Functional Morphology of Animal Feeding Apparata

[Infinity Blade]

We all know Daeodon was osteophagous, but here's some direct demonstration of it. Moropus have sometimes been found with bite marks from Daeodon. This is one specimen with bite marks on the humeral head.





If Daeodon preyed upon even male M. elatus (this is how big those could get->), then it would have been hunting pretty big prey. One of guys on a Mammalia server I'm on likened it to a Cenozoic version of theropod vs sauropod.

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This is something I voiced on Twitter recently, but I didn't get anyone's attention.

I was thinking about Smilodon populator lately. After some thought about its functional morphology and reconstructed biology, I have concluded that I don't think it was a specialist of adult megamammals >1,000 kg, and here's why.

The discovery of a >400 kg S. populator specimen led its describers to calculate a maximum prey size of nearly 3 tonnes for such a cat. This calculation is derived from equations based off of the predator's body mass. The paper states that it is well established that S. populator was specialized for hunting megaherbivores considerably larger than itself.¹

Is it though?

An even more recent study on the jaw biomechanics of saber-toothed synapsid predators found that S. populator had a total jaw gape of 82 degrees. But, and this is a big but: there's a difference between actual jaw gape and the effective gape. Because sabertooths have such long canine teeth, this inherently limits the amount of clearance between the upper and lower canines. So while S. populator was able to open its jaw joint up to 82 degrees, the effective gape (i.e. the clearance between its upper and lower canines) was actually only 32 degrees. In case anyone is wondering, S. gracilis was found to have an actual and effective jaw gape of 89 and 40 degrees, respectively, while in S. fatalis these figures turned out to be 111 and 53 degrees.²


A quick sketch I made using a protractor illustrating the actual and effective gape of S. populator.

To put this into perspective, the same study noted that most species had effective gapes ranging between 45-65 degrees, similar to that observed in modern felids. These may be the most effective jaw gapes for prey capture, but S. populator falls substantially short of them. This would limit its ability to bite into wide, girthy body parts, especially of megamammals. Below is a visual representation of what that would look like.³


(Interestingly, this study also concludes that S. fatalis was not a "megaherbivore" specialist, but rather hunting the same-sized prey relative to size as modern big cats, so what I'm preaching here isn't entirely new)

But Infinity Blade, wasn't there an isotope study that found that S. populator was eating Macrauchenia and ground sloths (Megatherium and Lestodon)?

Yes there was.⁴ But does this mean it was necessarily hunting the adults of these species? I think not. Assuming juvenile individuals were eating the same food as the adults (and I see no reason to suppose that they weren't), the isotope signatures from S. populator could have been from immature individuals as well. And juveniles, given their smaller body size, are of course easier to bite.

In a similar manner, Homotherium from Friesenhahn Cave seem to have particularly specialized on proboscideans (mammoths and mastodons), given the amount of proboscidean bones from the cave. But these weren't adult proboscideans the scimitar-toothed cats were preying upon. Rather, they targeted animals 2-4 years of age.⁵

One caveat is that the girth of body parts, especially the neck (which Smilodon is thought to target), is obviously going to vary within different prey species. Macrauchenia had a proportionately longer and more slender neck than ground sloths. So depending on the girth of an adult Macrauchenia's neck, S. populator may or may not be able to land an effective penetrating bite onto its throat. I'm pretty sure fully grown Lestodon, let alone Megatherium, are too much, at least for a single Smilodon populator.

EDIT 10/13/20: There is a preprint-> (not peer-reviewed) that reveals the diet of S. populator in Brazil. For reference, S. populator's weight was put at ~315 kg in this analysis. Next to the data are my thoughts on how effectively a solitary S. populator individual could kill an adult member of the species.

Equus neogeus (w = ~420 kg): 10%. Should be able to bite its throat.

Palaeolama major (w = ~285 kg): 14%. Could easily bite its throat.

Caiman latirostris (quick look at our profile gives w=29.2-62 kg): 10%. Could easily kill it.

Pachyarmatherium brasiliense (w = ~38 kg): 11%. Could easily kill it.

Holmesina paulacoutoi (w = ~120 kg): 12%. Could easily kill it.

Panochthus sp. (w = ~785 kg): 12%. Could kill juveniles with a skull bite; adults seem difficult to bite anywhere.

Toxodon platensis (w = ~1,770 kg): 12%. Could kill juveniles; skeptical if adults could be effectively bitten on the throat.

Catonyx cuvieri (w = ~777 kg): 10%. Depending on girth of body parts (e.g. neck), could possibly effectively bite adults.

The rest (21%) was composed of megaherbivores like Eremotherium laurillardi (w = ~3,416 kg), Notiomastodon platensis (w = ~6,265 kg), and Glyptotherium (w = ~710 kg). Interestingly, all the specimens examined in this study were adults, except for one juvenile Eremotherium specimen (perhaps a suckling individual). This juvenile's isotopic signatures were not different from the adults of the same locality, and were equivalent to mother diet, as carbon isotopic values of mother milk and offspring would not have significant differences.

What I think this suggests is that yes, isotopic signatures indicating megaherbivores in the diet of S. populator could easily have come from hunting immature specimens, even sucklings. So instead of hunting adult megamammals that it would have a hard time actually biting, it could easily overpower and land a deadly bite on much smaller juveniles. It's also possible scavenging of dead adults could produce some of the isotopic signatures.

References:

¹ Manzuetti, A., Perea, D., Jones, W., Ubilla, M., & Rinderknecht, A. (2020). An extremely large saber-tooth cat skull from Uruguay (late Pleistocene–early Holocene, Dolores Formation): body size and paleobiological implications. Alcheringa: An Australasian Journal of Palaeontology, 1-8.
² Lautenschlager, Stephan; Figueirido, Borja; Cashmore, Daniel D.; Bendel, Eva-Maria; Stubbs, Thomas L. (2020): Data table from Morphological convergence obscures functional diversity in sabre-toothed carnivores. The Royal Society. Dataset. doi.org/10.6084/m9.figshare.12950826.v1
³ Andersson, K., Norman, D., & Werdelin, L. (2011). Sabretoothed carnivores and the killing of large prey. PLoS One, 6(10), e24971.
⁴ Bocherens, H., Cotte, M., Bonini, R., Scian, D., Straccia, P., Soibelzon, L., & Prevosti, F. J. (2016). Paleobiology of sabretooth cat Smilodon populator in the Pampean Region (Buenos Aires Province, Argentina) around the Last Glacial Maximum: Insights from carbon and nitrogen stable isotopes in bone collagen. Palaeogeography, Palaeoclimatology, Palaeoecology, 449, 463-474.
⁵ chasingsabretooths.wordpress.com/2013/07/17/homotherium-slayer-of-giants/

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I knew that Thylacoleo had serrated incisors (particularly the lower ones), but what I didn't know was that the lower incisors were the real stabbing and piercing teeth. The upper incisors functioned to hold food against and to hone the lower incisors.

Also, the premolars were serrated too. Yikes.

Wells, Horton, and Rodgers, (1982) have conducted studies of the morphology and development of wear patterns on the teeth of the species Thylacoleo carnifex. They examined the striations produced by the grinding of food against the tooth enamel of known carnivores and herbivores and compared their findings with similar marks on the fossil teeth of Thylacoleo. The wear patterns created by food passing down the enamel surface of the Thylacoleo teeth were similar to those present on the teeth of known carnivores but were not like those seen on herbivore teeth. They resolved that the mandibular (lower) teeth retained a stabbing or piercing action, while the maxillary (upper) teeth functioned as both an anvil against which food is held and a "stone" against which the lowers are sharpened. Thylacoleo's large premolars have a crescent-shaped slicing edge. As these edges pass each other during a bit [sic], all the shearing forces are directed upon two converging points. This action is further emphasized by the fine serrated enamel margins of the teeth, which generate an effect similar to the cutting edge of a steak knife.

Also, wear on the maxillary incisors created a blunted, semi-circular wear surface; in contrast, wear on the mandibular incisors held a sharp triangular outline from which fine, serrated edges descended. Examination of the jaw mechanics of the complete Thylacoleo material indicates a possum-like jaw musculature designed for stabbing with the mandibular incisors and slicing with the enormous premolars. All evidence suggests a carnivorous marsupial of diprotodontid ancestry, not a plant-eater.

www.naturalworlds.org/thylacoleo/introducing/presenting/presenting_tc_2.htm

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More on Thylacoleo carnifex. While it certainly bit hard, it does not appear to have been a bone crusher. Screen captures taken from Horton & Wright (1981)->.

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New paper reconstructing bite force and jaw musculature in pterodactyloids.

academic.oup.com/zoolinnean/advance-article/doi/10.1093/zoolinnean/zlaa163/6105019?login=true

[Supercommunist]

^Related stuff:

[Infinity Blade]

Just some documentation of tooth serrations in Tylosaurus and Mosasaurus.

From Harrell & Martin (2014). A is M. hoffmanni and B is T. proriger.


The authors have this to say about the dentition of M. hoffmanni.

marginal dentition robust and long with well-developed, serrated carinae; two to five buccal facets; anterior teeth D-shaped in cross–section, becoming more elliptical posteriorly; swollen, barrel-shaped tooth roots.

All marginal teeth are posteromedially recurved and strongly bicarinate, with fine serrations that are visible to the unaided eye extending from the crown base to the apex.

An SEM was taken of the carina of one of the anterior marginal tooth crowns of TLAM NH.HR.2009.032.0001 in order to further investigate the serrations (Fig. 10A). Micrographs show that serrations are more accurately to be termed crenulations because of the irregular wavy pattern displayed. Apices of the crenulations are spaced approximately 200 μm apart. A comparison was made to a large, anterior tooth of a Tylosaurus proriger (SDSM 39968, Fig. 10B) to determine if serrations/crenulations can be used as a diagnostic tool at the generic level in mosasaurs. Preliminary results show that serrations in M. hoffmanni are larger and more irregular than those in Tylosaurus, but further analyses will be necessary to determine the usefulness of tooth serrations as a diagnostic criterion.

Massare (1987).

Most mosasaurs also have this tooth form (Fig. 12), although the amount of curvature of the tooth varies. In species of Mosasaurus, each tooth is curved backwards and inwards. In other mosasaur species, the tooth is almost straight, or only curved backwards. In Mosasaurus maximus (and perhaps all Mosasaurus species) and Prognathodon overtoni, the two carinae have transverse ribs on them, resulting in serrated cutting edges. A specimen of Tylosaurus proriger has been found with preserved stomach contents consisting of mosasaur, fish, shark, and bird fragments (Bjork, 1981). Other mosasaurs have been found with fish, belemnites, and turtle bones in their stomach region (Table 1). Thus the tooth form, tooth wear and some of the preserved stomach contents suggest that the preferred prey were large, fleshy animals such as reptiles and large fish, although the stomach contents of the mosasaurs suggest that some of these predators were capable of eating just about anything that they encountered.

Jiménez-Huidobro & Caldwell (2019) have this to say about the dentition of Tylosaurus.

Genus Tylosaurus – The results of our phylogenetic analysis support the monophyly of the subfamily Tylosaurinae (Figure 2). Character state distributions provide the following synapomorphies: (1) premaxilla predental rostrum very large and inflated (character 2 [2]); (2) premaxilla internarial bar dorsal keel present (character 6 [1]); (3) frontal olfactory canal embrasure not embraced ventrally by descending processes (character 12 [0]); (4) frontoparietal suture overlap with all three ridges almost horizontal (character 15 [1]); (5) prefrontal-postorbitofrontal overlap laterally (character 28 [1]); (6) dentary with projection anterior to first tooth present (character 57 [0]); (7) dentary anterior projection long (character 58 [1]); (8) tooth carinae with serrations (character 77 [1]); (9) vertebrae without zygosphenes and zygantra (character 78 [0]). When T. gaudryi, Ta. ‘mikasaensis’, and ‘T’. capensis are removed from the analysis, the characters that define the subfamily are the same characters obtained in the analysis using the full data set (character 2 [2], 6 [1], 12 [0], 15 [1], 28 [1], 57 [0], 58 [1], 77 [1], 78 [0]). The diagnosis of the subfamily seems to be better supported in the last analysis, when most of the missing data are excluded.

With regards to T. neumilleri.

Remarks – The preserved anatomy of materials assigned to T. neumilleri are virtually indistinguishable from similar materials described in T. saskatchewanensis and T. pembinensis, such as the similarly elongated parietal with the parietal table straight in the lateral outline (Figure 6B), a quadrate with a long suprastapedial process that reaches the midheight of the shaft, a well-developed infrastapedial process located high on the quadrate shaft (Figure 6C), posteriorly curved and labiolingually compressed teeth that are ornamented with facets and fine striations (although unflutted), and teeth that bear serrated carinae with small denticles.

I've already made a post previously in this thread about "Hainosaurus" (=Tylosaurus) bernardi.

[Infinity Blade]

The paper on Castoroides I just posted in 'Recommended literature' makes an interesting observation on the dentition of this giant beaver.

Just wanted to make a quick note here on the giant beaver's dentition.

From Plint et al. (2019):

Problematic to the latter hypothesis is that there are neither confirmed discoveries of dam or lodge structures built by giant beavers, nor substantiated evidence of Pleistocene-era cut wood that matches the occlusal surface size and angle of Castoroides incisors. The angle of protrusion of the incisors from the skull and their lack of a thin, chisel-like edge rendered giant beaver incisors ineffective tools for cutting down trees. This has not stopped speculation that masses of branches discovered in proximity to Castoroides fossils in Pleistocene sediments were built by the giant beaver. In addition, tree harvesting behaviours have been present in certain branches of the Castoridae family since the Miocene.

It appears that Castoroides did not have the same incisor morphology that allows the modern beaver to effectively gnaw wood and fell trees. Their angle and their lack of a sharp chisel-like edge adds support to the idea that they were not feeding on woody plants or gnawing trees (and by extension, building dams), in addition to the isotopic evidence presented in this paper.



It also suggests that a bite from this beaver would be no threat to an Elasmosaurus (looks at a certain thread). 🙃

[creature386]

Feb 23, 2021 3:41:08 GMT 5 Infinity Blade said:

It also suggests that a bite from this beaver would be no threat to an Elasmosaurus (looks at a certain thread). 🙃

I need to share this in... certain Discord servers.  (The post/quote, not the paper )

[Infinity Blade]

I'd love that.

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Information on albertosaurines. Proportionately, they bit just as hard as tyrannosaurines. In terms of symphysis strength, T. rex>albertosaurines>most other non-avian theropods.

The albertosaurines Albertosaurus sarcophagus and Gorgosaurus libratus are among the best represented tyrannosaurids, known from nearly complete growth series. These specimens provide an opportunity to study mandibular biomechanical properties and tooth morphology in order to infer changes in feeding behavior and bite force through ontogeny in tyrannosaurids. Mandibular force profiles reveal that the symphyseal region of albertosaurines is consistently stronger in bending than the middentary region, indicating that the anterior extremity of the jaws played an important role in prey capture and handling through ontogeny. The symphyseal region was better adapted to withstand torsional stresses than in most non-avian theropods, but not to the extent seen in Tyrannosaurus rex, suggesting that albertosaurine feeding behavior may have involved less bone crushing or perhaps relatively smaller prey than in T. rex. The constancy of these biomechanical properties at all known growth stages indicates that although albertosaurines maintained a similar feeding strategy through ontogeny, prey size/type had to change between juvenile and mature individuals. This ontogenetic dietary shift likely happened when individuals reached a mandibular length of ~58 cm, a size at which teeth shift from ziphodont to incrassate in shape and bite force begins to increase exponentially. The fact that large albertosaurines were capable of generating bite forces equivalent to similar-sized tyrannosaurines suggests that no significant differences in jaw closing musculature existed between the two clades and that the powerful bite of T. rex is the result of its large body size rather than of unique adaptations related to a specialized ecology.

cdnsciencepub.com/doi/abs/10.1139/cjes-2020-0177

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New paper focusing on juvenile tyrannosaurid jaw biomechanics. Table 6 is particularly interesting, as it compares theropod specimens and their respective jaw muscle forces.

anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.24602

[Infinity Blade]

I wanted to make some notes on Sarcosuchus.

Both species of Sarcosuchus had false ziphodont dentition, in that the teeth are carinated and have smooth crenulations on them (Souza et al., 2019).

Sarcosuchus hartti is diagnosed by the following combination of characters (autapomorphies indicated by *): false ziphodont teeth; heterodont dentition with large and tall anterior caniniforms and circular and blunt posterior teeth; smooth crenulations on both carinae; delicate longitudinal and oblique lines forming an anastomosed enamel surface*

The dentition of Sarcosuchus hartti is like that of Sarcosuchus imperator in having some degree of heterodonty, with larger caniniform-like anterior teeth and short, rounded and robust posterior teeth. Both species have carinae with well-marked anterior and posterior longitudinal ridges and smooth crenulations on them, i.e. a false ziphodont condition (sensu Prasad & de Broin, 2002). The enamel has the same pattern of delicate longitudinal lines in both species. However, S. hartti differs from S. imperator in having some additional oblique lines that form an anastomosing ornamentation on the enamel surface (Fig. 4). This is considered here as an autapomorphy of the species S. hartti. More recently, Dridi (2018) described some Sarcosuchus teeth (ONM KAM 1 and ONM KAM 2) from Tunisia with a well-distinct enamel pattern of apicobasal ridges and grooves that are different from other species.

Purussaurus is also known to have possessed pseudoziphodont teeth with false ziphodont carinae. These are analogous to the true ziphodont condition and would have helped Purussaurus puncture through prey and draw its teeth through flesh (Aureliano et al., 2015).

The teeth of Purussaurus sp. are subcircular at their base, slightly flattened at the crown, and bear pseudoziphodont ridges (sensu [55]). A gradual transition can also be seen from taller and acutely pointed anterior teeth to broader and lower posterior ones, which are more button-shaped (heterodont in shape and size). The teeth of P. neivensis have been described as curving backwards and slightly inwards [56]. Isolated teeth attributed to P. brasiliensis [19] show the same characteristics (see Fig. 5). This tooth morphology is ideal for piercing and smashing [57] and indicates a high resistance to bending forces and breakage (potentially against hard materials such as bone). On the other hand, the false ziphodont carinae, analogous to the true ziphodont morphology, assisted the teeth in puncturing and drawing through flesh [58]. All this suggests that Purussaurus were indeed predators of vertebrates. Due to the possession of stouter teeth, Purussaurus exhibited a selection towards maximizing tooth strength, also allowing in niche separation.

Souza et al. consider predation on large dinosaurs by Sarcosuchus unlikely if death rolling behavior was required for this behavior. While I agree with this assumption, the false ziphodont teeth of Sarcosuchus make me wonder if death rolling really was necessary for predation on large dinosaurs. The whole point of death rolling is to dismember the prey item, as modern crocodilians lack dentition specialized for this purpose. Since Sarcosuchus' teeth had a false ziphodont morphology that was better adapted to dismember soft tissue, it might not have needed to perform a death roll to effectively prey upon large dinosaurs.

Interestingly, the heterodont dentition of Sarcosuchus, with blunt posterior teeth, also suggests facultative durophagy as in the modern American alligator and Deinosuchus. It might have been able to prey on turtles or crush large bones.

There are some features in both Sarcosuchus species that could support other interesting behaviours. The heterodont dentition suggests a facultative durophagy, as observed among large-sized Alligatoroidea, such as Alligator mississippiensis (Daudin, 1802) and the extinct Deinosuchus riograndensis (Colbert & Bird, 1954) (Pooley, 1989; Schwimmer, 2002). In this way, Sarcosuchus could be able to prey on turtles and crush large bones of carcasses.

[Supercommunist]

On the subject of death rolling: its worth noting that false gharials will death roll, at least in self-defense:

4:42



Don't remember why they concluded sarchosuchus didn't death roll but maybe the video casts doubt on that claim.

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There was an earlier study that did a biomechanical test on the skulls of giant crocodyliforms. The results suggested that Deinosuchus and Purussaurus could perform a death roll on large dinosaurs and mammals (respectively), but Sarcosuchus couldn't.

www.tandfonline.com/doi/abs/10.1080/08912963.2014.893300

I'm not 100% sure how false gharials can handle it but Sarcosuchus apparently couldn't (I think this paper said something about scaling effects?).