Micodon

Micodon is an extinct genus of New World monkeys from the Middle Miocene (Laventan in the South American land mammal ages; 13.8 to 11.8 Ma). Its remains have been found at the Konzentrat-Lagerstätte of La Venta in the Honda Group of Colombia. The type species is "M. kiotensis", a very small monkey among the New World species.
Description.
Fossils of "Micodon" were discovered in the La Victoria Formation, that has been dated to the Laventan, about 13.5 Ma. "Micodon" is the smallest primate found in the La Venta fauna, and within size range of "Saguinus" and "Callithrix". It differs from most callitrichines in the generally low-relief morphological pattern, large size of the talon basin, and particularly, the considerably large size of hypocone. The morphology and position of the hypocone is distinctly different from the conditions found in such genera as "Callimico" and "Saimiri". By comparison with "Micodon", the hypocone is far smaller in "Callimico", where it appears as an excrescence of the lingual cingulum. This cusp is more developed in "Saimiri". Overall, the "Micodon" M1 shows some gross resemblances to certain "Saguinus", although none of the specimens examined hardly approach this fossil in hypocone development.
"Micodon" is clearly within the size range of living marmosets but is well below the size range of larger marmosets, such as "Callimico goeldii" and "Leontopithecus chrysopygus". Since the callitrichines are probably a modified radiation that underwent their major diversification at a small body size, it is considered very likely that "Micodon" is a marmoset. The "Micodon" 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" and "Saimiri", 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. 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, the Late Eocene "Perupithecus" from the Peruvian Amazon.
It has been suggested the specimens ascribed to "Micodon", smaller than "Aotus dindensis", may actually be deciduous teeth of another primate species found at La Venta such as "Saimiri annectens" or "S. fieldsi". More material is needed for a better description of the genus.
A body mass of has been estimated for "Micodon".
Habitat.
The Honda Group, and more precisely the "Monkey Beds", are the richest site for fossil primates in South America. From the same level as where "Micodon" has been found, also fossils of "Cebupithecia", "Mohanamico", "Saimiri annectens", "Saimiri fieldsi" and "Stirtonia" have been uncovered. It has been argued that the monkeys of the Honda Group were living in habitat that was in contact with the Amazon and Orinoco Basins, and that La Venta itself was probably seasonally dry forest. The evolutionary separation from "Aotus" of "Micodon" has been placed in the Early Miocene at 17.5 Ma.