The odd importance of primates in Madagascar

(writing in progress)

One of the oddest features of mammalian biogeography is the prominence of primates in Madagascar. I’d like to explore this topic w.r.t. two aspects, namely a) body size, b) terrestriality, and c) comparison with the Americas.
 
The extant and extinct fauna of primates in Madagascar is bewilderingly diverse, so let me focus on one particularly noteworthy form, Archaeoindris. This, the largest of all lemurs (about the same size as gorillas), was among the largest primates ever to have evolved.
 
Large size suggests terrestriality in primates, but even some of the monkey-size lemurs were terrestrial, e.g. Hadropithecus (please see screenshot below).
 
Although primates are diverse in the Neotropics, and monkeys formerly occurred in the Antilles, there have never been large primates (body mass >25 kg) or terrestrial primates in the Americas. I suppose that this is because the niche of larger terrestrial omnivore was taken by Xenarthra there.
 
No extant monkey in the Americas is as terrestrial even as a vervet monkey (Chlorocebus). And there is nothing, extant or extinct, in the American primates anything like the baboons or geladas, or even the Asian macaques (which show a baboon-like trend towards large body size and terrestriality but do not take this trend to the extremes seen in Africa).
 
So it’s odd that both Africa and Madagascar, in their own ways, feature primates so prominently, with large and terrestrial primates playing prominent ecological roles. The Americas are quite different, because although primates have lived there since the time of the dinosaurs there has never been any evolution of terrestrial or large primates in North America, central America, South America, or the Antilles. For example, the Pampas was a paradise for grazers, but it never featured any mammal even vaguely like the geladas, those grazing large monkeys of Africa.
 
The niche of gelada (Africa) or giant/terrestrial lemur (Madagascar) seems to have been occupied in the Americas by sloths (Xenarthra) rather than by primates. This is not a case of particular evolutionary convergence because sloths are so different from monkeys and lemurs. For example, sloths have ever-growing teeth and use long claws; and whereas even primitive primates such as lemurs are above the mammalian average in braininess the sloths are below the mammalian average in braininess.
 
It’s well-known that Australasia lacked primates, having marsupials (e.g. possums) in vaguely similar niches to those of small primates. However, it’s less well-known that the Americas – despite their bewildering diversity of small monkeys today – have always lacked large or terrestrial primates, even in the times of the Pleistocene megafauna.
 
And Madagascar really is most peculiar, because not only is the extant fauna rich in primates but the extinct fauna was even richer – extending to extremely large species as well as probably terrestrial ones, most comparable to ground sloths.
  
Re Archaeoindris:
https://en.wikipedia.org/wiki/Archaeoindris
 
https://en.wikipedia.org/wiki/Subfossil_lemur
 
re terrestriality in Hadropithecus, which was not particularly large but foraged on graminoids and tubers:
https://en.wikipedia.org/wiki/Monkey_lemur

(writing in progress)

Publicado el 29 de junio de 2022 por milewski milewski

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