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Post by lionclaws on Sept 22, 2023 20:18:09 GMT 5
Gotten myself down the AvA rabbithole (again), but I want to engage a bit more professionally this time, at least until I regain "command of the sources" like I used to have.
Been reviewing a study I found fascinating back in my debating days:
If I'm understanding correctly, Snively and Russell conclude that Tyrannosaurs were very strong lateral and dorsiflexive motions, but their necks were relatively inflexible. On the other end of the spectrum, Ceratosaurus and Allosaurus had fairly flexible necks, and seem to have been capable of moving their heads at higher speeds.
Abelisaurs are mentioned a lot, but (annoyingly) detailed examination of their craniocervical dynamics aren't given in detail.
Animals like Acrocanthosaurus and Giganotosaurus aren't treated at all, sadly.
I have read on Acrocanthosaurus' animal profile that its neck was less flexible (and perhaps stronger?) than typical for a theropod of its clade, and based on what I can find, it's occiput superficially resembles that of Albertosaurus.
So, I'd like to open up the floor. Anyone who knows theropods, what were the Abelisaurs and Carcharodontosaurs doing?
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Post by theropod on Sept 22, 2023 21:15:07 GMT 5
You are referring to this passage from the Acrocanthosaurus profile, I suspect? TBH I am not sure what this is based on, and some of it seems incorrect ( Acrocanthosaurus doesn’t really have a "deeper skull compared to previous allosaurs", and the claim of it being larger looks like it is specifically based on vanilla- Allosaurus (and not any of the multiple specimens of very large Morrison allosauroids that were clearly at least in a similar size range to large Acrocanthosaurus specimens. As far as the thicker, stronger neck is concerned, this is likely simply an interpretation based on the elongate neural spines. Which does make sense, in a way. These processes would certainly have made its neck less flexible, at least in dorsiflexion, than that of Allosaurus (noted for its anteroposteriorly long but dorsoventrally low neural spines). But whether this would also affect lateral mobility is unclear; as you say, it has never been studied in detail. Also depending on whether the spines served to anchor substantial musculature, or just mostly ligaments, whether the neck was particularly strong overall is unclear too. I remember trying to determine something about craniocervical dynamics in Acrocanthosaurus, Carcharodontosaurus ( iguidensis), and Giganotosaurus a few year ago, and it looking like the former two had ventrally depressed paroccipital processes (as an adaptation for forceful ventroflexion of the head), but perhaps not as extreme as the condition seen in Allosaurus, especially for Carcharodontosaurus (though the process seems incomplete, so no guarantees, see Eddy and Clarke 2011 and Brusatte and Sereno 2007). In Giganotosaurus on the other hand, it looks like the processes terminate dorsal to the occipital condyle, which would mean muscles attaching there could not impart a ventroflexive moment (see Coria and Currie 2003) but the braincase is also incomplete in this region, so I am not completely sure. My interpretation of that was that early-branching allosaurs (early-branching with respect to giganotosaurine-line carcharodontosaurids) like Allosaurus tended to have more emphasis on ventroflexion of the neck, whereas on the lineage to giganotosaurines this was gradually reduced in favour of proportionately larger, more elongated skulls, perhaps more relying more on the sheer length of the tooth rows. But what exact functional consequences that would have would be a fairly complex thing to figure out. Right now we don’t even have a decent three-dimensional description of the skull of Giganotosaurus; literally the only published information is a few sentences and a few grainy shots in lateral view, not even showing all the bones that are preserved. So having a rigorous 3D reconstruction of the entire skull would be crucial to getting a better understanding of its head and neck function. Regarding Abelisaurs, their neck morphology converges more with Tyrannosaurs in having thick vertebrae with long processes (strongly enlarged epipophyses in the case of Abelisaurs), which likely would have made the neck strong, but rather inflexible. This however too has not been quantitatively studied, although the anatomy has been well-described, for example by Mendez (2012). I think it would be really valuable to have a more in dept, quantitative look at head and neck function in abelisaurs. There are 3D models for the skull of Majungasaurus available if anyone wants to try their hand at it: www.morphosource.org/catalog/media?utf8=%E2%9C%93&locale=en&search_field=all_fields&q=majungasaurusThey are clearly a weird mixture of contradictory features seen in other theropods, really robust, strong necks and short, robust skulls, but coupled with small, bladelike teeth. I’m still really confused by how they functioned. --- Brusatte, S.L. and Sereno, P.C. 2007. A new species of Carcharodontosaurus (Dinosauria: Theropoda) from the Cenomanian of Niger and a revision of the genus. Journal of Vertebrate Paleontology 27 (4): 902–916. Coria, R.A. and Currie, P.J. 2003. The braincase of Giganotosaurus carolinii (Dinosauria: Theropoda) from the upper cretaceous of Argentina. Journal of Vertebrate Paleontology 22 (4): 802–811. Eddy, D.R. and Clarke, J.A. 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. Méndez, A.H. 2012. The cervical vertebrae of the Late Cretaceous abelisaurid dinosaur Carnotaurus sastrei. Acta Palaeontologica Polonica 59 (3): 569–580.
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Post by lionclaws on Sept 22, 2023 23:13:20 GMT 5
You are referring to this passage from the Acrocanthosaurus profile, I suspect? TBH I am not sure what this is based on, and some of it seems incorrect ( Acrocanthosaurus doesn’t really have a "deeper skull compared to previous allosaurs", and the claim of it being larger looks like it is specifically based on vanilla- Allosaurus (and not any of the multiple specimens of very large Morrison allosauroids that were clearly at least in a similar size range to large Acrocanthosaurus specimens. I was actually referring to this post: I don't know if this has become outdated since then, but this book proposes that the spine of Acrocanthosaurus was covered in extensive ligamenture and heavily muscled. The spine is proposed to have sacrificed some flexibility for greater strength, presumably to prey upon giant sauropods ( Harris, 1998). Of course, this isn't to say the vertebral column was completely stiff. After all, the cervical and cranial dorsal vertebrae were still strongly opisthocoelous. I don't know what "opisthocoelous" means, but it seems to indicate flexibility. What's your take on the source in question? Reconstructions of Acrocanthosaurus' skull seem a little more complete, FWIW, which is one of the reasons I'm semi-fixated on that specific Carcharodontosaur. If you had to guess, where on the "fast and flexy" to "stiff and strong" neck spectrum would you expect Acrocanthosaurus to land? Based on limited evidence and my own equally limited understanding, I'm inclined to think that it was stronger than Allosaurus and Ceratosaurus in lateral motion, and (while not as strong) faster and more flexible than comparable Tyrannosaurs. That being said, I am interested in a professional's take. I'm glad to know that those with some expertise on the subject feel the same way I do about Abelisaurs, lol. I was always an avid user of the Therrien et al study on theropod mandibles. The lower jaws of the abelisaurids studied were not particularly well adapted to lateral/torsional stresses compared to a tyrannosaurid (say), but run-of-the-mill for theropods generally, and that could have been offset by a sufficiently flexible intramandibular joint (which Carnotaurus, at any rate, seems to have had). If the lower jaw isn't held rigid, it won't experience as much stress. "The tree is blown over, the reed returns to true," or something like that. My (tentative) assumption would be that Abelisaurs would thrash prey violently, ripping out bleeding chunks. Tyrannosaurs seem to have had a similar "shaking" style, but they had railroad spikes instead of scapels for teeth, so they would be ragdolling prey rather than taking out chunks. The difference in mandibular profile may indicate that the Tyrannosaurs' higher bite forces meant that they couldn't rely on mandibular flexibility to evade stresses, and thus had to tackle them head-on with thicker bones. Carnosaurs (and other theropods with relatively laterally compressed skulls) strike me more as "slash'n'saw" biters, keeping relatively brief contact with prey, but bringing the entire tooth row to bear in long anterioposterior motions. Alternatively, against larger prey, they may have relied primarily on the anterior teeth to deliver long slashing wounds across the entire arc of the bite, as Therrien et al found evidence of the anterior mandible being relatively well reinforced for Ceratosaurus, Allosaurus, Acrocanthosaurus, and Giganotosaurus.
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Post by Infinity Blade on Sept 23, 2023 2:22:19 GMT 5
I saw what was going on in this thread and felt the need to respond once I got back home from work. TBH I am not sure what this is based on, and some of it seems incorrect ( Acrocanthosaurus doesn’t really have a "deeper skull compared to previous allosaurs", and the claim of it being larger looks like it is specifically based on vanilla- Allosaurus (and not any of the multiple specimens of very large Morrison allosauroids that were clearly at least in a similar size range to large Acrocanthosaurus specimens. The reference I cited for this claim when creating the profile was the 2016 “Sauropods: Life in the Age of Giants” book. And at one point it says (p. 306): I wonder if it’s possible that they were just comparing Acrocanthosaurus and earlier allosaurs in absolute terms. But on my end, the book was written in part by Matt Wedel, so I just kind of took his word for it, even if I don’t completely agree with everything said here (particularly the characterization of Acrocanthosaurus’ arms as “relatively weak”). My (tentative) assumption would be that Abelisaurs would thrash prey violently, ripping out bleeding chunks. Tyrannosaurs seem to have had a similar "shaking" style, but they had railroad spikes instead of scapels for teeth, so they would be ragdolling prey rather than taking out chunks. The difference in mandibular profile may indicate that the Tyrannosaurs' higher bite forces meant that they couldn't rely on mandibular flexibility to evade stresses, and thus had to tackle them head-on with thicker bones. I think you pretty much got it. In fact, Sampson et al. (2007) (hyperlinked) proposed that while Majungasaurus would have used relatively fewer, prolonged penetrating bites to hold onto prey, they also believe that powerful neck retraction was used to produce grievous wounds onto prey (even saying this is in accord with Therrien et al.’s findings). My interpretation of abelisaurid teeth is that they were a compromise between being strong enough for holding onto violently struggling prey for prolonged periods (as well as eating bone, which at least Majungasaurus seems to have done) and being well shaped for slicing flesh. They were relatively short-crowned, which would have made them less liable to break when holding onto prey or eating bone, but were still ziphodont teeth that could slice flesh if they really wanted to. Tyrannosaurids were similar, I think. Except while abelisaurids had small ziphodont teeth they replaced much more frequently than other theropods did ( D'Emic et al., 2019), tyrannosaurids had stout serrated railroad spikes that were much longer lasting to hold onto prey, tear open massive wounds (like a spotted hyena, crocodile, or orca, but with teeth arguably better suited for this job), and of course, crush bone. Btw, I assume you're the LionClaws of Carnivora forum? I don't know if you remember me, but it's really good to see you around here!
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Post by theropod on Sept 23, 2023 4:06:37 GMT 5
Thank you both for clearing that up and the reference, I had overlooked that source added below on the profile.
Opisthocoelous means concave on the posterior end of the centrum, convex on the anterior end, i.e. ball-and-socket joints (which as you correctly surmise is an indicator of relatively high flexibility, and a fairly typical condition for non-avian theropod necks, though developed to differing degrees).
Seems reasonable. While the interpretation is speculative, I’d agree that the tall neural spines would imply greater rigidity and strength, although it’s important to note that the exact amount of musculature that attached to them is unknown, and probably always will be. How much musculature there was, and how far it bulged out laterally, would also have an influence on the amount of lateral flexibility the neck would have retained.
Quite understandable, it has not received nearly the amount of attention that its skeletal completeness would warrant.
Allosaurus I would likely agree on, as Allosaurus’ neck is uniquely adapted for ventroflexion at the expense of modifying lateroflexors (the iliocostalis capitis and longissimus capitis superficialis) into ventroflexors (these muscles would still also have performed lateroflexion too, but their moment arms for lateroflexion were likely comparatively smaller than if the paroccipital processes were purely laterally oriented, as in other theropods. I am unsure as to what degree muscles originating from the elongate neural spines might contribute to lateroflexion of the neck, so not sure about Ceratosaurus (which has the more "standard" theropod condition with laterally facing paroccipital processes). Ceratosaurus honestly deserves its own discussion in terms of craniocervical function.
That being said, I strongly suspect the neck was more mobile laterally, and (even if mainly due to the much lighter skull) more geared towards moving quickly than in Tyrannosaurus, which, as the source quoted above points out, has central articulations permitting much less mobility between adjacent vertebrae.
Yes, there’s this general trend towards a strenghthening of the mandibular symphysis, but I wonder if it really has something to do with this, or with using the anterior end of the jaws for prey restraint. For one, the premaxillary teeth of most theropods are thicker and less blade-shaped than the more posterior ones, indicating they had a different function. In tyrannosaurids they have the classic "D-shaped" cross-section, and are also much smaller than the lateral, which is commonly interpreted as an adaptation for defleshing carcasses, but even in Allosaurus the premaxillary teeth look very different from the maxillary ones. Also, while the symphysial region itself is thickened, I have my doubts if this is really an adaptation for using this part of the jaws for forceful biting. Mechanically, this interpretation (whether for killing bites or prey restraint) doesn’t really make sense; as long as the mandible was used to deliver bite force, that bite force would also always be stronger further distally/posteriorly, and having a strong anterior region would be of no use if the more posterior parts weren’t able to stand up to this load (in fact the bending moments would be stronger on the middle of the mandible than they would be on the tip, even if the bite was delivered at that tip; think of it like bending a branch with your two hands. That branch is going to bend most, and eventually snap, in the middle, not near the ends where you are holding it). So if withstanding forces from biting near the symphysis was the purpose of the deepened mandibular symphyses we often see in theropods, the mandibles would be in much greater need of strengthening more posteriorly than they would at the symphysis.
My hypothesis would be that the anteriormost teeth in the dentary and those in the premaxilla were likely used for defleshing carcasses, and perhaps, to some limited extend, for grasping small prey, but that the long, bladelike teeth in the mid-maxillary region where the primary killing tools across most groups of large theropods. Allosaurs in particular likely had the gape angles necessary to bring these teeth to bear effectively on large prey (Bakker 1998, Lautenschlager et al. 2015), and the mid-maxillary region is also where their skulls appear to be reinforced to withstand large forces from a combination of biting and ventroflexion of the neck. On the other hand, the deeper symphysial region may be related not to making this region of the mandible stronger than the rest in relation to loads specifically applying there, but rather to the need to strengthen the symphysial articulation between the mandibular rami by increasing the contact area of the symphysial joint (hence why this area is expanded dorsoventrally, sometimes extremely, as in Giganotosaurus, but not so much mediolaterally).
Yes, as I recall they found convergence in the strength profiles of the mandibles of Abelisaurids and Antrodemus=Allosaurus, even though I think for simplicity they only compared the strength profiles of individual mandibular rami. I do wonder if we’d see greater separation between Abelisaurids and other theropods if the 3D arrangement of the rami were taken into account, as two rami of the exact same dimensions and cross-sectional strength properties, but taken together, will have very different lateral bending strength when taken together depending on how far apart they are spaced, and Abelisaurs appear to have had fairly wide, u-shaped mandibles compared to other theropods. Not sure if I’m bringing the point I mean to make across very well, what I mean is that while this will have no effect on dorsoventral bending strength, for the lateral stiffness of the mandible it matters a lot if the rami are close together or far apart in the transverse plane, even if the rami themselves have the exact same strength properties.
I believe something similar (high bending strength indicators) was noted for Sinraptor teeth by Snively et al. 2006, and at least implied based on the relatively short teeth of Allosaurus by other authors.
Of course to reduce bending moments, one can either increase the section modulus of the teeth (i.e. make them wider and thicker) or make them shorter, and it looks like Abelisaurs and at least some carnosaurs did the latter, whereas Tyrannosaurus did the former.
In fact allosauroids and tyrannosaurs have very similar anteroposterior bending strength indicators of their teeth (computed as section modulus divided by crown height) at similar skull length according to Snively et al. 2006, but Tyrannosaurus has mediolaterally much stronger teeth than allosauroids of similar skull length (and Carnotaurus in fact has much stronger teeth than anything else at similar skull length, although it has to be said that it also simply has a much smaller skull at similar body length). The trends for bending strength indicators of the whole skull (second moments of areas modelled as a hollow shell with trapezoidal cross-section) seem to be similar between allosauroids and tyrannosaurs, with most taxa being very similar for a given skull length, but T. rex having much greater area moments (about two times the dorsoventral and three times the mediolateral strength) than similar-sized allosauroid skulls (coincidentally, this all fits in quite well with bite force estimates giving large T. rex specimens about two times the bite force of Giganotosaurus).
Sadly Snively et al don’t seem to have modelled the area moments for the skulls of the ceratosaurs, that would be an interesting thing to analyze. I wonder if it might be feasible to produce comparative figures for ceratosaurs using the same methodology as Snively et al., as it’s basically just based on the external dimensions of the skull. The only thing I’m unclear on is how exactly they determined all proportions of the trapezoids (specifically the relative length of the dorsal and ventral edges) based on only knowing dorsoventral and transverse dimensions of the entire structures. How to go about calculating the approximated area moments from there seems reasonably straighforward.
--- Bakker, R.T. 1998. Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues. Gaia 15: 145–158. Lautenschlager, S. 2015. Estimating cranial musculoskeletal constraints in theropod dinosaurs. Royal Society open science 2 (11): 150495. Snively, E. and Russell, A.P. 2007. Functional variation of neck muscles and their relation to feeding style in Tyrannosauridae and other large theropod dinosaurs. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology: Advances in Integrative Anatomy and Evolutionary Biology 290 (8): 934–957. Snively, E., Henderson, D.M. and Phillips, D.S. 2006. Fused and vaulted nasals of tyrannosaurid dinosaurs: implications for cranial strength and feeding mechanics. Acta Palaeontologica Polonica 51 (3). Snively, E., Cotton, J.R., Ridgely, R. and Witmer, L.M. 2013. Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda). Palaeontologia Electronica 16 (2): 1–29.
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Post by lionclaws on Sept 23, 2023 23:48:13 GMT 5
I saw what was going on in this thread and felt the need to respond once I got back home from work. ... My (tentative) assumption would be that Abelisaurs would thrash prey violently, ripping out bleeding chunks. Tyrannosaurs seem to have had a similar "shaking" style, but they had railroad spikes instead of scapels for teeth, so they would be ragdolling prey rather than taking out chunks. The difference in mandibular profile may indicate that the Tyrannosaurs' higher bite forces meant that they couldn't rely on mandibular flexibility to evade stresses, and thus had to tackle them head-on with thicker bones. I think you pretty much got it. In fact, Sampson et al. (2007) (hyperlinked) proposed that while Majungasaurus would have used relatively fewer, prolonged penetrating bites to hold onto prey, they also believe that powerful neck retraction was used to produce grievous wounds onto prey (even saying this is in accord with Therrien et al.’s findings). My interpretation of abelisaurid teeth is that they were a compromise between being strong enough for holding onto violently struggling prey for prolonged periods (as well as eating bone, which at least Majungasaurus seems to have done) and being well shaped for slicing flesh. They were relatively short-crowned, which would have made them less liable to break when holding onto prey or eating bone, but were still ziphodont teeth that could slice flesh if they really wanted to. Tyrannosaurids were similar, I think. Except while abelisaurids had small ziphodont teeth they replaced much more frequently than other theropods did ( D'Emic et al., 2019), tyrannosaurids had stout serrated railroad spikes that were much longer lasting to hold onto prey, tear open massive wounds (like a spotted hyena, crocodile, or orca, but with teeth arguably better suited for this job), and of course, crush bone. I'm not sure if I agree with the feline comparison. Felines typically restrain prey with their forelimbs before delivering a precise bite to the throat or spine. For the largest prey items, they use their flexible lips to form a tight seal over the prey's nose and mouth. Very few theropods could restrain prey with thsir forelimbs and bite it at the same time (IIRC, Spinosaurs and Dromaeosaurs were the major exceptions), and while dinosaurs probably did have lips, they probably weren't mobile enough to be used to suffocate prey. The general conclusion of "fewer and deeper bites" I can definitely see, though, and if we recognize that they're trying to rip the throat out rather than simply crush it, I can definitely see targeted bites being a thing. One and the same. Assuming you're Ceratodromeus, it's good to see you again!
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Post by Infinity Blade on Sept 24, 2023 0:07:40 GMT 5
I'm not sure if I agree with the feline comparison. Felines typically restrain prey with their forelimbs before delivering a precise bite to the throat or spine. For the largest prey items, they use their flexible lips to form a tight seal over the prey's nose and mouth. Very few theropods could restrain prey with thsir forelimbs and bite it at the same time (IIRC, Spinosaurs and Dromaeosaurs were the major exceptions), and while dinosaurs probably did have lips, they probably weren't mobile enough to be used to suffocate prey. The general conclusion of "fewer and deeper bites" I can definitely see, though, and if we recognize that they're trying to rip the throat out rather than simply crush it, I can definitely see targeted bites being a thing. Yeah pretty much. The comparison to big cats Sampson et al. make isn’t an exact one, only connected with the “fewer deeper bites” part. Also, I didn’t know cats used their lips to help suffocate prey, damn! It makes sense, though. I’m actually Ausar. Ceratodromeus isn’t around anymore, unfortunately.
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