Are the canine teeth of baboon-like macaques different from those of baboons?

(writing in progress)

Baboons (Papio, Mandrillus, Theropithecus) occur in Africa and Arabia. Their closest counterparts in Eurasia - albeit less specialised - are the larger-bodied spp. of macaques (Macaca).

All spp. of Old World monkeys feature well-developed canine teeth in adult males.

Therefore, one might expect that the canine teeth of baboons and macaques are similar

I have an impression that the canine teeth of certain spp. of macaques are different, anatomically, from those of baboons.
 
I first noticed this when going through a textbook edited by Caroline Pond (1990) called ‘Diversity of Organisms’ (part of the series ‘Biology: Form and Function’, by Hodder & Stoughton, for The Open University). On page 72 is a photograph of the skull of the adult male of one of the two species of pig-tailed macaques. This shows the dentition clearly in full profile. To my surprise, the upper canine is so broad along its anterior-posterior axis, at its base at the gum-line, that it looks different from those of baboons.

Photos of the skulls of male macaques are scarce. This may explain why this difference - if real - has been overlooked previously.
 
Unfortunately I cannot show this photograph, and there is nothing similar on the Web. So, I have compiled as many relevant photos, below, as I can.
 
In both baboons and macaques, the canine teeth of males are designed for a combination of stabbing and slicing. However, I now realise that in macaques the emphasis is more on slicing, while in baboons the emphasis is more on stabbing. This may make sense, given that the muzzle is considerably shorter in macaques – including even the pig-tailed macaques, which are perhaps the most baboon-like of Eurasian monkeys – than in baboons.
 
As far as I know, neither baboons nor macaques use the canine teeth when processing food. These teeth are well-developed only in adult males, and their significance is largely in competition among males. They also have a corollary function in anti-predator defence.

In gibbons (which are apes, not monkeys), the canines are long and sharp in both sexes. Because gibbons are essentially monogamous and non-social, I assume that the function of the canines in gibbons is mainly anti-predatory.
 
The following shows a mature male of a species of pig-tailed macaque. Among all the macaques, it is the pig-tailed macaques which approach baboons most closely in body form and body size.
 http://3.bp.blogspot.com/-USRSCBiusJQ/VogO9opmWlI/AAAAAAAAMyM/OTNLghGJNWY/s1600/Pig-tailed%2Bmacaque%252C%2Bpublic%2Bdomain.jpg

  
The following shows the skull of a male individual of another species of macaque.

Note that the upper canine, although well-developed and dangerous-looking, is not as proportionately long and slender as in baboons. This is partly because its breadth along the anterior-posterior axis (at the gumline) is relatively great.

This indicates a kind of ‘blade’ effect because it is unlikely that the cross-section of this tooth at its base is circular. The photo I have before me in Pond (1990) shows an even broader canine than this.

Macaca thibetana male:
http://rafael.glendale.edu/skull/pd-macaque_m/left.htm

 
The following shows another species of macaque with a relatively broad, rather than long and thin, upper canine as a mark of masculinity. I do not know how typical this is for this species. However, I have not seen this blade-like form of the upper canine in any baboon.

Macaca mulatta male:
http://rafael.glendale.edu/skull/macaca_mulatta/left.htm

 
The following is a reminder of the form of the upper canine in male baboons. Note that the upper canine is long without a noticeably broad base. Even in baboons, the upper canine is honed to form a blade, by wear against the specialised lower premolars - which are shown in this photo. However, the blade on these canines is not obvious from this perspective. 

http://c8.alamy.com/comp/DXNG9H/skull-of-baboon-papio-in-front-of-black-background-side-view-DXNG9H.jpg

 
Finally, the following again shows how long and slender the upper canines can be in fully mature males of the chacma baboon. This is noticeably different from the form of the tooth in the photo I have before me (Pond 1990) of a species of pig-tailed macaque. Both the length of the muzzle and the length and slenderness of the upper canine seem to differ between baboons and the most baboon-like of macaques. 

Papio ursinus male:
http://www.skullsite.co.uk/Chacma/papio_urs_M_lat_800.jpg

(writing in progress)

הועלה ב-יולי 5, 2022 10:06 אחה"צ על ידי milewski