Why is the giant panda black-and-white? (concise version)

@maxallen @aguilita @marcelo_aranda @biohexx1 @jwidness @zarek @seasav @douglasriverside @napoleon1799 @oviscanadensis_connerties @walkwithbears @bears-101 @thebirdnerd @gwark @mc1991 @ursusont @chewitt1 @pelagicgraf @jayras @rangertreaty50 @williamwisephoto @bobby23 @frostfox @kmccartney3521 @suepemberton

(For details see https://www.inaturalist.org/journal/milewski/66693-does-the-colouration-of-the-giant-panda-hint-of-anti-predator-defence-by-means-of-mutilating-premolars-part-1#)

The black-and-white pattern of the giant panda (Ailuropoda melanoleuca) - which is remarkably uniform regardless of age or sex - was first interpreted by Desmond Morris as warning colouration half a century ago. However, nobody seems to have taken that suggestion seriously.

This bamboo-chewing bear has an exceptionally strong bite. However, all carnivores defend themselves by biting, and teeth can be displayed directly by facial expression.

So, was it far-fetched to suggest that the giant panda has evolved a conspicuous, skunk-like pattern on its coat just to warn potential predators of teeth that have not particularly evolved for self-defence? (The most relevant predators, formerly occurring - albeit in spare populations - throughout the habitat of the giant panda, were the tiger (Panthera tigris) and the dhole (Cuon alpinus), the latter being far smaller-bodied than the giant panda but attacking gregariously.)

As it turns out, the giant panda does possess a hidden defensive capability, previously overlooked even by Desmond Morris. This species is unique among Carnivora in possessing 'mutilar', quasi-carnassial teeth. These are clipping/mangling premolars, which function both to cut and peel bamboo and to mutilate attackers.

The quasi-carnassials of the giant panda, namely premolars 2-4 on both the upper and the lower jaw, combine three features unusual among Carnivora:

  • tight occlusion between upper and lower counterparts, in contrast to the non-/partial occlusion of the premolars in most other Carnivora including other bears (Ursidae), which tend to have a diastema (https://en.wikipedia.org/wiki/Diastema),
  • placement just behind the canines, close enough to the front of the mouth to allow direct biting, and
  • cusps sharp and sturdy enough to cut/break flesh and bone, driven by massive jaw muscles on a robust skull adapted to chew woody food (bamboo).

In most other Carnivora, the only premolar used for shearing/slicing is the fourth upper premolar; this upper carnassial tooth is used for processing food, not fighting in self-defence. What distinguishes the giant panda is that this and five other premolars on each side (left or right) have been converted into a set of quasi-carnassials. These are not as sharp as the carnassials of the polar bear, felids, and canids, but are as large and driven by equally strong musculature, while also being less fragile.

This may be in a sense absolutely as well as relatively the largest/strongest set of premolars of any member of the Carnivora. However, its significance has been overshadowed by the exceptional molars of the giant panda – which are unsuited to self-defence.

Crucial to explaining the colouration of the giant panda is that the hazard of the quasi-carnassials is not self-evident. As a result this species has been overlooked as an animal uniquely capable of mutilating an attacker’s body with a clipping/mangling mechanism evolved for self-defence as much as for eating.

Instead of fang-baring or showing its (modest) claws in confrontation, the giant panda instead maintains a menacingly expressionless face - partly compensated for, in its social life, by a complex repertoire of vocalisations.

In its strictest definition, aposematism (https://en.wikipedia.org/wiki/Aposematism) is not just warning colouration, but a flagging - at the scale of the whole body - of a hidden defensive capability. Inasmuch as it conforms, the giant panda may be the largest-bodied aposematic organism on Earth.

Posted by milewski milewski, June 04, 2022 02:33

Comments

The following, even more concise, may fail to cover interesting details:

The giant panda has extreme colouration, which seems to advertise it. This seems to have lacked a satisfactory explanation.

What is the adaptive advantage of whole-body conspicuousness – bearing in mind that the giant panda is the most herbivorous of Carnivora?

The only other members of the Carnivora that are specialised for conspicuousness all possess ‘hidden weapons’. The conspicuousness is warning colouration directed at other predatory animals.

At first sight, the giant panda seems relatively defenceless. Its canines are short, and its claws are unimpressive compared with those of other bears. It can climb trees, but not well enough to escape the leopard.

If the giant panda possesses a secret weapon, what could that be?

The giant panda has an exceptionally powerful bite owing to its woody diet. It depends on bamboo, requiring extremely powerful chewing by extremely compact jaws and teeth.

However, this in itself does not explain aposematic colouration, because other carnivores advertise their bite directly by facial expression.

The answer is: the hidden weapon of the giant panda is 'mutilar' teeth: premolars previously unrecognised for their capacity to mutilate attackers and previously not distinguished from the bamboo-grinding molars.

In reality, the tight-fitting premolars of the giant panda are unusual among bears and other Carnivora, and their biting power is only partly explained by a diet of bamboo.

All other Carnivora rely on their canines for self-defence by means of biting. The premolars are either too far back in the mouth (cats), unable to occlude fully between upper and lower jaw (dogs), too puny to matter in biting (sea lions and all bears other than giant panda), or massive and conical and advertised directly by fang-baring (hyenas). The giant panda is unique in having premolars capable of inflicting a mutilating bite, but not looking impressive.

Posted by milewski 4 months ago (Flag)

Because the threat of these premolars remains hidden, fang-baring facial expressions would be pointless. This is in contrast to e.g. the spotted hyena (Crocuta crocuta), which opens the mouth, lips and gape so wide that it displays long canines as well as conical premolars which function mainly in foraging but can also be deployed in a bone-crushing bite in self-defence. The short canines of the giant panda are unimpressive, but compatible with the quasi-carnassials. They do not obstruct the deployment of the premolars in a defensive bite, instead aiding it by a holding (as opposed to puncturing) action.

Posted by milewski 4 months ago (Flag)

It seems ironic that the short muzzle and broad face that make the giant panda charismatic to human eyes should actually be intimidating.

It also seems ironic that, by virtue of the strength of its jaws, the giant panda could be the most dangerous bear for its body size, despite being perhaps the least carnivorous of all Carnivora.

Posted by milewski 4 months ago (Flag)

The giant panda and the sabre-tooth felid Smilodon may be opposites in the following way. In the former, the distinctive front teeth (quasi-carnassial premolars) are used for defence but not for offence. In the latter, the distinctive front teeth (long canines) were presumably used for offense (in killing prey) but not defence (see https://www.inaturalist.org/journal/milewski/66573-did-authentic-mega-killers-keep-their-mouths-shut#).

Posted by milewski 4 months ago (Flag)

An aspect of the rationale for aposematism in the giant panda is that the form of its premolars may not be fully explained by its herbivory per se. All bears other than the giant panda lack well-developed premolars (other than upper PM4). This includes the extinct cave bear (Ursus speleaus, https://en.wikipedia.org/wiki/Cave_bear), which had large flat molars and probably depended mainly on plant food milled by means of these molars. The giant panda is even more extreme on the cline illustrated from the polar bear to the cave bear, but it is also aberrant in having well-developed, non-grinding premolars set in a tight row with a minimum diastema. It is true that a major adaptive value of the premolars is to cut and peel bamboo (setting the giant panda apart from the cave bear), but an equally important adaptive value might be defence against predators.

Posted by milewski 4 months ago (Flag)

Is the giant panda is unique in its dentition, w.r.t. the full occlusion of its premolars? Here I check otters, bearing in mind that the sea otter (Enhydra lutris, https://www.inaturalist.org/taxa/41860-Enhydra-lutris) is the largest-bodied of all mustelids, and the only one approaching the body mass of the giant panda.

The skull of the sea otter is aberrant, with three premolars that are even more ‘crowded’ than those of the giant panda. However, there is limited analogy because there are no carnassials or other sharp cheek-teeth in the sea otter.
 
The following shows Lutra. There is no diastema and there are three premolars, with apparently carnassial blades.
 
http://chestofbooks.com/animals/Manual-Of-Zoology/images/Fig-432-Under-view-of-the-skull-of-the-common-Otter-Af.jpg
 
However, the following profile view shows that, as in most other Carnivora, the premolars do not fully occlude in Lutra. Typical otters remain different from the giant panda in this way.
 
http://upload.wikimedia.org/wikipedia/commons/c/cd/Lutra_lutra_02_MWNH_414.jpg
 
The strong premolars of the sea otter are used, as in the giant panda, to process hard foods. However, they are blunt, not quasi-carnassial, and with age they become molariform.
 
https://farm2.staticflickr.com/1384/1288437581_dde2d6a1f1.jpg
 
The following show that the sea otter is like the giant panda in that its ‘crowded’ premolars do fully occlude. However, these cannot be described as quasi-carnassials, so they have no particular potential as defensive teeth. Besides, most of the predators of the sea otter would swallow the animal whole, making self-defence by means of the teeth redundant.
 
http://dpquiz.co.uk/joomla25/images/fqq/skull_sea-otter.jpg

http://4.bp.blogspot.com/-Ec8BAK51gsY/UZ8o_rXgchI/AAAAAAAAKrg/RTdNTzcqLr0/s1600/sea_otter_skull_replica_ss312_m784.jpg
 
The following two specimens of the sea otter seem relatively young, with largely unworn teeth, but the cusps on the premolars are too blunt to function as quasi-carnassials.
 
https://farm4.staticflickr.com/3191/2558236308_b5f6725c72.jpg

http://m0.i.pbase.com/o6/14/755514/1/84308660.iXNd9UXe.SkullOZ9W4132.jpg
 
The sea otter also has a limited defensive bite in the case of its canines. The upper canines seem rather intimidating. However, the lower canines are short and blunt; they are used to open shells, and often break as the animal ages.

The following shows that the lower canine does not fully fit into the gap between upper incisor 3 and the upper canine. The main defensive bite of the sea otter is presumably by means of its upper canines, but this species seems to differ from most Carnivora in lacking any particularly well-developed weapon. Despite its short face and powerful jaws, it cannot rival the giant panda in a defensive quasi-carnassial bite.
 
http://www.skullsunlimited.com/userfiles/image/variants_large_4627.jpg

Posted by milewski 4 months ago (Flag)

The following shows how deceptive the carnassials can be in bears.

In the following skull of the polar bear (Ursus maritimus), the upper carnassial (PM4) is the third from the back, just behind the mere peg that is upper PM3. The lower carnassial (lower M1) is the second tooth in the mandibular cheek-tooth row behind the diastema. Please note that the carnassials, whether on upper or lower jaw, are smaller than upper incisor 3, a tooth to which nobody ascribes any particular importance although obviously it acts to support the action of the lower canine in gripping prey.
 
https://beautifullybony.files.wordpress.com/2014/03/p-bear.jpg
 
The following again show the occlusion of the carnassials in the polar bear. The upper carnassial (PM4, just posterior to the peg that is upper PM3) occludes with its tallest cusp between lower PM4 (a supporter of the carnassial action) and the anterior cusp of lower M1. Although the carnassials clearly occlude completely, they are not impressive-looking teeth.
 
https://www.alamy.com/polar-bear-skull-image217042696.html
https://es.123rf.com/photo_8069030_polar-bear-skull-profile-showing-the-large-predator-canines-isolated-on-white-background.html
https://www.acornnaturalists.com/bear-polar-skull-replica.html
 
The final photo once again shows that the all-important carnassials are smaller than the functionally forgettable upper incisor 3. The polar bear has impressive canines (http://icestories.exploratorium.edu/dispatches/wp-content/uploads/2010/04/21-april-3.jpg and https://twitter.com/aederocher/status/1123669884292956162),but it certainly does not have impressive-looking carnassials. Again, this photo suggests that lower PM4, which looks rather carnassial in isolation, does not occlude completely enough with upper PM4 to qualify as fully carnassial.

http://www.nature-watch.com/images/products/large/806t.jpg

My point:
The insignificant-looking carnassial set, viz upper PM4 and lower M1 (plus lower PM4) in this photo are the crucial teeth in what is functionally the most carnassial of all bear species. Of what, then, are the quasi-carnassial premolars of the giant panda capable?

Posted by milewski 4 months ago (Flag)

Further to the point that the carnassials of the polar bear are no more impressive-looking than the premolars of the giant panda:

The following shows the dentition of the polar bear (Ursus maritimus):
 
http://upload.wikimedia.org/wikipedia/commons/c/ce/MSU_V2P1a_-_Ursus_maritimus_skull.png
 
The upper cheek-teeth consist of: PM3 (small), PM4 (far smaller than the molars but THE carnassial of the polar bear, and THE tooth it uses to process all its prey), then two molars (which as in all bears are the largest cheek-teeth and are blunt). The life of the polar bear depends on that small tooth, second in the visible toothrow, which does not even seem sharp from this angle. Would anyone even suspect that it can butcher seals and that it provides the polar bear’s only means to do so?
Lower jaw: THE carnassial on the mandible is the anterior cusp on the second tooth (lower M1) in the cheektooth-row of four teeth. Lower PM 4 also looks carnassial in form although smaller than lower M1.
 
The following shows the occlusion of the cheek-teeth of the polar bear: http://static5.depositphotos.com/1005858/408/i/950/depositphotos_4089182-Polar-bear-skull-on-black.jpg.

Proceeding from anterior to posterior in the upper jaw, that tooth just behind the upper canine is a peg-like, irrelevant PM1. Then a diastema, the an equally peg-like upper PM3. Then THE upper carnassial, PM4, which is not a large tooth in the scheme of things. Then the two molars, useless for shearing/slicing. On the lower jaw: after the diastema we have PM4, occluding weakly with the peg that is upper PM3. Then M1 (THE lower carnassial), then two more molars. The upper carnassial (PM4) occludes with the anterior cusp of the lower carnassial (M1). Note the small shearing edge on which the ability of the polar bear to process every mean depends.
    
The following is another view of the cheek-teeth of the polar bear (on the left): https://beautifullybony.files.wordpress.com/2014/03/polar-bear-and-brown-bear-skull.jpg.

The upper carnassial is third from the back and the lower carnassial is second from the front after the diastema. The polar bear’s carnassials are no more impressive looking than those of the brown bear, which eats mainly plants and does not depend on slicing flesh. This is a considerable functional difference hinging on a subtle morphological difference.

Posted by milewski 4 months ago (Flag)

The wolverine (Gulo gulo) and the giant panda both have a reputation for mangling metal (in the case of the giant panda, the reputation is for licking metal and chewing up cookware).

The wolverine may be the most bear-like of the mustelids, but its teeth are not particularly bear-like. The molars are too poorly developed, the premolars (including upper PM4) are too well-developed, and the incisors are better-developed than those of bears. But most of the premolars of the wolverine are – as in bears other than the giant panda – apparently incapable of a defensive bite of the shearing/slicing kind.
 
The following show the dentition of the wolverine:

http://wolverinefoundation.org/wp-content/uploads/2010/12/dental.gif

http://wolverinefoundation.org/dentition-of-the-wolverine

The main differences from the giant panda are a) fewer and smaller molars, b) massive carnassials, and c) particularly well-developed incisors. Upper M1 is set at right angles to the rest of the toothrow.
 
The following show that the premolar rows of the wolverine somewhat resemble this of the giant panda:

http://fc03.deviantart.net/fs4/i/2004/260/a/0/Wolverine_Skull_1_by_rgstock777.jpg

http://www.mnh.si.edu/mna/images/skulls/815432214160020.jpg

http://fc00.deviantart.net/fs6/i/2005/048/2/3/Wolverine_skull_3_by_rgstock777.jpg

In the wolverine, the premolar rows lack the gaps seen in e.g. canids. The largest teeth in the cheek-tooth-rows are the usual ones for Carnivora, namely the carnassials upper PM4 and lower M1. Upper PM2+3 and lower PM2+3+4 have a carnassial shape (i.e. a blade), and fit continuously all the way from P1 to the carnassials.

The wolverine is regarded as ‘the hyena of the North’. However, its dentition differs from that of hyenas because PM3 is not a large peg in the wolverine.
 
The following of the wolverine skull show that, despite the compactness of the premolar rows, PM2-3 (upper) and PM2-4 (lower) do not occlude tightly.

http://www.promiselandranch.net/Images%20and%20Buttons/Skulls16.jpg

http://www.skullsunlimited.com/userfiles/image/variants_large_4328.jpg

https://www.boneroom.com/img/idPics/2964_1large.jpg

The premolars of the wolverine are unsuited to defensive biting. Their main function seems to be to grip food so that the carnassials can be brought to bear. Rather than the premolars being especially powerful, it is the incisors of the wolverine that are proportionately more robust than in the giant panda. The lower incisor row of the wolverine is crowded to the point of being staggered, suggesting that they can inflict a serious defensive bite, a mutilation rather than a nip. The wolverine fang-bears readily, displaying the canines and also the incisors.

Posted by milewski 4 months ago (Flag)

Most of the premolars of canids do not qualify as carnassials. They function for gripping, not shearing/slicing. No canid can bite an enemy hard with its premolars.
 
The wolf (Canis lupus) has the same dental formula as the giant panda, viz. I 3/3, C 1/1, PM 4/4, M 2/3. However, the premolars other than upper PM4 (the upper carnassial, which occludes with lower M1), cannot fully close. By contrast, the giant panda can completely close the entire premolar row from PM2 to PM4 in the upper jaw and from PM2 through PM3 to PM4 in the lower jaw – exerting a bite that may be unique among Carnivora, and possibly crucial for self-defence.
 
The premolars of the giant panda unusually combine a) quasi-carnassial shape, b) complete occlusion, and c) location close enough to the jaw muscles to exert extreme force. An this be fully explained by the processing of bamboo?
 
The following show that, in the wolf, the premolars (other than upper PM4, the main carnassial) remain apart even when the jaw is fully closed. There remains a gap between upper PM1-3 and lower PM1-4. The wolf relies on its canines to injure an adversary, and neither its premolars nor its carnassials are used in defensive biting.
 
https://www.darwinandwallace.com/products/wolf-skull-siberian-gray-wolf-cast-replica-canis-lupus-bc-004

http://www.boneclones.com/images/bc-020t-lg.jpg

http://digimorph.org/specimens/Canis_lupus_lycaon/specimen.jpg

http://www.nhc.ed.ac.uk/images/collections/mammals/carnivora/wolfskull.jpg

https://www.acornnaturalists.com/wolf-american-gray-skull-replica.html
 
The following, of the skull of the wolf, shows the jaws fully closed:

http://sibar.files.wordpress.com/2008/10/sm-495-lg1.jpg

Note the complete fit of the lower canine into the slot between upper incisor and canine. PM1-3 in the upper jaw do touch PM2-4 in the lower jaw. However, this occlusion is not deep enough to allow these PM to function as carnassials, nor to bite down hard enough that the full force of the jaws can be brought to bear on the premolar rows. PM4 (the main carnassial) is too far back in the mouth to be used in a self-defensive bite).
 
The following show the corresponding dentition of the giant panda:

http://www.educationalbiofacts.com/images/RS330%20-%20Giant%20Panda%20skull.JPG

The premolars function as quasi-carnassials in their complete occlusion and thus deep shearing/slicing action. Although the premolars of the giant panda are smaller than its molars, they are exceptionally well-developed among Carnivora. This makes the premolars more distinctive of the giant panda than the molars, which are rivalled by e.g. Ursus spelaeus.

Whereas in the wolf most of the premolars are merely gripping teeth, in the giant panda it is instead the canines that seem to be merely gripping teeth. These canines are too short to obstruct the application of the quasi-carnassial premolar row in self-defence.

Posted by milewski 4 months ago (Flag)

ETYMOLOGICAL NOTE

What should we call the quasi-carnassial premolars of the giant panda, which are tight-set, fully occluding, and not fully explained by the cutting and peeling of bamboo?

Incisor comes from the Latin verb incidere, to cut into, and its derived form incisivus. Molar comes from the Latin noun mola, millstone. The Latin for the verb ‘to mutilate’ is mutilare, from which I reason that the new word ‘mutilar’ can be derived. A mutilar is a tooth that mutilates, in the same sense that a molar is a tooth that grinds and an incisor is a tooth that cuts into things.

Carnassial comes from the Latin carn- (noun for flesh) and its French derivation, the adjective carnassier, meaning carnivorous.

So, my suggestion is that the giant panda possesses mutilar teeth, and may be the only mammal (animal?) to do so. A mutilar tooth is defined as a premolar (other than upper PM4), positioned to occlude a similar tooth on the opposite jaw, that functions as a clipper/cutter/mangler, not a grinder. Where the giant panda has mutilars, other Carnivora tend to have a combination of diastema and premolars with only partial occlusion, which are incapable of clipping objects.

The hook-lipped rhino (Diceros bicornis) has clipping premolars (used to clip woody stems up to a diameter of ca 1 cm), but these are not mutilars because they a) also occlude fully as grinding teeth, and b) are not used in self-defence.

Posted by milewski 4 months ago (Flag)

Add a Comment

Sign In or Sign Up to add comments