Micropithecus

Micropithecus Temporal range:Miocene ~
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Suborder:	Haplorhini
Infraorder:	Simiiformes
Parvorder:	Catarrhini
Genus:	†Micropithecus Fleagle & Simons, 1978
Species
†M. clarki(Fleagle & Simons, 1978) †M. leakeyorum(Harrison, 1989) †M. chamtwaraensis(Pickford et al., 2021)

Micropithecusis an extinctgenusofprimatesthat lived inEast Africaabout 19 to 15 million years ago, during the earlyMiocene.The genus and itstype species,Micropithecus clarki,were first scientifically described in 1978.

Naming

The generic name,Micropithecus,is derived from theGreekWords μικρός (ancient Greekpronouncedmikrós,"small" ) and πίθηκος (pronouncedpíthēkos,"monkey" ).Micropithecusthus means "small ape", referring to the fact that thefossilsof this genus are among the smallest fossil apes discovered.

History of description

Theholotypeof both the genus and type species,Micropithecus clarki,is anupper jaw,which is approximately 19 to 17 million years old, with largely preservedpalatebones, and remains of bones of theskull.Also preserved in the upper jaw are three left large molars (M1 - M3), as well as onepremolar,and three large molars (M1 - M3) on the right side. In addition, about 20 individually found teeth, amandiblefragment and fragments of a skull dome from the same locality were designated asparatypes.

Micropithecuswas distinguished fromLimnopithecus,Dendropithecus,DryopithecusandPliopithecusby the characteristics of its dentition and its small size. Furthermore, in the initial description of the genus and type species, it was pointed out that themorphologyof the face of these fossil finds most closely resemblesgibbonsliving today. The head-torso length is roughly equivalent to thewhite-fronted capuchin monkeys,which are only about 35 centimetres tall, and is slightly smaller than that of the fossil ofAeolopithecus,now considered a junior synonym ofPropliopithecus.

Further finds

In 1989, a second species was attributed to the genusMicropithecus,Micropithecus leakeyorum.These are finds from theMaboko Mainexcavation site onMaboko IslandinLake Victoria,Kenya,dating from 16 to 15 million years ago. This species was placed in the genusMicropithecusbased on several mandibular fragments with preserved large molars and on the basis of the characteristics of these teeth, but at the same time it was distinguished from the type species because of the spatial and temporal distance.

In 2021, as part of a revision of the small-bodied anthropoids from Kenyan sites, some finds placed since 1982 withMicropithecus clarkiwere separated from them asMicropithecus chamtwaraensis;the epithet,chamtwaraensis,refers to the name of theChamtwara Formation(seeList of fossiliferous stratigraphic units in Kenya) in the area of 'Site 34' near the locality ofKoru.The holotype is a largely preserved dentate mandible (archive number KNM CA 380).

Palaeoecology

In the first description ofMicropithecus leakeyorum,it was discussed that there is no other example in East Africa in the Miocene besidesNyanzapithecusandMicropithecusfor a genus of primates existing over several million years whose species could be documented in chronological succession. However, it cannot be concluded from this sequence that the younger species evolved from the older one. The preserved remains ofMicropithecus clarkishow numerousoriginal featuresof theOld World monkey,but also variousyounger features,such as relatively small molars in relation to the jawbone and very large incisors compared to the molars; features that overall suggest afruit-rich diet.Micropithecus leakeyorumalso has features indicative of a fruit-rich diet, but these features are less pronounced than in its older sister species. This has been interpreted as a presumed consequence of less specialisation on a particular diet, giving this species a morphological proximity to the more primitive, much older, Old World monkeys from East Africa.

An explanation for these different characteristics can be found if one considers thepalaeoecology:About 19 million years ago, what is nowUgandaand western Kenya were predominantly covered by forests, fostered by a warm and humidtropicalclimate.Later, the climate in this region changed and the forests became thinner and drier. The cause of these changes was probably tectonic processes, which also had a local influence on the extent of precipitation. For the excavation sites on Maboko Island, detailed studies of theplant worldhave shown that open, sparsely forested landscapes existed there in the Middle Miocene with densegallery forestsalong the rivers, comparable to thevegetationof today'sNyika National Park.In suchbiotopes,it was concluded, the ancestors ofMicropithecus leakeyorumgradually adapted to a broader diet that included harder plant fibres.