Functional Morphology of Animal Feeding Apparata

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New paper just dropped that found that aetosaurs had powerful bites. I find the conclusion that they were more faunivorous to be...questionable.

laplata.conicet.gov.ar/reconstruyen-en-3d-el-craneo-de-un-primitivo-ancestro-de-los-cocodrilos-y-confirman-que-se-alimentaba-de-otros-animales/

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I just learned that flat-headed temnospondyls like Gerrothorax opened their mouths by lifting their heads up (like a toilet seat) instead of lowering their jaws. I literally thought this was impossible among vertebrates. And apparently they're not even the only amphibians that do this.



www.tandfonline.com/doi/abs/10.1671/0272-4634-28.4.935

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Finite element analysis of cingulate jaws.

www.ncbi.nlm.nih.gov/pmc/articles/PMC4412537/

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Recent information on Effigia.

“Effigia okeeffeae exhibits an ‘ostrich-like’ bauplan comprising a gracile skeleton with edentulous jaws and large orbits, similar to ornithomimid dinosaurs and extant palaeognaths,” said lead author Dr. Jordan Bestwick from the School of Geography, Earth and Environmental Sciences at the University of Birmingham and colleagues.

“This bauplan is regarded as an adaptation for herbivory, but this hypothesis assumes morphological convergence confers functional convergence, and has received little explicit testing.”

In the study, the authors used new CT scans of Effigia okeeffeae’s skull which revealed a much more accurate reconstruction of the animal.

This included new information about the shape of the skull, such as a more rounded, bulbous brain cavity and curved upper and lower jaws.

Unlike an ostrich bill, which is more rounded, Effigia okeeffeae’s bill is more concave with jaws that open and close a bit like a pair of shears.

The researchers used this information to model the effects of different forces acting on the skull, including what happens when the animal pecks at the ground.

By modeling the forces the skull would need to withstand in order to feed by pecking, the scientists calculated that Effigia okeeffeae’s skull would probably have shattered.

Instead, they suggest, the animal would be more likely to use its jaws to snip off and nibble pieces of soft plant material such as young shoots, or ferns.

“The herbivores we already recognize in the Triassic period fed either by digging for roots, such as the pig-like aetosaurs, or reaching for leaves high up in the treetops, like the long-necked sauropods,” Dr. Bestwick said.

“These two-legged browsers with a weak bite are unique to this period and show a previously unrecognized diversity among the herbivores of this period.”

www.sci-news.com/paleontology/effigia-okeeffeae-10313.html


Below is the abstract to the study this article discusses.

Pseudosuchians, archosaurian reptiles more closely related to crocodylians than to birds, exhibited high morphological diversity during the Triassic with numerous examples of morphological convergence described between Triassic pseudosuchians and post-Triassic dinosaurs. One example is the shuvosaurid Effigia okeeffeae which exhibits an “ostrich-like” bauplan comprising a gracile skeleton with edentulous jaws and large orbits, similar to ornithomimid dinosaurs and extant palaeognaths. This bauplan is regarded as an adaptation for herbivory, but this hypothesis assumes morphological convergence confers functional convergence, and has received little explicit testing. Here, we restore the skull morphology of Effigia, perform myological reconstructions, and apply finite element analysis to quantitatively investigate skull function. We also perform finite element analysis on the crania of the ornithomimid dinosaur Ornithomimus edmontonicus, the extant palaeognath Struthio camelus and the extant pseudosuchian Alligator mississippiensis to assess the degree of functional convergence with a taxon that exhibit “ostrich-like” bauplans and its closest extant relatives. We find that Effigia possesses a mosaic of mechanically strong and weak features, including a weak mandible that likely restricted feeding to the anterior portion of the jaws. We find limited functional convergence with Ornithomimus and Struthio and limited evidence of phylogenetic constraints with extant pseudosuchians. We infer that Effigia was a specialist herbivore that likely fed on softer plant material, a niche unique among the study taxa and potentially among contemporaneous Triassic herbivores. This study increases the known functional diversity of pseudosuchians and highlights that superficial morphological similarity between unrelated taxa does not always imply functional and ecological convergence.

anatomypubs.onlinelibrary.wiley.com/doi/abs/10.1002/ar.24827

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I highly recommend reading about this physical experiment on sabertooth jaws and teeth. According to it, scimitar-tooths bit down in line with the tooth axis when biting with the mandible; the mandible could then be released and the teeth could be drawn back and enlarge the wound. Dirk-tooths, however, carve through prey in a continuous arc and the force is perpendicular to the tooth axis; this produces a wound several times wider than the fore-and-aft width of the tooth and the trajectory allows the teeth to cut themselves out without needing to open the mouth.

Scimitar-tooths could have a default bite using only their large incisor arcade if their specialized killing bite doesn't work on a particular prey item (like juvenile proboscideans), while dirk-tooths lacked an alternative or default bite to seriously wound prey unsuited to their killing bite.

www.google.com/books/edition/The_Other_Saber_tooths/2GjhrKO9y74C?hl=en&gbpv=1&bsq=experimental%20paleontology%20of%20the%20scimitar-tooth%20and%20dirk-tooth%20killing%20bites

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Macroevolutionary trends in theropod dinosaur feeding mechanics

• A general trend of jaw strengthening is observed along all theropod lineages
• Carnivores and herbivores achieved this via different morphofunctional modifications
• Same jaw strengthening trend is also detected in tyrannosaurids ontogenetically
• This common trend is linked to functional peramorphosis of bone functional adaptation

Theropod dinosaurs underwent some of the most remarkable dietary changes in vertebrate evolutionary history, shifting from ancestral carnivory to hypercarnivory and omnivory/herbivory, with some taxa eventually reverting to carnivory. The mandible is an important tool for food acquisition in vertebrates and reflects adaptations to feeding modes and diets. The morphofunctional modifications accompanying the dietary changes in theropod dinosaurs are not well understood because most of the previous studies focused solely on the cranium and/or were phylogenetically limited in scope, while studies that include multiple clades are usually based on linear measurements and/or discrete osteological characters. Given the potential relationship between macroevolutionary change and ontogenetic pattern, we explore whether functional morphological patterns observed in theropod mandibular evolution show similarities to the ontogenetic trajectory. Here, we use finite element analysis to study the mandibles of non-avialan coelurosaurian theropods and demonstrate how feeding mechanics vary between dietary groups and major clades. We reveal an overall reduction in feeding-induced stresses along all theropod lineages through time. This is facilitated by a post-dentary expansion and the development of a downturned dentary in herbivores and an upturned dentary in carnivores likely via the “curved bone effect.” We also observed the same reduction in feeding-induced stress in an ontogenetic series of jaws of the tyrannosaurids Tarbosaurus and Tyrannosaurus, which is best attributed to bone functional adaptation. This suggests that this common tendency for structural strengthening of the theropod mandible through time, irrespective of diet, is linked to “functional peramorphosis” of bone functional adaptations acquired during ontogeny.

www.cell.com/current-biology/fulltext/S0960-9822(21)01646-8?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982221016468%3Fshowall%3Dtrue

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We here briefly discuss the biting and feeding style of Qianzhousaurus, as inferred from gross osteology of the skull. Three general observations suggest that Qianzhousaurus, unlike its deep-snouted cousins, would not have been a particularly hard biter. First, its teeth are intermediate between the mediolaterally thin ziphiform teeth of Alioramus altai and the robust, peg-like incrassate condition seen in adult derived tyrannosaurids. Second, although more robust than Alioramus, the skull bones of Qianzhousaurus are generally more gracile, with thinner rami and less reinforced sutures, than are those of deep-snouted tyrannosaurids (Rayfield, 2004, 2005a, b). Third, Qianzhousaurus possesses relatively smaller muscle attachment sites and evident muscle scarring relative to deep-skulled tyrannosaurid specimens (Hurum and Currie, 2000)—for instance, the flange for the adductor muscles above the surangular shelf and the muscle attachment site on the dorsal prong of the surangular anterior ramus are relatively smaller than those of deeper-snouted tyrannosarids. We thus predict that Qianzhousaurus would have filled a different ecological niche from large-bodied tyrannosaurids such as Tarbosaurus.

It is notable that alioramins existed in sympatry with deep-snouted tyrannosaurids. We envision that alioramins—both the smaller and more gracile Alioramus individuals and the moderately larger and more mature Qianzhousaurus holotype individual—would have been nimbler, perhaps more active pursuit predators than the hard-biting, but slower and stockier, apex predators such as Tarbosaurus. Recent research into tyrannosaurid-dominated ecosystems finds that the diversity of large-bodied theropods in these faunas is remarkably low, which is likely due to ontogenetically controlled niche partitioning within single species, with juvenile tyrannosaurids filling niches traditionally occupied by separate taxa of small–medium sized theropods in non-tyrannosaurid-dominated environments (Woodward et al., 2020; Garcia-Giron et al., 2021; Holtz, 2021; Schroeder et al., 2021). This does raise a key question about the ecology of alioramins: were Alioramus and Qianzhousaurus also competing with the juveniles of their deep-skulled cousins? If so, how was this possible? Were there other anatomical, behavioral, or environmental factors that helped them partition niches? It also remains mysterious why there were separate taxa of long-snouted tyrannosaurids (alioramins) in Asia at the very end of the Cretaceous, but not in the even better-sampled North America.

We here propose some hypotheses, which can be tested with future study. We suggest that the long and delicate snout of alioramins effectively barred them from killing the same prey as both juveniles and subadults of Tarbosaurus bataar. We hypothesize there was little dietary competition between the lineages, although subadult and adult Ta. bataar could have preyed upon the smaller and relatively defenseless (aside from speed) alioramins. The specialized alioramin snout and dentition prevented competitive overlap, in terms of diet, between the sympatric lineages. Likewise, juvenile and subadult Ta. bataar of the same size as alioramins had higher bite forces that prevented or modulated competition since they could capably attack large prey that alioramins could not kill. In terms of Asian tyrannosaurine evolution, we propose that the slender alioramin skull was in a novel gracile lane (there is no analog of alioramins in the Laramidia or Appalachia subdivisions of North America in the Cretaceous), perhaps limited to killing small animals, whereas the boxy skull of Ta. bataar stayed in the ancestral lane of killing large animals. In contrast to the situation in Laramidia, where competition for similar prey could not have been avoided between Gorgosaurus libratus and Daspletosaurus torosus (given their similar morphotypes; cf. Russell, 1970), alioramins evolved specializations that, beyond preventing competition with Ta. bataar, secured their place in Upper Cretaceous Asian terrestrial ecosystems, presumably all the way up to the K/Pg extinction event.

We note that what is outlined above is at the hypothesis stage. Our prediction that Qianzhousaurus (and Alioramus) were weaker biters not capable of puncture-pull feeding needs to be tested explicitly using biomechanical analysis, such as Finite Element Analysis like that performed for other tyrannosaurids (Rayfield et al., 2001; Meers, 2003; Rayfield, 2004; Rayfield, 2005a, b; Rowe and Snively, 2021). Such analyses will be the best judge of the bite force estimates and structural integrity of the longirostrine alioramin skull, and how they compare with deep-snouted tyrannosaurids, and what that implies about dietary differences and niche partitioning. In addition to the discovery of even more mature (e.g., fully adult) alioramin specimens, such biomechanical analyses will be the next step in understanding the growth, feeding, and paleobiology of the unusual, long-snouted tyrannosaurids that lived at the same time as their deep-snouted kin, at the very end of the Age of Dinosaurs.

www.tandfonline.com/doi/full/10.1080/02724634.2021.1999251#.YgaCKTJG-Ko.twitter

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It looks like spinosaurids had unusually high tooth replacement rates.

Mateus & Estraviz-López (2022)

Regarding the inner anatomy of ML1190-1, the lack of a significant number of studies of this type in the dentary (usually they are centered around the premaxilla and maxilla of spinosaurids or other Mesozoic reptiles [89, 90], as complete dentaries are not common even in other theropods [91]) precludes us from reaching significant conclusions that might have systematic significance within the Spinosauridae group itself. Compared with the replacement pattern seen in Tyrannosaurus one of the biggest differences is the amount of secondary replacement teeth, both in the first five alveoli and further back in the mandible. In a specimen of Tyrannosaurus only one secondary replacement tooth is present in the fourth alveolus of the right dentary [92], and in Australovenator no secondary replacement teeth appear, with even some alveoli lacking replacement teeth altogether [93]. The presence of numerous replacement teeth compared with other theropods points towards a faster replacement rate of teeth, as seen in Spinosaurus [94], and indicates that this adaptation, which could have been related to piscivory, dates back to the early evolution to the clade. The extent of the secondary replacement teeth in the anterior alveoli of the dentary means that the condition proposed by Hendrickx et al. [29] as synapomorphic for Spinosauridae (“Dentary rosette of four teeth’’) can be rephrased as “Dentary rosette of at least four teeth’’ or “Dentary rosette with four alveoli”.

Heckeburg & Rauhut (2020)

High numbers of spinosaurid teeth found in Morocco suggest that this clade was very abundant during the "Mid-"Cretaceous in northern Africa. Several reasons have been proposed to account for this abundance of spinosaur teeth, from sampling biases to ecology. However, the number of teeth in the fossil record also depends strongly on the tooth replacement rate. So far, little is known about the tooth formation time and replacement rates in spinosaurids. Here, we analysed the histology of several spinosaur teeth to estimate tooth formation time and replacement rates, using the count of lines of von Ebner, the daily formed incremental lines in the dentine of the teeth. Line counts indicated a maximum tooth formation time of 271 days, and replacement rates were predicted to be between 59 and 68 days. These rates are faster than in other large theropods for which data are known, and, together with the rather high number of teeth in a spinosaurid dentition, might thus help to explain the abundance of spinosaur teeth in the "Mid-"Cretaceous of northern Africa.

However, a specialization on small and elusive prey that had to be caught and secured in the jaws might help to explain the fast replacement rates of spinosaurs compared to other theropods. Securing live and struggling prey in the jaws would exert rather large forces on individual teeth, increasing the danger of losing teeth during feeding. Apart from the relatively high tooth count (at least in baryonichines), more robust, conical shape of the teeth and the extremely deep implantation in the jaws (e.g., Charig and Milner, 1997; Rauhut, 2001a), fast replacement rates would be of advantage to keep the number of functional teeth high.

Despite their specializations for piscivory, spinosaurids had some impressive aspects about their dentition. I can see how these things were able to go after medium-sized dinosaurs too (like the Baryonyx found with juvenile Iguanodon remains in its gut).

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This new study confirms high bite forces in oviraptorosaurs.

Cranial muscle reconstructions quantify adaptation for high bite forces in Oviraptorosauria

Oviraptorosaurians are an unusual and probably herbivorous group of theropod dinosaurs that evolved pneumatised crania with robust, toothless jaws, apparently adapted for producing a strong bite. Using 3D retrodeformed skull models of oviraptorid oviraptorosaurians Citipati, Khaan, and Conchoraptor, along with the earliest diverging oviraptorosaurian, Incisivosaurus, we digitally reconstruct jaw adductor musculature and estimate bite force to investigate cranial function in each species. We model muscle length change during jaw opening to constrain optimal and maximum gape angles. Results demonstrate oviraptorids were capable of much stronger bite forces than herbivorous theropods among Ornithomimosauria and Therizinosauria, relative to body mass and absolutely. Increased bite forces in oviraptorid oviraptorosaurians compared to the earliest diverging oviraptorosaurian result from expanded muscular space and different cranial geometry, not changes in muscular arrangement. Estimated optimal and maximum possible gapes are much smaller than published estimates for carnivorous theropods, being more similar to the herbivorous therizinosaurian theropod Erlikosaurus and modern birds. Restrictive gape and high bite force may represent adaptation towards exploiting tough vegetation, suggesting cranial function and dietary habits differed between oviraptorids and other herbivorous theropods. Differences in the relative strength of jaw adductor muscles between co-occurring oviraptorids may be a factor in niche partitioning, alongside body size.

www.nature.com/articles/s41598-022-06910-4

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So, after learning about a bite force study on Zygophyseter, I couldn’t help but do quick and dirty calculations with them to get an idea of how hard Livyatan could bite. I basically scaled up Zygophyseter’s skull to the size of Livyatan’s to get some idea of Livyatan’s bite force.

The formula is as follows: ((Livyatan skull length/Zygophyseter skull length)^2)*bite force of Zygophyseter=bite force of Livyatan

Zygophyseter skull condylobasal length: 148 cm (Peri et al., 2021)
Livyatan skull condylobasal length: estimated 294 cm (Lambert et al., 2017)
Anterior bite force of Zygophyseter (35 degree gape): 4,812 N
Posterior bite force of Zygophyseter (35 degree gape): 10,823 N


Therefore:

((294 cm/148cm)²)*10,823 N)= ~42,709 Newtons at the posterior end
(294 cm/148 cm)²)*4,812 N)= ~18,989 Newtons at the anterior end


So, the elephant in the room: this bite force value seems woefully underwhelming. In fact, it seems very suspicious. And I agree that one of the caveats of this calculation involves using Zygophyseter as a base for Livyatan. Livyatan had a proportionately wider snout than Zygophyseter (this is obvious to anyone looking at top views of their skulls), and it wouldn't surprise me if it bit proportionally harder. Zygophyseter had a proportionally narrower snout than Basilosaurus, and this is believed to be one of the reasons why the former had a weaker bite. However, the other reason is that Basilosaurus also had a greater cross sectional area for the temporalis muscle than did Zygophyseter (Peri et al., 2021). I obviously can't quantify this, but from looks I don't know if I can say Livyatan had proportionately more area for jaw adductor muscles than Zygophyseter (compare these two images: Zygophyseter->, Livyatan->).

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Increasing morphological disparity and decreasing optimality for jaw speed and strength during the radiation of jawed vertebrates

The Siluro-Devonian adaptive radiation of jawed vertebrates, which underpins almost all living vertebrate biodiversity, is characterized by the evolutionary innovation of the lower jaw. Multiple lines of evidence have suggested that the jaw evolved from a rostral gill arch, but when the jaw took on a feeding function remains unclear. We quantified the variety of form in the earliest jaws in the fossil record from which we generated a theoretical morphospace that we then tested for functional optimality. By drawing comparisons with the real jaw data and reconstructed jaw morphologies from phylogenetically inferred ancestors, our results show that the earliest jaw shapes were optimized for fast closure and stress resistance, inferring a predatory feeding function. Jaw shapes became less optimal for these functions during the later radiation of jawed vertebrates. Thus, the evolution of jaw morphology has continually explored previously unoccupied morphospace and accumulated disparity through time, laying the foundation for diverse feeding strategies and the success of jawed vertebrates.

www.science.org/doi/10.1126/sciadv.abl3644

[theropod]

Mar 15, 2022 5:55:19 GMT 5 Infinity Blade said:

So, after learning about a bite force study on Zygophyseter, I couldn’t help but do quick and dirty calculations with them to get an idea of how hard Livyatan could bite. I basically scaled up Zygophyseter’s skull to the size of Livyatan’s to get some idea of Livyatan’s bite force.

The formula is as follows: ((Livyatan skull length/Zygophyseter skull length)^2)*bite force of Zygophyseter=bite force of Livyatan

Zygophyseter skull condylobasal length: 148 cm (Peri et al., 2021)
Livyatan skull condylobasal length: estimated 294 cm (Lambert et al., 2017)
Anterior bite force of Zygophyseter (35 degree gape): 4,812 N
Posterior bite force of Zygophyseter (35 degree gape): 10,823 N


Therefore:

((294 cm/148cm)²)*10,823 N)= ~42,709 Newtons at the posterior end
(294 cm/148 cm)²)*4,812 N)= ~18,989 Newtons at the anterior end


So, the elephant in the room: this bite force value seems woefully underwhelming. In fact, it seems very suspicious. And I agree that one of the caveats of this calculation involves using Zygophyseter as a base for Livyatan. Livyatan had a proportionately wider snout than Zygophyseter (this is obvious to anyone looking at top views of their skulls), and it wouldn't surprise me if it bit proportionally harder. Zygophyseter had a proportionally narrower snout than Basilosaurus, and this is believed to be one of the reasons why the former had a weaker bite. However, the other reason is that Basilosaurus also had a greater cross sectional area for the temporalis muscle than did Zygophyseter (Peri et al., 2021). I obviously can't quantify this, but from looks I don't know if I can say Livyatan had proportionately more area for jaw adductor muscles than Zygophyseter (compare these two images: Zygophyseter->, Livyatan->).

I think we should be scaling from skull width, since we have it and it stands to reason that a longer skull at the same skull width would actually decrease rather than increase the bite forces, and since, as Snively et al. (2015) noted, skull width has a (considerably, see Fig. 4 of that study) better correlation with bite force than skull length does, at least for mammals.

Bizygomatic width of Z. varolai is 74.5 cm, that of L. melvillei is 197 cm (Lambert et al. 2010, supplement). With Peri et al.’s bite force estimates, this gives us 33.647 and 75.678 kN for anterior and posterior biting positions respectively, figures that sound a lot more reasonable (considering the caveats inherent in the dry skull method) and more similar (still lower though) to what we get from Basilosaurus isis (Snively et al. 2015), though the anterior value I suspect may still be an underestimate, since relative to skull width the skull of Zygophyseter is 33% longer than that of Livyatan, which would likely mean it had a lower mechanical advantage at the snout tip.

EDIT: just noticed, something I had been overlooking previously, that Snively et al. actually does give us the skull width of the B. isis specimen they worked on, albeit in log-transformed form: 10^1.785, or about 61 cm.
Scaling from skull width of B. isis would thus give us a humungous 171.684 kN bite force estimate, while scaling from skull length resulted in the more modest 111.428 kN. For the posterior teeth, that is.


Lambert, O., Bianucci, G., Post, K., de Muizon, C., Salas-Gismondi, R., Urbina, M. and Reumer, J. 2010. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature 466 (7302): 105.
Peri, E., Falkingham, P.L., Collareta, A. and Bianucci, G. 2021. Biting in the Miocene seas: estimation of the bite force of the macroraptorial sperm whale Zygophyseter varolai using finite element analysis. Historical Biology: 1–12.
Snively, E., Fahlke, J.M. and Welsh, R.C. 2015. Bone-breaking bite force of Basilosaurus isis (Mammalia, Cetacea) from the late Eocene of Egypt estimated by finite element analysis. PloS one 10 (2): e0118380.

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Scaling from skull width of B. isis would thus give us a humungous 171.684 kN bite force estimate, while scaling from skull length resulted in the more modest 111.428 kN. For the posterior teeth, that is.

Does this at least seem reasonable? I can definitely see why scaling via skull width is a better way to scale bite force, just that “humongous” from your wording here makes me wonder if that’s something we should take at face value.

It’s still crazy that even posterior bite force for Livyatan calculated via scaling from skull width is still “only” within T. rex territory.

[theropod]

Probably not (or maybe at best when accounting for dry skull results being underestimates). Another basal physeteroid like Zygophyseter would definitely be a more reliable analogue than a more distantly related archaeocete. It was just for comparison's sake, and because I recall with previous attempts I only scaled using skull length because the width seemingly wasn't given (which I was mistaken about) in the paper.

Not really in T. rex territory though. Isn't the estimate for Sue with comparable (dry skull) methodology (McHenry 2009) something like 3 tons, i. e Livyatan would over twice as strong in relative terms? Currently on my phone, but I'll check later.
EDIT: McHenry (p. 491, tab. 7-7) estimated Sue’s bite force at ~17 kN (anterior) to 26kN (posterior). I think the multibody dynamics simulation from Bates and Falkingham’s study clearly produces higher estimates, as they got figures around twice as high, even for a marginally smaller T. rex skull (that of Stan).

Bates, K.T. and Falkingham, P.L. 2012. Estimating maximum bite performance in Tyrannosaurus rex using multi-body dynamics. Biology Letters 8 (4): 660–664.
McHenry, C.R. 2009. ‘Devourer of Gods’: The Palaeoecology of the Cretaceous Pliosaur Kronosaurus queenslandicus.University of Newcastle, 616pp.

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I was thinking about 3D bite force models for T. rex (especially one recent FEA that focused on juvenile tyrannosaurids). Peri et al.’s model incorporates the dry skull method and FEA, so I’m kind of on the fence on how meaningful a comparison between their data is.