| Homunculus | |
|---|---|
 | |
| Fossil skull ofHomunculus patagonicus, scale bar = 1 centimetre (0.39 in) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Parvorder: | Platyrrhini |
| Genus: | †Homunculus Ameghino, 1891 |
| Type species | |
| Homunculus patagonicus Ameghino, 1891 | |
| Other Species | |
Homunculus vizcainoi Kay & Perry, 2019[1] | |
| Synonyms[2] | |
Synonyms ofH. patagonicus
| |
Homunculus (Latin:[hɔˈmʊŋkʊlʊs]; "little person") is an extinct genus ofNew World monkey that lived inPatagonia during theMiocene. Two species are known:Homunculus patagonicus[3][2][4] andHomunculus vizcainoi, which are known from material found in theSanta Cruz Formation in the far south ofArgentina.[1] Reaching a latitude of ~55°S at the time it lived, it is the southernmost non-human primate ever recorded.[5]
Theholotype ofHomunculus patagonicus (MACN-A 634), a partial skull, was discovered around theRío Gallegos, though more specific details of its provenance have never been given.[2] It is likely, from its location, that the holotype originates from strata belonging to theSanta Cruz Formation.[1] At some point prior to 1891, it entered the collection of palaeontologistCarlos Ameghino and in that year it was described by his brother,Florentino.[6] At some point, MACN-A 634 was lost. It was, in 2008, replaced with a neotype, MACN-A 575.[2] A secondHomunculus,H. vizcainoi, also from the Santa Cruz Formation, was described in 2019.[1]
In the same year as Florentino Ameghino's paper, Swiss geologist and palaeontologist Alcides Mercerat described an incomplete mandibular fragment, bearing part of amolar. He dubbed the specimenEcphantodon ceboides.[7] However,E. ceboides was treated by Ameghino as indistinguishable fromHomunculus, and he opted to synonymise the two. The type specimen ofE. ceboides has been lost.[2] In the paper describingH. patagonicus, Florentino Ameghino also namedAnthropops perfectus, which he distinguished based on purported characteristics of the mandible and lowercanine, andPitheculus australis. In 1894, he namedStilotherium grande, which he suggested to be amarsupial.[8] However, subsequent authors, likeOsvaldo A. Reig, disagreed with this assessment,[9] and 1981, Philip Hershkovitz determined that it belonged toHomunculus. Hershkovitz erected a new species,H. grandis.[10] Even in the absence of the holotype, further specimens have been assigned toH. patagonicus. Notable among these is MACN-A 5968, the left side of a partial skull, recovered from Puesto Estancia La Costa.[2] In 2008, a genus-level revision ofHomunculus was carried out, whereupon it was concluded thatAnthropops,Pitheculus andStilotherium were all junior synonyms ofHomunculus.[2] Some authors considerKillikaike blakei to be a junior synonym forH. patagonicus,[11][1] but others consider the species distinct.[12] A 2025 study of an associated skeleton ofHomunculus again concluded thatKillikaike is a junior synonym ofHomunculus patagonicus.[5]
Some studies have regardedHomunculus as acrown group platyrrhine and a member of the familyPitheciidae, possibly belonging to a tribe of its own (Homuncilini),[2] while other studies have regarded it as a stem-group platyrrhine outside any modern group. The latter is supported by the morphology of itsnasal turbinates, which are dissimilar to those of crown-group platyrrhines.[13]
H. patagonicus was a robustly built, quadrupedal primate, with body mass estimates varying between 1.4 and 5.9 kg (3.1 and 13.0 lb) based on different techniques,[14] with a 2025 study estimating a body mass of around 2 kilograms (4.4 lb), comparable to atiti monkey or asaki monkey.[5] The interorbital region, the portion of the skull between theorbits (eye sockets) was wide, similar to intiti monkeys (Callicebinae). Thefrontal bone was unvaulted, unlike moderncapuchin monkeys (Cebinae). Themaxillary sinus was relatively large, and thenasals were quite wide. Thepremaxilla was fairly procumbent. The main body of themandible, the corpus, was deeperposteriorly (towards the rear), similar to indouroucoulis (Aotus). The tooth rows convergedanteriorly (towards the front). Theincisors were narrow and fairly high crowned. The secondpremolar is wedge-shaped, compressedtransversely (across) and has a large honing facet (wear pattern) from the uppercanine. Themolars have fairly longtalonids, and thetrigonids were short, especially in the first molar.[2] The postcrania have a few attributes indicating a relatively basal position, such as the form of its nasal turbinates[13] and anepidoncylar foramen. Theradius was similar to modern cebids, and could rotate freely.[15]
Its morphology suggests thatHomunculus was adiurnal (day active)arboreal primate that spent a significant amount of time climbing and clinging to trees, probably occasionally leaping between them.[5] Although one study suggested that it was primarilyfrugivorous based on dental wear,[16] this has been disputed, and other studies suggest the diet ofHomunculus likely consisted of fruit, leaves and seeds, including relatively hard items, with the significant input of abrasive volcanic dust into the environment of the Santa Cruz Formation being the likely cause of the heavy tooth wear observed in adultHomunculus teeth.[5] TheSanta Cruz Formation in whichHomunculus has been found, and from which the remains of many other species of prehistoric animal have been uncovered, is thought to have been relatively warm and humid, including a mix of opensavanna,gallery forests and semi-deciduous forests.[17]
