The Papio Problem
Eric Falck
Anthropology 409
10 March 2010
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Introduction
Originally, taxonomists considered the genus Mandrillus and the genus Papio to be
sister taxa. Within the larger organization of the systematic classification of primates, this
seems highly plausible utilizing the morphological studies previously recorded. Within the
papionini clade, including the genera Macaca, Cercocebus, Lophocebus, Mandrillus, Papio, and
Therapithecus, there appeared to be no more parsimonious list than to have Mandrillus and
Papio united (Hill VIII, 1970). However, molecular research beginning in the1970’s began
piecing together a different phylogeny, which separates mangabeys into two genera,
Cercocebus and Lophocebus, with Mandrillus and Papio splitting off of one of the separate
groups, respectively (Diostell, 1994). Several researchers began to question the lack of
morphological synapomorphies among Cercocebus and Mandrillus as well as Lophocebus and
Papio (Fleagle and McGraw, 2002). In light of all the new findings, I am presenting a
generalized understanding of the progression into the new classification system.
Mangabeys
The Mangabeys have been acknowledged as an intermediate form between guenons
and macaques (Hill VII, 1970). They are large, gracile monkeys that have long tails and dark fur,
contrasting guenons that fit into the tribe Papionini as Groves (1978) characterizes (pg 4):
1. Diploid chromosome number 42.
2. Lingual surface of lower incisors lacks enamel (DELSON, 1973).
3. Sexual skin changes (seasonal or otherwise) in females.
4. A tendency to elongation of the facial skeleton.
5. Molar flare (DELSON, 1973), especially in larger toothed forms.
6. Ma develops a hypoconulid in all but the smallest toothed
forms.
7. Lower canines of females somewhat incisiform--not slender
and masculinised as in Cercopithecini.
8. Highly developed facial mimicry.
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However, Groves (1978) discusses the similarities found between mangabeys and guenons
morphologies. However, his research focuses on separating the formerly monophyletic group
morphologically after becoming aware of molecular data. Some of these similarities include
Cercocebus having a flexed braincase, infero-medial angle of the orbit that is cut away, or a
lachrymal fossa that is rounded. Lophocebus also carries Cercopithecus traits such as a large
molar foramen (Groves, 1978).
It is important to note that Hill (VII,1970) does not differentiate between the two genera
of mangabeys, Cercocebus and Lophocebus, which allowed for comparisons to both
Papio,shape of the ischial callosities, as well as Mandrillus, catamenial swelling, because of the
lack of clarification to which, Cercocebus or Lophocebus, he was referring to (Hill VIII, 1970).
Groves (1978), on the other hand, negates incorporating genus Mandrillus, which allows for the
organization of Papio and Mandrillus as sister taxa to be unchallenged.
Papio and Mandrillus
Superficial morphological characteristics do allow create for an acceptable sister
relationship between the taxa of Papio and Mandrillus. Notably in John Fleagle’s college text
book Primate Adaptation and Evolution, baboons are credited as the largest nonhominid
primates over mandrills; probably due to the original grouping of the two taxa into the same
genus. However, contradicting his own statement, he marks mandrills reaching a body mass of
31 kg and baboons toping at approximately 29.8 kg (Fleagle, 1998). The fact that their average
body sizes are recorded at only a 1.2 kg difference is one of the factors that lead to their
sisterhood.
Before actual classification of the genus was recorded, Hill (VIII, 1970) referenced
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Gesner (1551) discussing a Papio, but it was accompanied, in the German edition of his work, by
a picture of a mandrill. Both have large rostrums as well as being described as more canine like
(Hill VIII, 1970). Both Fleagle (1998) and Hill (VIII, 1970) discuss the importance of sexual
dimorphism, especially within the body size and size of teeth for both. Selection under the
same pressure can result in convergence on similar character states. Mandrills, however,
posses an extreme form of sexual dimorphism, the male mandrills have brightly colored
rostrums that are even more pronounced/developed the higher the rank of the male (Setchell,
2005). Common discussion of the development of this coloration as discussed in Anthropology
409 reflects the necessity to visually discern potential mates in the dark forest as mandrills are
discussed as being baboons moving into the forest. However, it would be interesting to
research if this was a sensory exploitation of a preexisting aesthetic preference in females. This
could have assisted in supporting the phylogenetic system; testing if female Papio individuals
are predisposed to favor a colored male for more behavioral similarities along with being
ground dwelling, omnivorous, and similar in sociality (White and Wickings, 2002).
The results may not favor the closeness of the Papio-Mandrillus relationship, and the
study should be applied to all members of the papionini tribe to elicit the preexisting aesthetic
among all, neither, or a select group. As molecular studies began to show, Mangabeys are a
diphyletic group that each gave rise to one of the dog-like genera.
Molecular Evidence
Beginning in the 1970s scientists began testing the limits of phylogenies based on
morphological evidence for the papionini tribe. Disotell (1994) created an extensive reanalysis
and investigation into most, if not all, the molecular research. It is observable that most
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molecular data only concluded that Mandrillus can be removed from a close relationship to
Papio because studies on proteins such as hemoglobin α- and β-chains and adenylate kinase
place Papio and Theropithecus in a grouping, and immunological distances between papionin
albumins place mangabeys, macaques, and mandrills equal distance from closely related gelata
baboons and Papio baboons (Barnicot and Wade, 1970; Sarich 1970) Notably as well, this
eliminated Szalay and Delson (1970) hypothesis that Theropithecus was basal to mangabeys,
baboons and mandrills. Though Harris (2000) suggests that the actual linage of Lophocebus,
Papio, and Theropithecus cannot be determined because of the rapid and recent diversity
within this grouping.
It appears as though, not until Cronin and Sarich (1976) began testing molecular
similarities within the Tribe based on new phylogenies being created for New World monkeys
through molecular testing, that there was an investigation for a split in the mangabey grouping.
The resulting data showed paraphyly in the Mangabey classification with resulting evidence
supporting a similarity to what would be known as Cercocebus to Mandrillus and Lophocebus to
Papio. This idea was further perpetuated by chromosomal banding patterns on chromosomes
10 and 12 and the COII gene, which is shows immense degrees of mutations/deviations
(Disotell, 1994).
The problem still persisted that morphological characteristics did not support this new
phylogeny. Mandrills are more closely related to the terrestrial mangabeys, but have
converged on the same physical states of the baboons. Convergent evolution suggests that the
same pressures on two species will create similar morphologies, but there should be some
characteristics that stay similar.
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Morphological Similarties Supporting New Phylogeny
Lophocebus and Papio were first supported morphologically similar (Fleagle and
McGraw 1999). Groves (1978) found the separation between Cercocebus and Lophocebus, he
actually positioned Lophocebus closer to Papio and Thereopithecus either directly or indirectly
by stating that the characteristics were more Old World Monkey like. Directly, he found
Lophocebus mandiblar margins, upper and lower, are anteriorly diverged because the upper
margin has become elevated. Also, the both have slit-like lachrymal fossa. In the
Lophocebus/Papio/Theropithecus grouping, Groves noted that they always have multiple
foramina with similar placement.
More recently and specifically, Fleagle and McGraw (1999; Fleagle and McGraw, 2002)
showed the similarities between Cercocebus and Mandrillus, an analysis left out of Groves
(1978), and this expanded upon the morphological similarities between Lophocebus, Papio, and
Theropithecus.
Dentally, the synapomorphies existing between Cercocebus and Mandrillus are
hypothesized to be advantages for their similar eating habits of hard fruit seeds and nuts on the
forest floor. Both genera have large and well rounded premolars for crushing the hard
substances they sustain themselves on (Fleagle and McGraw, 1999). Figure 18 and 19 of Fleagle
and McGraw (2002) plotted the relative premolar size, upper and lower respectively, and the
results so Cercocebus/Mandrillus averages for both to be in the range of 70-85 units with
Lophocebus/Papio to be in the 55-65 units range. While Fleagle and McGraw (1999) said that
Lophocebus individuals do consume hard nuts, Daegling and McGraw (2007) reported that this
group does not crush the nuts with their premolars. This research went further cranially, and
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discovered that other than the similarities in teeth, the mandibular size and shape correlation
for Lophocebus-Papio and Cercocebus-Mandrillus is low; allometry seems to be low as Papio
and Mandrillus are not reflecting the same relative changes. This is probable because of the
general diet of baboons and the stress of the mandrills diet.
The diet/behavioral patterns that unify Cercocebus and Mandrillus are also reflecting in
the post-cranial similarities. The scapula of these two genera have an extensive superiorinferior surface which enhances the attachment of muscles; attachment of the teres major that
this depth enhances is supportive for vertical climbing, which the terrestrial mangabeys and
mandrills have been documented doing. Continuing on enhancements for muscle attachment
in the upper appendicular skeleton, Cercocebus and Mandrillus have well developed lateral
projections on their humerii with small olecronon. The lower appendicular morphologies are
less distinguishable than the upper though a larger illium, projecting lip on the medial side of
the femur, and a rounder tibial shaft are found in the Cercocebus-Mandrillus grouping and also
enhance vertical climbing. On a side not, these are also primitive features found in macaques
(Fleagle and McGraw 2002).
Conclusion and Future Research
As research expanded and became more specific, on the molecular level and
morphological level, there was a change in the systematic classification of a tribe that appeared
to fit so well together in the first place. This is very exciting, but also creates a sense of distrust
for previous research. Distrust may not be a bad thing, it reminds the scientific community that
the information in the field is falsifiable and allows for reinvestigations and analyses. For future
focuses apart from the possible sensory exploitation of mandrills discussed earlier, it would be
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promising to look from different viewpoints at data that was unexplainable. In the case of the
low allometry correlation for the mandibular size from Cercocebus to Mandrillus and
Lophocebus to Papio fround in Daegling and McGraw (2007), Groves (1978) pointed out that
“The only skull feature common to all mangabeys, the suborbital fossa, is, as has been seen (no.
4) differently formed in the two, and so has probably developed independently in response,
perhaps, to facial shortening from a long-faced ancestor to preserve a complex facial
musculature” (pg 7). Discerning characteristics that could show similar allometry might be
found in characters that are still functionally similar between the baboons, mandrills, and
mangabeys. Reconstructing how things have developed, by specialization or laws of allometry,
can discern the roots of the human lineage and how things evolved.
Acknowledgements
I’d like to thank Kevin Lumney, Comparative Vertebrate Anatomy professor, and
Michael Kelly Bruce, Kinesiology of Dance Professor, for teaching me all the names of bones,
muscles and their attributes.
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