Allen's swamp monkey (Allenopithecus nigroviridis) is a species of Old World monkey endemic to swamps and riparian forests in the central Congo Basin.
Although it was once considered to be a guenon, is has been recognized as the only member of the genus Allenopithecus since the 1920s, and is now regarded as a sister clade of the guenons. Despite being a cercopithecin, it exhibits a pastiche of traits typical of papionins, characterizing Allen's swamp monkey as a primitive member of the subfamily Cercopithecinae.
Taxonomic classification
Allen's swamp monkey belongs to the monophlyetic genus Allenopithecus. It is a basal member of Cercopithecini, as it was one of the first lineages to diverge from the ancestral stock at about 7 million years ago.[3] It is named after Joel Asaph Allen.[4] Other common names include the swamp guenon, the blackish-green guenon, and Allen's baboon-like monkey.[5]: 652 Whether or not Allen's swamp monkey can be classified as a guenon depends whether the term "guenon" is applied to members of Cercopithecus or to members of Cercopithecini.[6]
Changes in taxonomy
Allen's swamp monkey was first described by Reginald Innes Pocock as Cercopithecus nigroviridis in a 1907 revision of Cercopithecus. He placed the species in his æthiops group while noting that further taxonomic refinement may have been necessary to emphasize the morphological differences between Allen's swamp monkey and other members of the group.[7] This arrangement followed the precedent of Philip Sclater's taxonomy, which organized Cercopithecus into species groups based on pelage alone, with æthiops corresponding to Sclater's green guenon group, chloronoti.[8] The holotype used by Pocock is the skin of a subadult female from the upper Congo River that lived in the London Zoo between 1892 and 1894.[7] Pocock erroneously described Allen's Swamp Monkey as being similar in size to talapoins as a result of the immaturity of the holotype. Daniel Giraud Elliot published a competing taxonomy in his 1913 Review of the Primates, with Allen's swamp monkey described as Lasiopyga nigriviridis [sic] based on the holotypic specimen.[5]: 652 The American Museum of Natural History's acquisition of an adult male specimen that was shot on an island near Bolobo in 1909 allowed for Herbert Lang to move the species to a monophyletic genus, Allenopithecus, in 1923.[9] Lang's revision addressed the more robust habitus of the adult specimen compared to Pocock's subadult holotype.[9] This rearrangement would be omitted from subsequent reviews of African monkeys until Ernst Schwarz published data acquired from live individuals at the Berlin Zoo in 1928.[8]
In 1987, Elizabeth Strasser and Eric Delson proposed designating Allen's swamp monkey as a member of a monophyletic subtribe, Allenopithecina, to acknowledge its primitive characteristics within the context of cercopithecins. They identified the species' suite of papionine traits as symplesiomorphies resulting from its primitive status within Cercopithecinae.[10] Colin Groves published an alternative taxonomy in 1989 that described Allen's swamp monkey as a papionin due to its morphological similarities to other members of the tribe. Like subsequent taxonomies, Groves' framework characterized A. nigroviridis as a basal member of its tribal taxon due to its primitive somatic number of 2n = 48.[11] Groves later revisited the species and instead classified A. nigroviridis as belonging to a sister taxon to Cercopithecini and Papionini, rather than being a member of one or the other. A Y-chromosome analysis published by Anthony Tosi et al. in 2002 responded to Groves' and Strasser's taxonomies, and agreed with the latter by characterizing Allen's swamp monkey as a primitive cercopithecin, albeit without ascribing it membership to a monophyletic subtribe.[12]
Description
Allen's swamp monkey has an overall guenon-like appearance, but also possesses traits reminiscent of papionins,[5]: 177 It has a stocky, robust build,[5]: 624 [13] differing from the typically gracile bodies of other cercopithecins.[14] The adult body ranges between 45 and 60 cm (18 and 24 in).[citation needed] The tail is only slightly longer than the head-body length, which is derived from a longer, ancestral form that is still exhibited by extant guenons.[8] Males, weighing up to 6.0 kg (13.2 lb), are substantially larger than the females, which only weigh up to 3.7 kg (8.2 lb).[13] The skeleton is generalized so as to facilitate both arboreal and terrestrial locomotion.[14] With the exception of the free thumb, the fingers are webbed between the proximal phalanges, which may be an adaptation to a palustral lifestyle.[8] The quadrupedal standing posture resembles that of a baboon, with the thumb and index finger articulated independently from the other three digits.[5]: 650
The facial skin is darkly pigmented except for the pale cheeks.[7] The ears are pointed, resembling those of a macaque rather than a cercopithecin.[8] Adult females retain sparse black cilia as remnants of the long silky eyelashes of the fetal form, whereas in adult males such features are absent.[8] The top of the braincase is flat, with the exception of a sagittal crest in males.[9] The adult brain weighs 1⁄51 the body weight.[5]: 649 The permanent dental formula is 2.1.2.32.1.2.3 × 2 = 32. The incisors, canines, and lower molars resemble those of guenons, notwithstanding an absent cusp in M3, while the upper molars are robust and papioine.[9] As a cercopithecine, Allen's swamp monkey possesses a pair of cheek pouches that it can access through slit-like openings near the molars. The snout is more prominent in males than in females.[8] The cercopithecine air sac of the respiratory tract is large, such that it extends above the suprasternal notch subcutaneously.[5]: 43,642 The female nipples are positioned close together, which allows an infant to suckle from both simultaneously.[8] Unlike most other cercopithecins, female Allen's swamp monkeys exhibit sexual swelling during estrus.[5]: 134,177 Ischial callosities are present in both sexes, and males exhibit individual variation in the shapes and sizes of their callosities.[8] Males have relatively large testes for cercopithecins,[5]: 644 and the scrotum is pale blue.[9]
The pelage is coarse,[9] and consists of gray, green, and yellow shades, with a lighter, grayish-brown agouti layer at the base of the hairs. The whiskers are olivaceous and are angled dorsally across the face. The neck, back, shoulders, and the top of the head have yellowish tinges, while the chin, neck, chest, abdomen, and inner limbs are pale. The tail is darker than the rest of the coat, especially near the tip, and it is yellow at the base and on the underside.[7] The newborn pelage resembles that of the adult, although the yellow hues are more pronounced, and a crown consisting of silky white hairs is present. The natal coat is fully replaced by 10 weeks of age.[15]
Behavior
Allen's swamp monkey is a diurnal animal and regularly looks for food on the ground. It inhabits swampy, water-rich areas and can swim well, diving to avoid danger.
Allen's swamp monkey lives in multimale-multifemale groups[6] of up to 40 individuals. The number of males in a group depends on the number of females, such that smaller groups are likely to contain only one adult male. Despite this demographic pattern, males are not known to live solitarily, indicating that external factors may influence the relationship between group size and adult male presence.[16] The sizes and sexual compositions of groups imitate those of papionins, however the rarity with which members of opposite sexes interact is a guenon trait. This idiosyncratic social organization could be a result of Allen's swamp monkey's basal position within Cercopithecini.[12]
Its diet consists of fruits and leaves, as well as beetles and worms.
Little is known about the mating habits of this species. The females bear young, which are weaned around three months old and are mature after three to five years. Its lifespan can be as long as 28 years.[17] Raptors, and snakes are the natural predators of Allen's swamp monkey. It is also hunted for its meat.
Range
Allen's swamp monkey lives in the Congo Basin between 16°E and 24°E, and 4°N and possibly 6° S.[2] Its range includes the Republic of Congo, the Democratic Republic of Congo,[17][18] and possibly Cameroon, with one documented sighting in the Central African Republic.[2] Prior to the 1990s, its range was believed to be limited to the swamps and riparian forests adjacent to the lower Likouala-aux-Herbes, Oubangui, and Sangha rivers, however a discontinuous population was confirmed in the upper Sangha in 2006, about 100 km (62 mi) northwest of its previously recognized range.[19] It was recorded from Dzanga-Sangha Special Reserve in the Central African Republic in 2016.[2] Because of its riparian habit, rivers are less likely to be geographic barriers that affect the species' range than they are for sympatric primates.[20]
References
- ↑ Groves, C. P. (2005). "Order Primates". In Wilson, D. E.; Reeder, D. M (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. 153. ISBN 978-0-8018-8221-0. OCLC 62265494.
- 1 2 3 4 Maisels, F.; Mittermeier, R.A.; Oates, J.F.; Hart, J. (2020). "Allenopithecus nigroviridis". IUCN Red List of Threatened Species. 2020 e.T865A166606573. doi:10.2305/IUCN.UK.2020-1.RLTS.T865A166606573.en. Retrieved 19 November 2021.
- ↑ Perelman, P.; Johnson, W.E.; Roos, C.; Seuánez, H.N.; Horvath, J.E.; Moreira, M.A.M.; Kessing, B.; Pontius, J.; Roelke, M.; Rumpler, Y.; Schneider, M.P.C.; Silva, A.; O'Brien, S.J.; Pecon-Slattery, J. (17 March 2011). "A Molecular Phylogeny of Living Primates". PLOS Genetics. 7 (3) e1001342. doi:10.1371/journal.pgen.1001342. PMC 3060065. PMID 21436896.
- ↑ Beolens, Bo; Watkins, Michael; Grayson, Michael (2009). The Eponym Dictionary of Mammals. Johns Hopkins University Press. p. 8. ISBN 978-0-8018-9533-3.
- 1 2 3 4 5 6 7 8 9 Hill, W.C.O. (1966). Primates: Comparative Anatomy and Taxonomy. New York: John Wiley & Sons, Inc. pp. 43, 134, 177, 624, 641–642, 644, 649, 650–652. Retrieved 28 July 2026.
- 1 2 Butynski, T.M. (2004). "The Guenons: An Overview of Diversity and Taxonomy". In Glenn, M.E.; Cords, M. (eds.). The Guenons: Diversity and Adaptation in African Monkeys. Boston, MA: Kluwer Academic Publishers. pp. 3–13. ISBN 978-0-306-48417-9. Retrieved 30 July 2026.
- 1 2 3 4 Pocock, R.I. (18 June 1907). "A monographic revision of monkeys of the genus Cercopithecus". Proceedings Of The General Meetings For Scientific Business Of The Zoological Society Of London: 679, 725–726, 739–740. Retrieved 28 July 2026.
- 1 2 3 4 5 6 7 8 9 Hill, W.C.O. (1964). "XXI.—The External Anatomy of Allenopithecus". Proceedings of the Royal Society of Edinburgh. Section B. Biology. 68 (4): 302–326. doi:10.1017/S0080455X00001120.
- 1 2 3 4 5 6 Lang, Herbert (12 September 1923). "A new genus of African monkey, Allenopithecus". American Museum Novitates. 87.
- ↑ Strasser, E.; Delson, E. (January 1987). "Cladistic analysis of cercopithecid relationships". Journal of Human Evolution. 16 (1): 81–99. doi:10.1016/0047-2484(87)90061-3.
- ↑ Groves, C.P. (1989). A Theory of Human and Primate Evolution. New York: Oxford University Press. p. 134. ISBN 0198576293.
- 1 2 Tosi, A.J.; Buzzard, P.J.; Morales, J.C.; Melnick, D.J. (December 2002). "Y-chromosome Data and Tribal Affiliations of Allenopithecus and Miopithecus". International Journal of Primatology. 23 (6): 1287–1299. doi:10.1016/0047-2484(87)90061-3.
- 1 2 Rowe, N.; Goodall, J. (1999). The pictorial guide to the living primates (2nd ed.). Charlestown, Rhode Island: Pogonias Press. p. 147. ISBN 0-9648825-1-5.
- 1 2 Lo Bianco, S.; Masters, J.C.; Sineo, L. (November 2017). "The evolution of the Cercopithecini: a (post)modern synthesis". Evolutionary Anthropology: Issues, News, and Reviews. 26 (6): 336–349. doi:10.1002/evan.21567.
- ↑ Pournelle, G.H. (29 May 1962). "Observations on the Birth and Early Development of Allen's Monkey". Journal of Mammalogy. 43 (2): 265–266. doi:10.2307/1377104.
- ↑ Cords, M. (2000). "The Number of Males in Guenon Groups". In Kappeler, P.M. (ed.). Primate Males: Causes and Consequences of variation in group composition. Cambridge: Cambridge University Press. p. 90. ISBN 9780521658461.
- 1 2 "Allen's swamp monkey". Smithsonian's National Zoo. 2016-04-25. Retrieved 2023-09-12.
- ↑ "Allen's Swamp Monkey Characteristics | Allenopithecus nigroviridis Facts". Bio Explorer. Retrieved 2023-09-12.
- ↑ Maisels, F.; Blake, S.; Fay, M.; Mobolambi, G.; Yako, V. (August 2006). "A Note on the Distribution of Allen's Swamp Monkey, Allenopithecus nigroviridis, in Northwestern Congo". Primate Conservation. 21: 93–95. doi:10.1896/0898-6207.21.1.93.
- ↑ Colyn, M.; Deleporte, P. (2004). "Biogeographic Analysis of Central African Forest Guenons". In Glenn, M.E.; Cords, M. (eds.). The Guenons: Diversity and Adaptation in African Monkeys. Boston, MA: Kluwer Academic Publishers. p. 69. ISBN 978-0-306-47346-3. Retrieved 30 July 2026.
