Functional Morphology of Animal Feeding Apparata

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According to this recent analysis on Baurusuchus pachecoi, it had a relatively weak bite (~578 N), apparently having significantly less jaw strength than modern crocodylians of similar size. However, the authors state that a crocodylian of similar size to this specimen of B. pachecoi was a 1.5 meter long Chinese alligator, citing Erickson et al.'s 2012 crocodylian bite force paper (it, btw, had a bite force of up to 963 N at the caniniform teeth). That paper states that a Chinese alligator of a mean body length of 1.5 meters is 14 kg, which is by no means a particularly massive animal. So I wonder if part of the reason for the shockingly low bite force figure for this Baurusuchus specimen is simply due to it (possibly) being a small animal (though this would change nothing about bite force corrected for size).

www.biorxiv.org/content/10.1101/843334v1.full.pdf

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It seems obvious that the purpose of such a structure would be to aid penetration of the tooth by cutting through tissue. However, evidence has been presented to support an additional function of the carina. Freeman (1992) determined that sharp edges on the canines of some bats concentrate stress and are for the purpose of crack propagation in hard food items. These edges are positioned so as to direct a crack initiated by the canines toward the incisors and premolars, where it may be further propagated. The carinae of temnospondyl teeth are aligned mesiodistally. Thus, as the tooth penetrates a hard object and stress concentrates at the sharp edges of the carinae, any resultant cracks will be propagated toward the cracks initiated by the preceding and following teeth in the dental series, so that a complete separation of the hard object is more efficiently accomplished.

paleo.cortland.edu/globaltriassic2/Bulletin%2061%20Final/40-Rinehart%20and%20Lucas%20(Metopo%20teeth).pdf

This is interesting. Previously I've seen an experiment where a brass replica Tyrannosaurus tooth punctured bone, and cracks had propagated where the serrated carinae were, suggesting they had a role in helping crack bone. It's nice to see that this is something indeed reported by scientific literature.


14:59 to 15:43

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Tooth wear has been linked to the type of prey consumed (Caldwell and Brown 1964). A Newport Beach (California) killer whale specimen, cited in Caldwell and Brown (1964), showed extreme tooth wear (i.e., teeth worn down to the gumline) as did the 9 January 1964 specimen described above. Both were subsequently identified as the offshore haplotype (Morin et al. 2006). Two offshore killer whales that died in Barnes Lake (Southeast Alaska) also had teeth worn down to the gumline (Bain 1995). The same pattern of extensive tooth wear was reported from a mass stranding of killer whales in the Gulf of California, Mexico (Guerrero-Ruiz et al. 2006). Our photographic data also provided some interesting patterns related to offshore killer whale dentition. Resident and transient whales typically showed extensive rake marks on their dorsal fins and body made by the conical-shaped teeth of conspecifics (Ford et al. 1992, Black et al. 1997, Dahlheim et al. 1997). During our analyses of photographic data on offshore killer whales, we did not observe extensive rake markings. We did, however, see wider and shallower markings on the skin of offshore killer whales, the width of which was consistent with rake marks inflicted by teeth that had extensive wear. The causes responsible for the extreme tooth wear seen in offshore killer whales is unknown but is undoubtedly related to the type of prey being consumed. If this condition were caused by crushing bones (e.g., predating on other marine mammals), we would expect transient killer whale teeth to exhibit this condition. An examination of several North Pacific transient killer whale skulls containing teeth, available for inspection at various museums, did not find extensive tooth wear as that described above for offshore killer whales (NMML, unpublished data).

www.montereybaywhalewatch.com/pdf/OffshoreKillerWhales21305.pdf

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After looking at the Oculudentavis taxonomic controversy, I've been thinking. What are the functional consequences of having pleurodont or acrodont dentition as opposed to thecodont dentition? Only thing I can think of is that thecodont teeth seem more securely attached to the jaw bone, with a root embedded in a deep socket. What advantages, if any, would acrodont or pleurodont teeth have?

Just in case people don't know what I'm talking about, here's a visual.


Found from here->.

EDIT: I've discovered the functional consequences of having pleurodont vs acrodont dentition. Pleurodont teeth have a larger surface area of the tooth in contact with the jawbone compared to acrodont teeth, which creates a stronger attachment. At least in captive lizards with acrodont dentition, the teeth are easily lost (and unreplacable), so owners of such lizards (chameleons and agamids) are advised to be cautious when handling them.

lafeber.com/vet/understanding-reptile-dental-anatomy-clinical-applications/

I'd still imagine that the thecodont condition provides an even more secure tooth attachment than either, though, since the root is completely surrounded by jawbone. The longer the root, the harder to slip the tooth out of its socket.

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Morphology and biomechanics of the pinniped jaw.

Pinnipeds (seals, sea lions, and walruses) underwent a shift in jaw function away from typical carnivoran mastication to more novel marine behaviors during the terrestrial‐aquatic transition. Here we test the effect of aquatic prey capture and male‐male combat on the morphological evolution of a mammal jaw that does not masticate. Nine three‐dimensional landmarks were taken along the mandible for 25 species (N = 83), and corpus and symphysis external and cortical breadths for a subset of five species (N = 33). Principal components analysis was performed on size‐corrected landmark data to assess variation in overall jaw morphology across pinnipeds. Corpus breadths were input to a beam model to calculate strength properties and estimated bite force of specific species with contrasting behaviors (filter feeding, suction feeding, grip‐and‐tear feeding, and male‐male combat). Results indicate that, although phylogenetic signal in jaw shape is strong, function is also important in determining morphology. Filter feeders display an elongate symphysis and a long toothrow that may play a role in filtering krill. Grip‐and‐tear feeders have a long jaw and large estimated bite force relative to non‐biting species. However, the largest estimated bite forces were observed in males of male‐male combative species, likely due to the high selection pressure associated with male success in highly polygynous species. The suction feeding jaw is weak in biting but has a different morphology in the two suction feeding taxa. In conclusion, familial patterns of pinniped jaw shape due to phylogenetic relatedness have been modified by adaptations to specialized behavior of individual taxa.

anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.22710

Also learned this about Caviramus today.

Multiple aspects of the Caviramus jaw are of interest. It was probably a powerful biter, and perhaps regularly consumed relatively tough prey such as invertebrates with thick exoskeletons or fish with hard scales. Such a diet is indicated by its blunted and worn tooth tips, and the enamel of the anterior teeth being strongly rugose - some readers may recall from a recent article that these features also occur in other specialists of hard prey, such as the giant, turtle-eating Cretaceous crocodylian Deinosuchus. Caviramus dentition is morphologically complicated and, again, indicates some specialisation. As with many Triassic pterosaurs, the teeth are differentiated into large, curving anterior fangs at the jaw tips and complicated, multicusped teeth behind these. These posterior teeth are so numerous and tightly packed that they actually sit obliquely in the jaw, overlapping one another to form a continuous, 'megaserrated' cutting surface. The depression of the jaw joint (another atypical feature for a pterosaur, and one that won't reappear until later in pterosaur evolution) permitted these teeth to occlude simultaneously rather than gradually, as occurs in animals with jaw joints level with the toothrow. Areas of Caviramus jaw muscle attachment are large, including a broadly expanded posterior lower jaw. The mandible and skull are not, as with some pterosaurs, delicately built from slender struts but comprised of deep bars and robust bone junctions. Cross sections of the Caviramus holotype jaw indicate that some cavities were present in the cranial skeleton, but that bone volumes were superior in at least some places. This was clearly an [sic] skull capable of delivering and withstanding forceful bites, and its configuration recalls some dinosaur species which are sometimes considered to be omnivorous (e.g. many small ornithischians). Maybe it was equipped with powerful jaws so that it could tackle a wide range of tough foods, including nutritious plant matter.

markwitton-com.blogspot.com/2016/03/the-magnificent-caviramus-early-example.html

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I found data regarding jaw biomechanics for Arctotherium angustidens (Soibelzon et al. 2014; you can download the PDF on Google Scholar).

I've provided screen captures from the paper down below.



Mandibular force profiles for two specimens, particularly the relative force (Zx/Zy) was 0.83 in one specimen and 1.11 in another at the position of the canine. If I remember correctly (from what Ursus arctos from Carnivora said on the subject), the lower the value, the better the mandible is at taking stress. So these are some rather impressive strengths at the canine.

However, bite force and bite force quotient are...surprisingly low.




All these bite force estimates were via the dry skull method, so I think it's okay to directly compare these values. Despite rather high bite forces in absolute terms (even at the canine), it doesn't seem to have bitten particularly hard for its size. Absolute bite force at the canine was measured to be >1,000 N (this being a dry skull estimate, the real life value was likely greater), which sounds impressive...until you remember that the giant panda, brown bear, and the polar bear bit even harder, if anything. This is despite the fact that A. angustidens is twice as large as the polar bear, over 2.5 times larger than the brown bear, and over 5 times larger than the giant panda. Granted, the giant panda has a particularly powerful bite for its size, but the brown bear and polar bear evidently do not. So this thing had a mandible that could take far more stress than its bite force could ever reach. The extent of tooth wear seen in Arctotherium's teeth suggest a diet of tough food items like dried meat, bones, or rough plant material.

I'm not entirely sure why Arctotherium had such physically strong jaws but a relatively weak bite. I think the authors of this paper make more of a deal out of the absolute bite force than they should IMO (considering how it compares relatively speaking), but they do mention the hunting methods of the modern spectacled bear (the only living member of the Tremarctinae) against large prey. This bear ambushes the prey, immobilizes it with the forelimbs, and eats it alive by starting at the back; the prey dies from shock and stress. Alternatively, the bear chases the prey item through rough terrain, hillsides, or precipices, prompting it to fall possibly to its death. The authors suggest that giant short-faced bears like Arctotherium could have used the same strategies. Intuitively, I would guess that's possible; eating prey alive after immobilization might not need a relatively strong bite (although, T. ornatus has a vastly superior BFQ than A. angustidens, especially at the canines), and provoking it to fall to its death certainly doesn't.

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Interesting theory, maybe this could be how short-faced bears in general hunted.

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Probably something we all knew, but I learned this college semester that human canines have been deemed incisiform before, which was interesting.

Neither is there any correlation with diet. Although paranthropes developed an increasingly impressive masticatory apparatus, with a small incisor-canine arch and very large, strong premolars and molars, the reverse trend is true of Homo, in whom the incisor-canine arch is expanding as the premolars and molars tend to regress. Paranthropes and humans are both omnivores, but our relatives can chew huge quantities of tough plant material, especially roots, while most humans include a considerable amount of meat in their diets, although we still subsist primarily on fruits and vegetables. It is incorrect to claim that the human canine is linked to the consumption of meat, because all hominids, as well as modern chimpanzees, eat meat regularly. Thanks to increasingly incisor-like morphology and its powerful root, the human canine tooth tears flesh very effectively. But, as we have seen, neither carnivores nor apes ever employ their canines for alimentary purposes. And it is also true that no adaption of the human canine to tear flesh was necessary, because our earliest cave man ancestors could do this with their razor-sharp stone tools. We can consider this to be secondary “pseudo-adaptation”; in other words, the human canine has not become incisiform in order to eat meat, but has found a secondary application in doing it.

www.jdao-journal.org/articles/odfen/pdf/2010/01/odfen2010131p4.pdf

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This is mostly a paper about detecting sexual dimorphism, but it makes comments regarding the relative snout length and width of large male gharials, as well as relative tooth size.

Finally, we note that the largest narial fossae are associated with an increase in the size of the terminal rosette and a broadening of the snout (increased minimum width), and this may increase the ability of males to catch larger prey. Although we did not measure tooth size across all specimens, we note that some of the largest males (e.g. Grant Museum—LDUCZ X215) apparently have disproportionately large teeth compared to smaller animals, and this would likely allow them to tackle larger prey than may be expected. Given the great differences in size between osteologically mature gharials and young juveniles, there would be niche partitioning between various different growth stages, as seen in other crocodylians (Dodson, 1975). However, there may also be separation between larger (and presumably fitter) gharial males and other adult animals, and if so, this may also be a very important consideration for sustaining populations. If high-quality males are removed from a population, this has the potential for profoundly negative effects in small populations (Knell & Martínez-Ruiz, 2017). So if our hypothesis about prey preference is correct, suitable prey for larger males must be a consideration in establishing suitable habitats for sustainable gharial populations or they may be at risk.

peerj.com/articles/9134/#supp-1

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Mar 12, 2020 7:33:45 GMT 5 Infinity Blade said:

According to this recent analysis on Baurusuchus pachecoi, it had a relatively weak bite (~578 N), apparently having significantly less jaw strength than modern crocodylians of similar size. However, the authors state that a crocodylian of similar size to this specimen of B. pachecoi was a 1.5 meter long Chinese alligator, citing Erickson et al.'s 2012 crocodylian bite force paper (it, btw, had a bite force of up to 963 N at the caniniform teeth). That paper states that a Chinese alligator of a mean body length of 1.5 meters is 14 kg, which is by no means a particularly massive animal. So I wonder if part of the reason for the shockingly low bite force figure for this Baurusuchus specimen is simply due to it (possibly) being a small animal (though this would change nothing about bite force corrected for size).

www.biorxiv.org/content/10.1101/843334v1.full.pdf

Since they specifically mention the size of the chinese alligator, I'm rather curious as to why they omitted a few species in their comparison here. The freshwater crocodile, yacare caiman, and dwarf caimans all have rather comparable body sizes in the sample groups.

The Yacare caiman (C.yacare) sample was only ~4kg heavier than the chinese alligator group, and the spectacled caiman (C.crocodilus) sample group was only ~6kg heavier.

Paleosuchus palpebrosus was very similar in body mass to the mean Chinese alligator BMB (-1kg), and the Trigonatus sample was a good deal (~8kg) heavier.

The freshwater crocodile (C.johnstoni) group had a mean body mass ~6kg heavier than the chinese alligator. I know that it is a slender snouted species and not really known for a bite force of impressive dimensions, but this is merely to emphasis the size demographic.

Below is a screenshot of Erickson's results with the above species highlighted to show an emphasis. Since their is a specific emphasis in Caniform bite force, i've highlighted that column as well.




I'm not exactly sure how big B.pachecoi is, but i think including multiple species in the comparison, and not just singularly the chinese alligator, gives a broader and probably better idea about comparisons with smaller crocodilians. This all being said, i think the conclusion on feeding ecology they made is perfectly reasonable. 

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Interesting. I definitely agree that multiple species for comparison is better; now I suppose that the only thing that needs to be worked out is exactly how big B. pachecoi is.

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Cyonasua and Chapalmalania are the only South American carnivorans currently known to overlap sparassodonts in time and may have been the only terrestrial carnivorans to directly interact with them. It has been suggested that significant competitive interaction may have occurred between Cyonasua-group procyonids and some sparassodonts, particularly the genus Stylocynus (Marshall 1977; Soibelzon 2011; Prevosti et al. 2013; Engelman and Croft 2014), due to similar habits and these animals overlapping in time. Cyonasua and Chapalmalania are positioned very far from the morphospace occupied by South America metatherians (Didelphimorphia and Sparassodonta), which suggests little to no ecological overlap with these groups (Fig. 1), in agreement with most previous studies. Although the degree to which sparassodonts were omnivorous has been debated (Marshall 1977; Prevosti et al. 2013; Croft et al. 2018), virtually all authors agree that no South American metatherian (sparassodont or didelphimorphian), with the possible exception of Stylocynus, was as omnivorous as extant procyonids or ursids. However, even Stylocynus plots outside the hypocarnivore morphospace occupied by Ailurus, procyonids, and ursids (as well as Cyonasua-group procyonids), closer to mesocarnivorous or even hypercarnivorous taxa such as Canis lupus, Chrysocyon brachyurus, and Spilogale spp. Prevosti et al. (2013) considered Stylocynus to be hypocarnivorous based on relative grinding area but did not exclude the possibility of a mesocarnivorous diet. The results of this analysis and Croft et al. (2018) support the idea of a more mesocarnivorous diet for Stylocynus.

The hypothesis that ecological dissimilarity played a role in the early colonization of South America by Cyonasua-group procyonids is supported by comparing the position of procyonids in the results of the CA to canids, ictonychine (= galictine) mustelids, and the mustelid Eira, three groups that likely had dispersal abilities similar to those of procyonids but did not disperse to South America until much later, after the last record of sparassodonts. Canids and ictonychines in particular are the earliest known carnivorans in South America aside from Cyonasua-group procyonids (with the earliest records dating to ∼2.9 Ma; Prevosti and Forasiepi 2018) and are some of the few groups of carnivorans known to make successful dispersals over water (van der Geer et al. 2011). Procyonids plot outside sparassodont morphospace; whereas canids, ictonychines, and Eira plot within sparassodont morphospace, as would be expected if ecological dissimilarity was a factor in successful colonization.

Engelman & Croft (2019)

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This is from a newly published paper about the dental anatomy of Sinraptor dongi (Hendrickx et al., 2020).

If the dentition of Sinraptor dongi is obviously adapted for a carnivorous diet, several features suggest that its teeth were suited for a predatory lifestyle. Similar to those of abelisaurids and tyrannosaurids, the mesial teeth of Sinraptor dongi and Allosaurus are mesiodistally thick and were able to endure high mechanical stresses (Hendrickx et al. 2019). Robust mesial dentition appears to be adapted towards diets involving bone crunching and bone biting, with high degrees of torsion applied on mesial teeth (Reichel 2010, 2012). Such a mesial dentition was suited for gripping and pulling on prey in a bite-and-hold manner (Sampson and Witmer 2007; Reichel 2012). If mesial teeth with lingually deflected carinae and D- and U-shaped cross sections are perfectly suited for defleshing carcasses (Reichel 2012), the wide distances between mesial and distal carinae in mesial teeth, associated with spiralling mesial carinae and deflected distal carinae in anterior lateral teeth, would make wide cuts, keeping the wounds open and ultimately causing fatal injuries to the prey (Bakker 1998; Reichel 2012; Hendrickx et al. 2019). Additional evidence supports Sinraptor dongi as a predator. The large number of partially healed bite wounds seen on the cranial material of Sinraptor dongi (i.e., 28 tooth strike lesions distributed on the maxilla, jugal, dentary, prearticular, and possibly the surangular; Tanke and Currie 1998; Fig. 2B) was interpreted by Tanke and Currie (1998) to be indicative of aggressive inter- or intraspecific biting. Because Sinraptor dongi appears to be the only large-bodied theropod from the upper beds of the Shishugou Formation, intraspecific head- and face-biting behaviour most likely occurred in this taxon. If true, this supports the fact that the dentition of Sinraptor dongi was capable of enduring tooth-to-bone contact and was consequently well suited to a predatory lifestyle. Indeed, extensive spalled surfaces on the crown apices, which reflect flaking of enamel caused by the contact between the crown and food (Schubert and Ungar 2005), combined with fully worn apices in some mesial and lateral teeth, clearly indicate particularly high forces produced during contact with what was most likely the bones of prey items. Sinraptor dongi, together with Allosaurus, have been hypothesized to be “strike-and-tear/pull feeders”, rapidly striking downwards at smaller prey using the mesial dentition (Snively and Russell 2007). Neck muscle morphologies in Sinraptor dongi and Allosaurus correlate with powerful ventroflexise kinematics, which would facilitate cutting flesh with the upper dentition (Snively and Russell 2007). Allosaurus, whose dentition is very similar to that of Sinraptor dongi, is widely regarded as a predator on the basis of the discovery of a Stegosaurus cervical plate with a bite pattern matching that of Allosaurus, and an Allosaurus caudal vertebra showing a partially healed wound likely caused by a Stegosaurus tail spike (Carpenter et al. 2005). Consequently, Sinraptor dongi is here interpreted as a predator, likely having preyed on medium-sized herbivorous dinosaurs such as the stegosaurid Jiangjunosaurus junggarensis, using its dentition to inflict fatal injuries in a manner similar to that of Allosaurus.

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The evolution of the elephantid jaw from a gomphothere-like condition (with an elongate mandibular symphysis and lower tusks) to the condition we're more familiar with today.


Cenozoic Mammals of Africa->

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Some information on Carnotaurus, and abelisaurids in general.

Sampson and Witmer (2007) described in detail the enhanced mineralisation in abelisaurid cephalic soft tissues mainly focused on Majungasaurus anatomy. The suite of characters includes diverse patterns of dermal sculpturing and complex bone articulations (although see Hieronymus 2009, for a complete discussion of the sculpturing correlates). Based on these previous works, it is evident that Carnotaurus shared these complex articulations and different sculpturing patterns on the cranial bones. The massive frontal horns were probably covered by a cornified sheath (Hieronymus et al. 2009). Other heavily ornamented bones correspond to the nasals and the dorsal areas of the premaxilla, lacrimal and postorbital. The projected rugosities, as well as the intense pitting and some raised edges, likely correspond to a cornified pad covering (Hieronymus 2009; Delcourt 2018).

Carnotaurus, as well as most abelisaurids (e.g. Abelisaurus; Skorpiovenator; Arcovenator; Majungasaurus) shows postorbital and lacrimal bones with strongly developed dermal projections which almost encloses the orbit. Besides these dermal outgrowths, the mineralisation of the suborbital ligament would have delimited the ventral orbital sector (Chure 1998; Sampson and Witmer 2007). These broad and rough circumorbital bones stands in contrast with the gracile and mostly smooth bones of the basal ceratosaurs Ceratosaurus, Eoabelisaurus and noasaurids (e.g. Masiakasaurus; Carrano et al. 2011). As previously indicated by Sampson and Witmer (2007), abelisaurids maybe had a propensity to mineralise cranial systems; Carnotaurus, as well as Majungasaurus, have an ossified interorbital septum and ethmoidal complex (Paulina-Carabajal 2011a; Paulina-Carabajal 2011b). Further, the calcification of the hyoid bones (ceratobranchials and basihyal) seems to have been influenced by this hypermineralization; these elements usually remain cartilaginous in extant archosaurs, and probably, most dinosaurs. Although the hypermineralization of the skull soft tissues is an abelisaurid feature, it was convergently acquired by carcharodontosaurids and tyrannosaurids (Novas 1997; Holtz 2004), suggesting a propensity on the hypermineralization in many mid- and large-sized theropods. The pattern of highly sculptured cranial bones in concert with the thick and strong skulls, would have diminished tensions during the bite (Henderson 2002; Rayfield 2004); and as proposed for the case of circumorbital bones, it would have protected the eye against eventual blows resulting from intraspecific competition (Hieronymus 2009; Novas 2009).

This recent paper later states that:

In sum, the strong mineralization of most skull roof and circumorbital bones, coupled with coossification of several bone joints, suggest that Carnotaurus lacks cranial kinesis, or at least, it was not as kinetic as was proposed previously by Mazzetta et al. (1998). This supports the results of Sampson and Witmer (2007) for these cranial bones, while a plausible kinesis is restricted to the intramandibular joint.

And even the intramandibular joint was not extremely weak as previously stated.

Although the articulation between dentary and postdentary bones was early described as ‘extremely weak’ (Bonaparte et al. 1990), it should be instead better described as a looser articulation (in terms of ossification) that resulted in a more mobile joint.

drive.google.com/file/d/1wVOlX-NR7DcpV2Ty0AiRVRZwbBMWl0bY/view


EDIT: more information on the family as a whole.

Biomechanical studies on the skull of abelisaurids have suggested that they had cranial mechanical advantage similar to allosaurs (e.g. Allosaurus fragilis and Carcharodontosaurus saharicus) and similar bite force (e.g. Carnotaurus: 3,341 Newtons; Allosaurus: 3,573 Newtons). These results mean that these two groups had high efficient mechanical advantage, but a bite force not as strong as that of Tyrannosaurus.

According to the analyses of Therrien et al., carnotaurines (e.g. Majungasaurus and Carnotaurus) might have been ambush predators attacking large prey. Additionally, Sampson and Witmer have suggested that Majungasaurus, and possibly other carnotaurines, were “adapted for a mode of predation that entailed relatively few, penetrating bites accompanied by powerful neck retraction, as well as bite-and-hold behaviour”. This predatory behaviour is consistent with results on skull biomechanics as well as neck analyses.

The development of advantageous features (e.g. large muscles for cursorial abilities) plus the increase the body size towards the phylogeny granted abelisaurids the opportunity to succeed the carcharodontosaurids as main predators in the Southern Hemisphere after their extinction in Turonian. Interestingly, these two groups share dentary and skull advantage mechanics that might have helped the extinction of carcharodontosaurids through ecological interactions1 when this group was becoming rare in the Cenomanian, possibly due to climate changes (i.e. changing in the mean temperatures and floral compositions)79. Therefore, it is reasonable to suggest that the latest abelisaurids (carnotaurine) were tyrannoasaurid counterparts since the former were dominant in Southern Hemisphere and the latter in Northern Hemisphere.

www.nature.com/articles/s41598-018-28154-x