Name: Mesopropithecus.
Phonetic: Me-sp-pro-pif-e-cus.
Named By: Herbert F.‭ ‬Standing‭ ‬-‭ ‬1905.
Synonyms: Neopropithecus.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Primates,‭ ‬Strepsirrhini,‭ ‬Lemuriformes,‭ ‬Palaeopropithecidae.
Species: M.‭ ‬pithecoides,‭ ‬M.‭ ‬dolichobrachion,‭ ‬M.‭ ‬globiceps.
Diet: Herbivore.
Size: Between‭ ‬10‭ ‬and‭ ‬14‭ ‬kilograms depending upon species‭ ‬-‭ ‬refer to main text.
Known locations: Across Madagascar,‭ ‬nut different species inhabited different areas‭ ‬-‭ ‬refer to main text.
Time period: Pleistocene to Holocene,‭ ‬as recently as‭ ‬570-679‭ ‬CE.
Fossil representation: Several skulls and now post cranial remains as well.

       Mesopropithecus is currently the smallest of the known sloth lemurs although originally it was thought to have been similar to today‭’‬s modern‭ ‬indriid lemurs,‭ ‬an idea based upon comparison between the known skulls.‭ ‬In‭ ‬1986‭ ‬however,‭ ‬post cranial remains were found and attributed to the genus and immediately the key feature of a forelimb much longer than a rear limb was identified,‭ ‬something that indicated Mesopropithecus was a sloth lemur.‭ ‬With this in mind it‭’‬s possible that Mesopropithecus might represent a more primitive form of sloth lemur that the more specialised genera evolved from.‭ ‬Even if this is true however we do know that Mesopropithecus likely lived alongside other more specialised sloth lemurs until they all went extinct within a few centuries of one another.‭ ‬This extinction is thought to have been down to the combined effects of human hunting and habitat loss through human activities.

       Mesopropithecus has been classed as a sloth lemur because the forelimbs are proportionately longer than the rear limbs which indicate that Mesopropithecus relied upon these limbs to reach out and pull itself along branches.‭ ‬Indriid lemurs by contrast have longer hind limbs which they use to leap from branch to branch.‭ ‬Mesopropithecus however was a climber that would either walk across branches or hang from underneath them,‭ ‬an ability that was helped by skeletal adaptations that would allow it to travel this way.‭ ‬This more sedentary lifestyle would also require less energy than the more active indriids,‭ ‬which explains why Mesopropithecus and particularly some related sloth lemurs grew so large,‭ ‬since the energy it acquired from its food was used to sustain its body rather than move around.‭ ‬Mesopropithecus had a robust physique to deal with this size and weight to the point that it looks like a more heavily built indriid.‭ ‬This is why Mesopropithecus is considered to be somewhere in between since it‭’‬s too heavily built to be an indriid,‭ ‬while not as robust as other more specialised sloth lemurs.
       There is some confusion regarding the lower jaw dental formula of Mesopropithecus‭ (‬a problem shared by other sloth and indriid lemurs‭)‬.‭ ‬One of the teeth is either an incisor or a canine although it is exceedingly difficult to make a clear distinction between the two types.‭ ‬This means that the lower jaw dental formula for Mesopropithecus is either‭ ‬‭ (‬one incisor,‭ ‬one canine,‭ ‬two premolars,‭ ‬three molars‭) ‬or‭ ‬‭ (‬two incisors,‭ ‬no canines,‭ ‬2‭ ‬premolars,‭ ‬three molars‭)‬.‭ ‬When combined with the upper dental formula of‭ ‬‭ ‬however,‭ ‬both lower dental formulas add up to‭ ‬a‭ ‬total of thirty teeth in the mouth.‭ ‬The four frontal teeth are also arranged in a form of tooth comb as a feeding adaptation.‭ ‬Mesopropithecus is usually depicted as a folivore‭ (‬an eater of leaves‭)‬,‭ ‬but is also thought to have eaten fruits and seeds as well,‭ ‬the latter to the point of Mesopropithecus being described as a‭ ‘‬seed predator‭’‬,‭ ‬an animal that makes special effort to eat seeds while often leaving other edible parts untouched.
       There is obviously some variation between the remains of different Mesopropithecus species,‭ ‬but they can also be arranged by estimated weight and known geographical range of sub fossil remains.‭ ‬The table below provides a simple overview of this information.

Comparison and overview of Mesopropithecus species.
Species Named by/Date Weight in kilograms Fossil distribution in Madagascar Estimated extinction date
M. dolichobrachion Simons et al. - 1995 14kg Far North 570-679 CE
M. globiceps Lamberton - 1936 11kg Central areas 245-249 CE
M. pithecoides Standing - 1905 10kg South west Unavailable

       Other known sloth lemurs include Palaeopropithecus,‭ ‬Archaeoindris and Babakotia,‭ ‬the latter one thought to be closest to Mesopropithecus while the first two are considerably bigger.


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