Did authentic mega-killers keep their mouths shut?

The extinct Smilodon (https://en.wikipedia.org/wiki/Smilodon), largest-bodied of all sabretooth Felidae, belongs to an extinct subfamily, Machairodontinae.

Smilodon is particularly well-known because of the unusually large number of skeletons excavated. More than 1200 specimens have been recovered at the La Brea Tar Pits of California (https://en.wikipedia.org/wiki/La_Brea_Tar_Pits), where the species is Smilodon fatalis (https://mobile.twitter.com/PalaeoSD/status/1097344089647915008/photo/2 and https://prehistoric-fauna.com/Smilodon-fatalis-hunt and https://prehistoric-fauna.com/Smilodon-fatalis-hunt and https://www.flickr.com/photos/jsjgeology/15443009192).

The South American species Smilodon populator (https://prehistoric-fauna.com/Smilodon-populator-family and https://prehistoric-fauna.com/Smilodon-populator and https://prehistoric-fauna.com/Smilodon-populator-2008 and https://prehistoric-fauna.com/Smilodon-populator-family and https://prehistoric-fauna.com/Smilodon-populator-rec), largest-bodied of all recorded species of felids, is also fairly well-documented skeletally.

This genus has repeatedly been depicted fang-baring in a way similar to the leopard (Panthera pardus, https://www.agefotostock.com/age/en/details-photo/snarling-leopard-with-huge-teeth/ESY-017555797) but with the mouth even more widely open. The latest artistic reconstructions of Smilodon, particularly by Roman Uchytel (https://prehistoric-fauna.com/), are impressively realistic in most respects.

But does a snarling expression in confrontation with other species seem in line with all the known facts?

I suggest that the answer is no.

Fang-baring varies greatly in extant Carnivora. For example:

In the case of sabretooth felids in the genus Smilodon, there are three main reasons to doubt that fang-baring occurred at all, let alone in warnings to other species.

Firstly, it is unlikely that the canines were used in self-defence against other predators. Smilodon fatalis in North America did coexist with Panthera atrox (https://phys.org/news/2010-05-scientists-american-lion.html) and large-bodied species of wolves and bears, all of which could potentially overpower it. However, the exceptionally massive Smilodon populator of South America outweighed any sympatric carnivore.

Secondly, the long canines were extremely specialised for particular techniques of killing massive prey. These teeth seem too cumbersome and too fragile for rapid snapping or stabbing. Indeed they were probably a liability rather than an asset in fighting.

Thirdly, the main weapons used by Smilodon, in fights with conspecifics and other Carnivora, were probably the self-sharpening claws. The retractable claws of Smilodon, albeit extremely large on the massive forefeet, were otherwise typical of felids (see footnote 2 below).

And fourthly, a main function of fang-baring in felids is to show that, in the individual concerned, the canines remain intact (in full length and sharpness). In extant Carnivora, baring is necessary because the upper canines are normally hidden by the upper lips.

Because the canines projected permanently from the lips in sabretooth felids, such display seems pointless, whether directed intra- or interspecifically. Why would a felid flaunt the obvious?

The continued depiction of fang-baring in even the best reconstructions of Smilodon thus seems pseudo-scientific and superfluous. It suggests a subconscious appeal based on emotion at the expense of scientific accuracy.

In future, would it not be more realistic – if less dramatic – to portray Smilodon keeping its mouth closed in aggressive and defensive postures?   
 
Footnote 1: SMALL LOWER CANINES IN SMILODON

The lower canines tend to be overshadowed by the upper canines. It is therefore easy to overlook the fact that the lower canines of Smilodon are actually far smaller than expected for felids.
 
The lower canines in Panthera, exemplified by the jaguar (Panthera onca) in the photo-comparison below, are used to brace the upper canines and the third upper incisors in a clamp-like bite (https://wildfact.com/forum/topic-modern-weights-and-measurements-of-jaguars?page=2). By contrast, there is obviously no such clamping possible in sabretooth felids. This is presumably why the lower canines of Smilodon are as remarkably small as the upper canines are remarkably large.
 
Whereas the jaguar and the leopard fang-bare with an open mouth partly to show the lower canines (as well as the upper canines), it would be pointless for Smilodon to do so. Not only are the upper canines fully exposed when the mouth is closed, but to fang-bare the lower canines would be equally pointless because these teeth are unimpressive.
   
The following photos of the skull of Smilodon shows that the lower canine is no larger than the third upper incisor, located medial to it and immediately adjacent when the mouth is closed.

Smilodon  
http://www.boneclones.com/images/bc-067t-lg.jpg

http://www.boneclones.com/images/bc-018t-lg.jpg
 
In contrast, the following photos of the skull of the jaguar shows that the lower canine is nearly as impressive as the upper canine, and far larger than the third upper incisor.
 
Panthera onca
https://www.flickr.com/photos/mateov2/2858831130

https://wakingupwild.com/photography/guides-feathers-skulls-artifacts/animal-skull-identification-guide/jaguar-5/

https://fineartamerica.com/featured/jaguar-skull-gregory-g-dimijian-md.html
   
Note the way the carnassial overlaps its counterpart on the lower jaw, showing the ‘hyper-occlusion’ necessary to slice through hides of megaherbivores.
 
Smilodon
https://c1.staticflickr.com/3/2791/4152665646_11f6e6efa2.jpg
  
Footnote 2: PROTRACTILE TOE-TIPS IN CARNIVORA AND SHARP HIND CLAWS IN SMILODON

See https://www.reddit.com/r/Naturewasmetal/comments/70ow38/smilodon_populator_claw_size_comparison_with/
 
Everyone knows that felids other than the cheetah (Acinonyx jubatus) have protractile toe-tips (usually called ‘rectractable claws’).

However, the incidence of sharp claws on the hind feet of Smilodon is food for thought.
 
There is no puzzle in the case of the forelimbs. It makes perfect sense that the foreclaws are used in securing prey, and they need to be kept sharp in digitigrade animals such as felids.
 
However, in the case of the hindlimbs, the function of sharp claws is somewhat ambivalent. In the case of the larger-bodied felids, which hardly climb trees, the presence of protractile toe-tips on the hindfeet is perhaps surprising.
 
Virtually all extant species of felids other than the cheetah can climb vertically up tree trunks, partly by means of the sharp hind claws. However, a problem is in returning. Even a felid as small as the domestic cat can get stranded up a tree because a combination of digitigrade foot-form and sharp claws is ill-suited to descending headfirst. The felid has to descend tail-first, or else jump to the ground.

Above a certain height and on trees with smooth bark, any felid more than a certain body mass can find itself in a predicament after climbing. This may help to explain, for example, why the tiger (Panthera tigris) seldom climbs despite being capable of ascending.
 
Adults of Smilodon, being more massive even than the tiger, probably seldom climbed. As top predators, they had few enemies to escape from. At any height above a few metres, Smilodon would risk injury in its descent.
 
If so, why have protractile toe-tips on the hindlimbs at all?
 
The following photos confirm that, in Smilodon, the hind toes were similar to the fore toes in possessing the sheaths that protect ‘retractile claws’.

http://upload.wikimedia.org/wikipedia/commons/7/7a/Smilodon_californicus.jpg

https://en.m.wikipedia.org/wiki/File:Smilodon_skeleton.jpg

http://upload.wikimedia.org/wikipedia/commons/c/c9/Smilodon_populator_Dientes_de_Sable.jpg

Non-felid Carnivora with protractile toe-tips on the hindlimbs use the sharp hindclaws for descending trees, by virtue of the ankle being flexible enough to bend so far backwards that the animal can hang from its hind feet on the bole. This applies to forms as diverse as fossa (Cryptoprocta), ringtail/cacomistle (Bassariscus), various viverrids including the binturong (Arctitis), the semi-amphibious otter civet (Cynogale), and Asiatic linsangs (Prionodon).

In at least three species of felids, namely the margay (Leopardus wiedii) and clouded leopards (Neofelis spp.), the ankle joint is similarly flexible, allowing headfirst descent.
 
Assuming that Smilodon did not possess sufficiently flexible ankles to descend trees safely, the main use for its sharp hind claws may have been in securing prey. Its forelimbs were disproportionately large, even more so than in the tiger (which has somewhat weak-looking hindlimbs). Is it possible that Smilodon was unusual among large-bodied felids in the degree to which the subduing of prey depended on the sharp hind claws?
 
Footnote 3: SEXUAL DIMORPHISM IN SMILODON

Did sexual selection contribute to the size of the canine teeth of Smilodon? The answer seems to be no.
 
As shown below, Smilodon seems to have been less sexually dimorphic than the modern lion (Panthera leo). And there seems to be no sexual dimorphism in its canines beyond proportionality with the somewhat greater absolute body size of mature males than of adult females.
    
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2009.00659.x/abstract

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0048352
 
http://en.wikipedia.org/wiki/Smilodon

If the form of the canines in Smilodon is unexplained by any sexual factor, fang-baring (or the lack thereof) would presumably have been similar in females and males.
 
 Footnote 4: BODY MASS OF SMILODON

Smilodon populator of South America had a height at the withers of about 1.2 m. Its average adult body mass was surely more than 250kg, making it heavier than any extant species of felid. The extant lion has body mass of adult females about 120 kg and mature males about 180 kg (with extremely large-bodied individuals reaching 250 kg). Because Smilodon was not as sexually dimorphic as the lion, adult females of S. populator were probably twice as massive as adult females of the lion.

It seems reasonable to assume that Smilodon populator probably had body mass of about 250kg (adult females) and about 300kg (adult males).

One way to envision this body size is by means of a particular living individual of the liger (hybrid: male lion X female tiger, https://en.wikipedia.org/wiki/Liger). 'Hercules', pictured below, has a height at the withers of 1.25 m and a body mass up to 418 kg. It is in fat condition, so a wild individual of this height might have body mass of only 300kg.
 
Based on the above: the individual liger pictured below, i.e. Hercules, is indeed suggestive of the size of S. populator relative to the average human figure (https://en.wikipedia.org/wiki/Smilodon#/media/File:Wiki_Smilodon_Size.svg). 
 
Hercules the liger, with withers height of 1.25 m
http://ispyanimals.files.wordpress.com/2011/03/lion-tiger-05.jpg?w=450&h=321

Also see https://www.youtube.com/watch?v=JE8Z5Es-M0E and https://www.patriotledger.com/story/entertainment/local/2010/09/04/hercules-leads-pack-big-cats/1431568007/ and https://www.thehindubusinessline.com/news/world/hercules-giant-10-feet-liger-sets-guinness-world-record/article20661698.ece1 and https://www.ligerworld.com/liger-deformity-myth-reality.html and https://ourplnt.com/worlds-largest-living-cat-hercules-liger-video/ and https://www.reckontalk.com/worlds-largest-cat-liger-hercules-lion-tiger-fact-photo/.

Publicado el mayo 29, 2022 07:08 MAÑANA por milewski milewski

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