| Micodon | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Infraorder: | Simiiformes |
| Family: | Callitrichidae |
| Genus: | †Micodon Setoguchi & Rosenberger1985[1] |
| Species: | †M. kiotensis |
| Binomial name | |
| †Micodon kiotensis Setoguchi and Rosenberger 1985 | |
Micodon is anextinctgenus ofNew World monkeys from theMiddle Miocene (Laventan in theSouth American land mammal ages; 13.8 to 11.8 Ma). Its remains have been found at theKonzentrat-Lagerstätte ofLa Venta in theHonda Group ofColombia. Thetype species isM. kiotensis,[2] a very small monkey among the New World species.[3]
Fossils ofMicodon were discovered in theLa Victoria Formation, that has been dated to theLaventan, about 13.5 Ma.Micodon is the smallest primate found in the La Venta fauna, and within size range ofSaguinus andCallithrix. It differs from most callitrichines in the generally low-relief morphological pattern, large size of the talon basin, and particularly, the considerably large size ofhypocone. The morphology and position of the hypocone is distinctly different from the conditions found in such genera asCallimico andSaimiri. By comparison withMicodon, the hypocone is far smaller inCallimico, where it appears as an excrescence of the lingual cingulum. This cusp is more developed inSaimiri. Overall, theMicodon M1 shows some gross resemblances to certainSaguinus, although none of the specimens examined hardly approach this fossil in hypocone development.[4]
Micodon is clearly within the size range of livingmarmosets but is well below the size range of larger marmosets, such asCallimico goeldii andLeontopithecus chrysopygus. Since the callitrichines are probably a modified radiation that underwent their major diversification at a small body size, it is considered very likely thatMicodon is a marmoset. TheMicodon M1 suggests that body size/tooth size reduction preceded the loss of the hypocone cusp. It has been argued that the combination of tricuspid molars and small size literally define a marmoset phyletically. On the other hand,Callimico is a four-cusped ceboid whose anatomy suggests that it is cladistically closest to the tricuspid marmosets, and alternative schemes of platyrrhine phylogeny place the four-cusped cebines,Cebus andSaimiri, as the sister-taxon of the entire group. The upshot of these latter views is that a four-cusped molar would be fully expectable in small, ancestral callitrichine, and even in callitrichin sister-group.[5] The upper first molar (M1) with a subtriangular outline with a narrow lingual side resembles that of the oldest New World primate discovered to date, theLate EocenePerupithecus from the Peruvian Amazon.[6]
It has been suggested the specimens ascribed toMicodon, smaller thanAotus dindensis,[7] may actually be deciduous teeth of another primate species found at La Venta such asSaimiri annectens orS. fieldsi.[8] More material is needed for a better description of the genus.[9]
A body mass of 400 grams (0.88 lb) has been estimated forMicodon.[10]
The Honda Group, and more precisely the "Monkey Beds", are the richest site forfossil primates in South America.[11] From the same level as whereMicodon has been found, also fossils ofCebupithecia,Mohanamico,Saimiri annectens,Saimiri fieldsi andStirtonia have been uncovered.[12][13] It has been argued that the monkeys of the Honda Group were living in habitat that was in contact with theAmazon andOrinoco Basins, and that La Venta itself was probably seasonally dry forest.[14] The evolutionary separation fromAotus ofMicodon has been placed in the Early Miocene at 17.5 Ma.[15]
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