skull for the other details, usually you will see the reason why they are reconstructed like that and not differently there:

www.plosone.org/article/fetchObject.action?uri=info:doi/10.1371/journal.pone.0017932.g002&representation=PNG_I

from Eddy DR, Clarke JA (2011) New Information on the Cranial Anatomy of Acrocanthosaurus atokensis and Its Implications for the Phylogeny of Allosauroidea (Dinosauria: Theropoda). PLoS ONE 6(3): e17932. doi:10.1371/journal.pone.0017932

[theropod]

As I would interpret things, the main feature that makes Giganotosaurus's skull so awkward looking is the very deep maxillary main body. There is little speculation about its size, it is the most accurate possible metod we have. for the 1,76m, of course it is ENTIRELY speculative. You said you found the skull too compressed, I made an alternate more elongated version and that's just what it ended up as. What isn't speculative at all is the size of the remains it bases on, so certain dimensions are given. the lower figure, 1,6m, is also speculative, but these two probably show a good range of possible sizes and shapes.

[theropod]

concerning sue, have a look at this:


I made a quick comparison of the original, the mounted skull and the digital dewarp used by McHenry in his thesis on Kronosaurus.

Sorry that it didn't turn out that nicely, but you can see the point, sues skull in the most widely distributed version looks just like mine, and the only difference in the other reconstructions (McHenry's looks very similar to Hartmans as far as I can tell Hartmans updated skull also rather looks like mine, strangely its size varies from the same as mine to a bit longer depending on the chart) only differ in having that concavity above the nasals removed, and possbly being slightly deeper.

Overal, T. rex skulls and sue's skull in particular are not particularly deep in absolute terms. They are very wide, and composed of very robust bones. Carnosaur skulls are deeper, they are laterally compressed and their more open built, with large fenestrae increases the optical effect even more.

I think It is possible the measurements in McHenry are a bit overestimated, since the skull seems deeper, longer AND wider than what you would predict from Brochu.

My Giganotosaurus skull reflects the size of the fossils, not what others may envision it as. The lower-end recosntruction is indeed very compresses, that is true. However you can fit all the remains into it. At the same size, you can not get the skull to be much shallower, no matter what you do.

[creature386]

So Carnosaur skulls are deeper, but Tyrannosaur skulls are wider.
This may support the idea of Spinosaurinae having porportionally stronger bite forces than other Spinosaurids, as Tyrannosaurs also have stronger bite forces than Carnosaurs.
Tough the robusticity seems to be about the same.

[theropod]

Let's not overgeneralize here, Skull width and depth alone don't tell us much about bite force. T. rex bite force was nearly twice stronger than that of Carcharododontosaurus, not surprising when looking at the width, bone structure and space for musculature.
However, the Carnosaur skulls that have been studied where shown to have been highly resistant nevertheless (unsurprisingly I'm mainly talking about Allosaurus here), they may have had relatively weak bite forces, but strong skulls in ventrodorsal direction. The lateral compression is advantageous for vertical strenght, but what it reduces, and what is also contraindicating a killing style similar to T. rex, is lateral strenght. obviously, an animal relying on powerful crushing bites needs to properly bite and hold onto its prey, at least for a short period of time, and produce a powerful opposition force, excerting some degree of lateral stress on the skull, and there has to be enough space for the muscles to attach at.

that's one of the reasons why I don't get how people tend to presume my Spinosaurus skull is so extremely narrow, it is still broader than Suchomimus' or irritators, even tough conservative in terms of width, and there aren't even other reconstructions.

For a strong bite force, the cranial resistance needed is a mixture of vertical and lateral strenght; vertical to resist the bite itself, this is the essential part to deal mechanical damage to a prey item, and lateral to absorb struggling forces and the pulling loads of its own muscles. Then, other aspects like the way forces are absorbed also come into this. In T. rex case, creature provided evidence for a kind of shock absorber in T. rex, based on many skull bones not really being fused. I'd presume this is too a part of the apparatus to handle a prey item once it has bitten down on it.

Carcharodontosaurs on the other hand probably avoided this whole thing by applying quick bites in a strict dorsoventral plane, with a very short phase of contact. Logically lateral strenght wasn't so important for them, and they focused on vertical strenght-hence the deep, narrow skulls in these taxa.
Also, because they rather relied on tooth sharpness, they didn't need the strong bite force and excessive musculature.

To summarize: in crushers/puncturers/shakers like T. rex, selective pressure favoured the developement of a moderately deep, very wide skull.
in slicers/pullers/slashers like carcharodontosaurus, selective pressure favoured deep but narrow skulls

Just a summary of my interpretation of their respective skull morphologies, however you can find this hinted in most of the major works done on theropod crania.

Spinosaurinae are a different story; they are not primarily optimized to deal damage using their jaws, but to be effective at catching fish and smaller prey. A streamlined, elongated shape and a very fast bite and conical gripping teeth were logically the most advantageous here, which doesn't mean they didn't quite likely have a moderately strong bite force, but their focus was not primarily on being effective as killing tools, contrary to Carnosaurs and Tyrannosaurs in which this is reflected by their respective adaptions.
A very long jaw naturally means the mechanical advantage near the front (the part that will be the most likely to come in contact with the prey or opponent) isn't as good as in a shorter jaw, nor is it as stable.
One important thing to note here is that them having broader skulls than Baryonychines seems to be a myth, just have a look at this picture I found on Cau's blog:

[blaze]

theropod
Where can I get Dr. Colin McHenry thesis? btw how's your reconstruction of the Torvosaurus skull going?

@creature
There's a little error in your table, the distorted skull of the Acrocanthosaurus Fran is the one that's 123cm long, undistorted it's ~129cm, that's mentioned in the paper where it's described.

[theropod]

blaze: nova.newcastle.edu.au/vital/access/manager/Repository/uon:12164
originally grey posted this on Carnivora

My Torvosaurus? There are hardly any improvements, and I'm extremely busy at the moment, preparing school stuff. To be honest, it didn't end up good enough to upload it and I'll have to revise a lot in order to create a good reconstruction.

[creature386]

blaze, Thanks!
BTW, what do you think of the 1,19 m figure for Suchomimus' skull? Because carnivora member Spinodontosaurus has shown that this could be underestimated.

theropod, good luck with your school stuff!
(I aswell have to prepare myself)