Does the colouration of the giant panda hint of anti-predator defence by means of mutilating premolars? part 1

(For a concise version please see https://www.inaturalist.org/journal/milewski/66782-why-is-the-giant-panda-black-and-white-concise-version#)

Why is the giant panda (Ailuropoda melanoleuca, https://www.inaturalist.org/taxa/41659-Ailuropoda-melanoleuca) so boldly black and white? Why - in contrast to other bears - is its colouration so consistent, i.e. lacking individual variation? And why does it tend to be so unexpressive?

(The main function of the checker-like pattern of the giant panda is unlikely to be camouflage in a patchily snow-covered landscape, as a few authors have previously suggested.)

Could this plausibly be an example of warning colouration? Indeed, is it possible that the giant panda is the largest-bodied carnivore that possesses aposematic colouration at the scale of the whole body?

The most dangerous predators - apart from humans - historically affecting the giant panda were the tiger (Panthera tigris amoyensis, https://www.inaturalist.org/taxa/41967-Panthera-tigris) and the dhole (Cuon alpinus hesperius/lepturus, https://www.inaturalist.org/taxa/42101-Cuon-alpinus), with the leopard (Panthera pardus delacouri/japonensis, https://www.inaturalist.org/taxa/41963-Panthera-pardus) and the snow leopard (Panthera uncia uncioides, https://www.inaturalist.org/taxa/74831-Panthera-uncia) also playing a part.

The giant panda was in all likelihood vulnerable to predation because of its noisy eating habits and relatively slow reproduction.

All members of the Carnivora defend themselves with their teeth, and many show their teeth to would-be attackers.

However, the giant panda seldom adopts a fang-baring expression or even opens its mouth in fear/anger.

Furthermore,

What seems to have been overlooked about the giant panda is that its premolars are unique among carnivores in their shape and arrangement (https://animaldiversity.org/accounts/Vertebrata/specimens/collections/contributors/skulls/ailuropoda/a._melanoleuca/panda_ltr/?f=subject::specimen::teeth::lower%20tooth%20row and https://commons.wikimedia.org/wiki/File:Animaldentition_ailuropodamelanoleuca.png).

Also see https://upload.wikimedia.org/wikipedia/commons/4/45/Giant_Panda_Skull.JPG and https://boneclones.com/product/giant-panda-skull-adult-BC-324 and https://www.skeletonsandskullssuperstore.com/product/giant-panda-female-skull/). These premolars may not look intimidating (https://www.alamy.com/closeup-of-giant-panda-s-mouth-and-teeth-wolong-nature-reserve-sichuan-image106119.html), but would-be predators would be wise to beware.

The giant panda has the most powerful bite of any extant species of bear (https://www.researchgate.net/publication/224630206_Finite_Element_Analysis_of_ursid_cranial_mechanics_and_the_prediction_of_feeding_behaviour_in_the_extinct_giant_Agriotherium_africanum_the_bare_facts and https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/j.1469-7998.2011.00862.x). The bite is powerful even at the premolars, because

See https://phys.org/news/2021-07-evolution-giant-panda-temporomandibular-joint.html and https://news.cgtn.com/news/3d3d674d7763444d32457a6333566d54/index.html and https://www.researchgate.net/figure/Adaptive-morphological-characteristics-of-giant-pandas-A-pseudothumb-denoted-by-the_fig1_266570673.

The giant panda has the shortest face of all bears. Ironically, the same short muzzle that makes the giant panda rather appealing as a 'human face' also houses its main weaponry.

The compact dentition of the giant panda can best be illustrated in contrast with the polar bear, the species most specialised for carnivory. Compare https://www.mindenpictures.com/stock-photo-giant-panda-ailuropoda-melanoleuca-skull-adult-length-mm-naturephotography-image80161382.html and https://www.zoochat.com/community/media/skull-giant-panda.469645/ with https://beautifullybony.wordpress.com/archive/bone-of-the-month/the-polar-bear/the-skull-biomechanics-of-the-polar-bear/ and http://digimorph.org/specimens/Ursus_maritimus/male/ and https://www.westend61.de/en/imageView/MW000023/skull-of-polar-bear-ursus-maritimus-in-front-of-black-background-side-view and https://www.acornnaturalists.com/bear-polar-skull-replica.html.

Among living bears, it is the least carnivorous species, i.e. the giant panda, that has

  • the strongest bite, and
  • the largest premolars.

An adaptive reason for the powerful bite at the level of the premolars may be an ability to slice bamboo, preparatory to grinding it with the molars (https://www.researchgate.net/figure/Segmented-maxillary-teeth-of-the-living-bear-species-analysed-in-this-article_fig3_328232826 and https://www.natureinstock.com/search/preview/giant-panda-ailuropoda-melanoleuca-skull-adult-close-up-of-molar/0_11300923.html and https://animaldiversity.org/accounts/Carnivora/specimens/collections/contributors/skulls/ailuropoda/a._melanoleuca/panda_lm/). This woody form of grass is the staple diet of the giant panda.

In particular, premolars 2 and 3 on the upper jaw, and 2, 3 and 4 on the lower jaw, form a tightly occluding set, operating by means of powerful jaw-muscles. (I have described these teeth in detail in the comments below.)

Although the dentition of the giant panda may be adaptive primarily to its diet, the same premolars are 'mutilars', capable of mutilating any animal attacking the giant panda. This is in conjunction with clamping by the jaws and hugging with the forelegs - in contrast to the piercing bite-and-release and scratching inflicted by felids.

The key to understanding the individually consistent black-and-white pattern of the giant panda as warning colouration may be to realise that the bamboo-crushing premolars of this species are quasi-carnassials, and that they are

  • even more dangerous than the canines of most other carnivores, but
  • intrinsically difficult to display directly as dangerous.

According to this explanation, the giant panda has evolved true aposematic whole-body colouration as a way of announcing its hidden defensive capability.

In its strict sense, 'aposematic' refers to warning colouration in those organisms in which the defensive capabilities are not only extraordinary and specialised, but also non-apparent as such.

If the giant panda really is aposematic at the scale of the whole body, then it may possibly be the largest-bodied aposematic organism on Earth.

How do the patterns of dark/pale contrast differ between the giant panda and other bears?

I will discuss the eyes and ears in part 2. However, in the case of the chest, other species of bears show certain trends in colouration that can be extrapolated to the extremes shown in the giant panda.

More than any other family of carnivores, bears express two patterns consistently:

  • all bears except for the brown bear (Ursus arctos) tend to be conspicuously dark or pale overall, and
  • in the dark species there tend to be conspicuously pale marking in various configurations on the chest, exposed when the animal rears up in confrontation, and possibly functioning as warning signs.

The giant panda is odd in having large patches of black on an otherwise whitish coat. Other bears tend to have either dark or pale (i.e. polar bear (Ursus maritimus) and pale morph of American black bear (Ursus americanus) tones dominant, without gross variegation. And no predominantly pale bear has dark markings on its fur.

The retention of brownish on its posterior (https://www.istockphoto.com/photo/the-giant-panda-or-bamboo-bear-gm601399942-103438177 and https://www.shutterstock.com/nb/video/clip-1021033759-giant-panda-ailuropoda-melanoleuca-rubbing-tail-against and https://www.shutterstock.com/nb/video/clip-32900209-panda-forest and https://pandathings.com/learn-about-the-giant-panda/do-pandas-have-tails/) suggests that the giant panda is not unique among bears, just extreme in its differentiation into dark versus pale.

An explanation for the relatively plain coats of other bears is that these formidable and non-gregarious mammals, all of which rely on smell and none of which hunts by stealth, need neither cryptic colouration nor social colouration that advertises sex, age, or maturity.

The dark chest of the giant panda is unusual among bears in lacking the ominous 'pectoral flags' seen in the sloth bear, Asian black bear, and sun bear, in upright confrontation (https://www.reddit.com/r/NatureIsFuckingLit/comments/ogont1/sloth_bear_stands_its_ground_against_a_tiger_india/ and https://en.wikipedia.org/wiki/Asian_black_bear#/media/File:Ursus_thibetanus_3_(Wroclaw_zoo).JPG and https://www.bigstockphoto.com/image-330810433/stock-photo-asiatic-black-bear-standing-and-relax-in-the-summer-black-bear-with-chest-the-v-shape-is-white-woo and http://www.bearsoftheworld.net/sun_bears.asp and https://www.alamy.com/stock-photo-a-sun-bear-helarctos-malayanus-standing-up-on-it-hind-legs-at-rare-89813043.html).

Although the giant panda seems to differ categorically from other bears of similar body size in this way, an alternative interpretation is that it has effectively expanded the insignia on chest and face to convert the whole front to black-and-white (http://www.ecns.cn/m/visual/hd/2018/01-14/151448.shtml and http://www.china.org.cn/environment/2015-04/08/content_35268385_4.htm).

Please note that, when the giant panda rears up in confrontation,

  • the blackish of the chest, shoulders and forelegs contrasts sharply with the mainly whitish face and belly, and
  • any blurred pattern on the hindquarters is out of view..

Thus the whole black-and-white front of the giant panda is plausibly an extension of – to the point of substituting for – the 'pectoral flags' of other bears.

to be continued in https://www.inaturalist.org/journal/milewski/66777-does-the-colouration-of-the-giant-panda-hint-of-anti-predator-defence-by-means-of-mutilating-premolars-part-2#...

Posted by milewski milewski, June 01, 2022 20:56

Comments

Posted by milewski 4 months ago (Flag)

Chris Catton’s book ‘Pandas’ (1990, Christopher Helm, London, https://books.google.com.au/books/about/Pandas.html?id=SSQAQlRAg5gC&redir_esc=y) is nicely written.

Like most other authors, he did not consider that the giant panda might be aposematic. However, the following are relevant to the colouration of the giant panda.

On page 77, Catton describes the extreme nonchalance of adults of the giant panda in the face of attacks by the domestic dog and by humans firing bullets. (I now see that this is analogous with skunks, something that Catton overlooked.) This nonchalance and unflappability was mentioned in astonishment as long ago as 1937 by William G Sheldon in ‘Notes on the giant panda’, Journal of Mammalogy 18: 13-19.

On pages 77-78 Catton states: “It was long thought that the giant panda’s black and white coat might act as camouflage, but this theory has several flaws. First, the coat provides camouflage only in winter, when the ground is covered in snow, and for the rest of the year it makes the animal very conspicuous. The markings make the cub stand out against the blackness of its maternity den whatever the weather outside...A cub’s response to danger is to climb a tree, even when there is snow on the ground. Any snow on the branches that might have helped it blend inconspicuously into the background will be knocked off during the process, for panda cubs are not stealthy climbers. The giant panda’s black and white coat makes it conspicuous to predators when it is most vulnerable, and much of the panda’s historic range received far less snow than its present refuge...If the coat is not an effective camouflage, then what could its role possibly be? One idea has been...temperature control. A black surface both absorbs and radiates more heat than a white one. When the sun is shining animals can sunbathe and black animals will warm up more quickly; on the other hand it is more difficult for black animals to maintain their body temperature on cold, dull days...If pandas were black on top and white beneath, the theory would be more credible, but it hardly explains the detailed pattern of the giant panda’s coat...In their dense habitat the coat may help make animals conspicuous to each other and prevent them from surprising themselves by approaching too close to another of their own kind. It is usually assumed that the giant panda’s eyesight is poor, but there is actually little solid evidence for this...[more likely to be]deliberate ‘ignoring behaviour’. The pupil of the giant panda’s eye is a cat-like vertical slit...This suggests that the retina is very sensitive to light, which would account for the animal’s apparently excellent night vision. There is no good reason to assume that their day-time vision is consequently poor...Facial expressions seem to play little part in social interactions...Unlike most carnivores, giant pandas do not move their ears to signify fear or aggression, not do they erect their hair as a threat. Instead, aggression is signalled by lowering the head and staring at the opponent, a posture which as George Schaller points out duplicates the distinct eye-patches by outlining the black ears against the white neck...To signal submissiveness, a panda will put its head between its front legs, often hiding its eye-patches with its paw. This position is adopted by females during mating, and also by captive animals that are being harassed by humans – particularly vets with anaesthetic darts.“

Posted by milewski 4 months ago (Flag)

Desmond Morris (https://en.wikipedia.org/wiki/Desmond_Morris) invoked aposematism in the giant panda, as long ago as 1966.

On pages 157ff of ‘The giant panda’ by R. Morris and D. Morris, Kogan Page, London, the Morrises state

“Jaws that can crush hard bamboo stems can obviously inflict serious damage, and it is just possible that this is the panda’s ‘secret deterrent’...Its teeth are so massive and its jaws so powerful that it is just feasible that at the end of a comparatively easy pursuit, the unhappy leopard or wild dog pack is faced with the threat of a bite so terrible that it is simply not worth the risk of pressing home the advantage. This would explain three things. First, it would clear up the problem of why the giant panda has not evolved a more rapid form of escape, when sharing the region with potential killers. Second, it would explain why the animals cornered by hunters’ dogs did not even try to escape. Third, it would provide a reason for the extraordinary colour pattern of the species...dramatically conspicuous...We have only to look to the skunks for a similar state of affairs. These animals have a secret weapon...and they fear few enemies...Like the giant panda, they are rather slow and clumsy and not given to rapid fleeing...The more one thinks about it, the more the skunk-panda comparison fits...their secret weapon lies in the savage bite they can inflict with their broad jaws...when trouble finds it, it has shown remarkably little concern...its zoo personality is one of serenity rather than anxiety. By and large, then, it would seem that the famous black-and-white markings are most probably a warning pattern.”

Full credit to Desmond Morris for the idea. However, his argument, based on defence against the leopard, was incomplete for at least two reasons.

Firstly, the leopard is only half the body mass of the giant panda. To make sense, the argument should also invoke the tiger, which was formerly present in the habitat of the giant panda.

Secondly, the Morrises described the powerful bite of the giant panda in terms that were too vague, given that i) the canines of the giant panda are unimpressive, and ii) the crushing bite of the molars, however powerful, is an unconvincing candidate for a special and hidden defensive capacity.

Posted by milewski 4 months ago (Flag)

BASIC DESCRIPTION OF DENTITION IN GIANT PANDA

According to https://repository.si.edu/bitstream/handle/10088/4231/Roberts1984.pdf, the dental formula is i 3/3, c 1/1, p 4/4, m 2/3, totalling 42 teeth.

The carnassials (https://en.wikipedia.org/wiki/Carnassial) of other carnivores are replaced, in the giant panda, by premolars which I call quasi-carnassials.

The first premolar is degenerate in both jaws, and may be absent in the upper jaw.

In contrast to those of other bears, the second and third premolars are well-developed in the giant panda.

The following sketch of the canine skull (probably Canis familiaris) shows the carnassials: http://www.poodleforum.com/attachments/poodle-food/19146d1311789726-raw-feeding-question-canine-dentition.jpg.

In dogs the carnassials consist of the last upper premolar and the first lower molar.

The giant panda has converted lower molar 1 to a flat-crowned tooth, suitable for grinding bamboo. However, the last premolar on the lower jaw retains a cutting edge, and occludes with the cutting edge on the last upper premolar (derived from the upper carnassial of other bears). The quasi-carnassial premolars of the giant panda are used to cut bamboo and also presumably to mutilate attackers.

There may be some analogy with the spotted hyena (Crocuta crocuta, https://en.wikipedia.org/wiki/Spotted_hyena), which breaks bones with its premolars, not its molars.

Posted by milewski 4 months ago (Flag)

Apparently the leopard and dhole remain in small numbers in some reserves for the giant panda even today. However, the leopard at 50 kg is only about half of the body mass of a large adult giant panda, so does not satisfactorily explain the aposematism. In the case of the dhole, the explanation could make sense because this species roams through a given habitat episodically, and so a given group of the dhole may have never previously encountered a giant panda before when suddenly it is confronted with the decision of whether to attack or not.

Posted by milewski 4 months ago (Flag)

The polar bear, more than any other bear, relies on its carnassials because it is an obligate carnivore. However, it actually has carnassials so small that, if they were placed in the same toothrow as the large molars of the giant panda, might be overlooked. Indeed, I suspect that the quasi-carnassials of the giant panda are absolutely larger than the carnassials of the polar bear, despite the fact that adult females of the former species (100kg) weigh twice as much as those of the latter species (200kg). (Yes, it is true that, for females, the polar bear is only double the body mass of the giant panda).

The quasi-carnassials of the giant panda are a) small teeth relative to its grinding teeth (molars), and b) not homologous with the carnassials of other carnivores including other bears, except in the case of the last upper premolar. However, these quasi-carnassials are absolutely large and sharp enough to be the ‘hidden defensive capability’ of an aposematic animal.

The following shows the skull of the polar bear: http://www.nhc.ed.ac.uk/images/collections/mammals/carnivora/polarbearskull.jpg.

In the upper jaw, one can see four teeth, of which the first premolar is insignificant. The next premolar, i.e. the first major tooth in the upper cheek-tooth row starting from the anterior side, is PM4, the upper carnassial. This tooth and M1 occlude with lower M1, which is the lower carnassial.

What is noteworthy is that these teeth, although being crucial to a carnivore relying on an ability to butcher seals, are actually remarkably small, something acknowledged in the literature on the polar bear. What has not been acknowledged is that, in the giant panda, a) there are quasi-carnassials instead drawn from PM2+3 +4 on the upper jaw and PM2+3+4 on the lower jaw, and b) the largest of these teeth, namely P3+4, are absolutely at least as large as the carnassials of the polar bear.

Moreover, the jaws of the giant panda are far stronger than those of the polar bear. This means that the quasi-carnassials of the giant panda may actually more powerful than the carnassials of the polar bear, in slicing flesh and bone.

The following again shows how small the carnassials are in the polar bear: https://beautifullybony.files.wordpress.com/2014/03/polar-bear-and-brown-bear-skull.jpg. Yet this species, as much as any felid, relies on these shearing teeth to process all of its food.

Imagine the relative size of the skull of the giant panda, which has about half the body mass of the polar bear and a larger relative head size: its quasi-carnassials, although easily overlooked in front of the massive molars, are surely of similar in size or larger?

Posted by milewski 4 months ago (Flag)

SImilarly, it has been overlooked that the quasi-carnassials of the giant panda are about as large as the carnassials of large-bodied felids, and probably more powerful.

The reason for this oversight is as follows.

Firstly, the quasi-carnassials of the giant panda are normally used to cut bamboo, not animal flesh.

Secondly, these quasi-carnassials consist of different teeth from the true carnassials of e.g. the polar bear: PM2+3 +4 instead of upper PM4/lower M1.

And thirdly, the extreme development of M1+2 (+3 on the lower jaw) - which are used to grind bamboo - in the giant panda has been so distracting that PM2+3 have seemed insignificant by comparison.

However, given that the quasi-carnassials of the female giant panda (100kg) are actually similar in absolute size to the carnassials of females of both the polar bear (200kg) and females of the lion (100kg), they may be similarly capable of cutting through flesh even though they are used most of the time to cut through bamboo. And although the quasi-carnassials of the giant panda are not quite as sharp as carnassials, they compensate for this in what may be a stronger bite than those of either the polar bear or the lion.

The following show the dentition of the lion: https://www.alamy.com/lion-skull-side-view-image216205616.html and https://www.sciencephoto.com/media/576627/view/lion-skull-side-view and https://www.sciencephoto.com/media/429527/view/lion-skull and https://www.istockphoto.com/vector/vector-lion-skull-profile-gm154200406-14843688 and http://scienceblogs.com/retrospectacle/wp-content/blogs.dir/463/files/2012/04/i-4475457c856b35ef125cd96b7fb45025-lion-skull2.JPG.

The upper jaw has two carnassials, viz PM3+4, of which PM4 is the largest tooth in the whole dentition. The lower jaw has two carnassials, viz PM4+M1. The important thing to focus on is the combined size of these four teeth in profile.

The following shows the dentition of the giant panda: http://upload.wikimedia.org/wikipedia/commons/4/45/Giant_Panda_Skull.JPG.

Please bear in mind that the body mass of females of the giant panda is similar to that of females of the lion (about 100kg in both cases), and the head of the giant panda is if anything larger than that of the female lion. It seems that the combined size of the quasi-carnassials in the giant panda is similar to that of the carnassials in the lion.

To find the quasi-carnassials of the giant panda, which are differently derived from the carnassials of other Carnivora including other bears: start at the canines and then count in a posterior direction. Omit the first PM, which is negligibly small. Then look at PM2 and PM3, in both upper and lower jaws. These teeth are tricuspid and similar in shape and size to lower PM4 of the lion.

Posted by milewski 4 months ago (Flag)

The following news items, and comments, on the internet seem to give some support to the idea that when the giant panda bites, it tends to hang on tenaciously. When Christoper Madden was attacked, he apparently lost his whole calf muscle as a result. This seems to suggest that the giant panda chewed off this muscle as opposed to just ‘fanging’ the leg and clamping it?

http://whenpandasattack.wordpress.com/page/2/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4276236/

https://www.nbcnews.com/id/wbna15339569

http://thewayofthepanda.blogspot.com.au/2011/03/are-pandas-dangerous.html

Posted by milewski 4 months ago (Flag)

In both the domestic dog and the polar bear (https://beautifullybony.files.wordpress.com/2014/03/polar-bear-teeth.jpg.), upper PM4 and lower M1 are carnassials.

Although the carnassials of the polar bear are smaller, relative to skull size, than in the dog, they are so sharp that they can shear through the blubber of seals.

The following dentition belongs to the Asian black bear (Ursus thibetanus), which is sympatric with the giant panda but differs in dentition: https://polarbearscience.files.wordpress.com/2012/08/asiatic-black-bear-dentitionr_wikipedia-cropped.jpg.

Please note that both the upper carnassial (PM4) and the lower carnassial (M1) are poorly developed. This species of bear is not carnivorous to any extent, relying on herbaceous plants, fruit and seeds more than any other bear. The teeth to focus on, for comparison with the giant panda, are PM2 and PM3 in both upper and lower jaws, which are too poorly developed in the Asian black bear to qualify as quasi-carnassials.

In the polar bear, PM2+3 are poorly-developed in both upper and lower jaws: https://beautifullybony.files.wordpress.com/2014/03/polar-bear-and-brown-bear-skull.jpg. These teeth, although not carnassials in the polar bear, are developed into quasi-carnassials in the giant panda, a species in which the carnassial teeth of the polar bear (upper PM4 and lower M1) remain large but have been blunted.

In the giant panda it is upper PM2+3+4 and lower PM 2+3+4 that function as quasi-carnassials.

The following shows the dentition of the giant panda on the lower jaw: http://4.bp.blogspot.com/-wMkSkFuZyc4/TiAzLgpcr4I/AAAAAAAAD_Q/xlm6eHJxgGI/s400/panda%20teeth.jpg.

To count the teeth, proceed from the canines towards the posterior. PM1 is visible but too small to matter, PM2 is a quasi-carnassial, PM3 is a quasi-carnassial, and then comes the huge tooth PM4, which is a quasi-carnassial. PM2+3, although small relative to PM4 and the molars, are probably absolutely larger than PM2+3 in the polar bear.

The following shows the skull of the giant panda: http://upload.wikimedia.org/wikipedia/commons/4/45/Giant_Panda_Skull.JPG.

To find the quasi-carnassials, count back from the canines. On the upper jaw, you can see that PM2+3 each have three cusps, as do their occlusal counterparts on the lower jaw, namely PM2+3. The quasi-carnassials of the giant panda have been overlooked because a) they are different teeth from carnassials, and b) the eye is distracted by the large molars. However, the cutting power of the quasi-carnassials of the giant panda might exceed that of the carnassials of the polar bear, albeit lacking the surgical precision seen in the latter.

Posted by milewski 4 months ago (Flag)

The following news items, and comments, on the internet seem to give some support to the idea that when the giant panda bites, it tends to hang on tenaciously. When Christoper Madden was attacked, it seems like he lost his whole calf muscle as a result. This seems to suggest that the giant panda chewed off this muscle as opposed to just ‘fanging’ the leg and clamping it?

http://whenpandasattack.wordpress.com/page/2/

http://thewayofthepanda.blogspot.com.au/2011/03/are-pandas-dangerous.html

Posted by milewski 4 months ago (Flag)

The following show the dentition of the polar bear: https://beautifullybony.files.wordpress.com/2014/03/polar-bear-and-brown-bear-skull.jpg and https://beautifullybony.files.wordpress.com/2014/03/polar-bear-teeth.jpg.

The carnassials are upper PM4 and lower M1, but these are small teeth despite their formidable sharpness and their ability to shear through the blubber of seals. Please note that PM2+3, the teeth developed into extremely powerful quasi-carnassials in the giant panda, are virtually missing in the polar bear.

The following shows the lower jaw of an immature individual of the giant panda: http://4.bp.blogspot.com/-wMkSkFuZyc4/TiAzLgpcr4I/AAAAAAAAD_Q/xlm6eHJxgGI/s400/panda%20teeth.jpg.

Behind the canine, PM1 too small to see, PM2 is a quasi-carnassial, PM3 is a larger quasi-carnassial, and PM4 is the largest quasi-carnassial. Then there are two molars, the first being the longer.

The point is that PM2+3, although small relative to PM4 and the molars, are probably absolutely larger than in the polar bear, the largest-bodied strictly carnivorous land mammal on Earth.

The following shows the skull of the giant panda: http://upload.wikimedia.org/wikipedia/commons/4/45/Giant_Panda_Skull.JPG.

To find the quasi-carnassials (PM2+3+4), count back from the canines. On the upper jaw, one can see that PM2 and PM3 each have three cusps, as do their occlusal counterparts on the lower jaw, namely PM2 and PM3. The largest quasi-carnassial on both the upper and the lower jaw is PM4; in the case of the upper jaw this is homologous with the carnassial of many Carnivora. The quasi-carnassials of the giant panda have been overlooked because a) they look different from carnassials, and b) what is usually focussed on is the extreme development of the molars. But is it not evident that the shearing/cutting/clipping power of the quasi-carnassials of the giant panda might rival that of the polar bear?

Posted by milewski 4 months ago (Flag)

The following show the mandibular dentition of the giant panda from above: https://www.nature.com/articles/s41598-021-93808-2/figures/1.

The quasi-carnassials are P2, P3, and P4.

In the Asian black bear (https://en.wikipedia.org/wiki/Asian_black_bear#/media/File:037tiger.jpg), these teeth are relatively small, except for upper pm4. The relatively small fourth lower premolar (PM4) of the Asian black bear has been enlarged in the giant panda, to form a tight-fitting set with lower PM2+3.

The following (https://40.media.tumblr.com/5566657b2392097e7949c441b3dd26d7/tumblr_n13wsig4SL1snzwjto2_500.jpg) shows the upper jaw of the Asian black bear, labelled as Selenarctos. The topmost dentition is that of Ursus (brown bear), showing the lack of carnassials in this genus.

Compare the skull of Ursus with that of a like-size felid. The bear skull typically lacks carnassials whereas the felid skull has the ultimate carnassials among Carnivora. In felids, the main carnassials are upper PM4 and lower M1. Basically the whole cheek-tooth row is converted to carnassials in felids (http://o.quizlet.com/uwfx-jIPa5U8nZcgM0UFIA_m.jpg). To envisage the quasi-carnassials of the giant panda, fill in the diastema of Ursus with teeth of similar size to the carnassials of the felid.

Is it, then, possible that PM3 of the giant panda, in either the upper or the lower jaw, is absolutely larger than the carnassial, PM4 in upper or M1 in lower, of the lion? It seems likely that the main quasi-carnassials of the giant panda are larger than the subsidiary carnassials, viz PM2 (upper) and PM4 (lower), of the lion. Given that the lion can butcher a buffalo with these carnassials, is it not possible that the giant panda can powerfully injure an attacker despite its canine teeth being far inferior to those of the lion?

In the giant panda, the main function of the canine teeth may be clamping so that the quasi-carnassials can perform their cutting of the flesh of an attacker.

Posted by milewski 4 months ago (Flag)

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