Aotus trivirgatus, the owl monkey, is a South American or New World monkey. South American monkeys or platyrrhines comprise one of the two infraorders (Platyrrhini and Catarrhini) of anthropoid primates. They live exclusively in South and Central America, but their fossil distribution includes the Greater Antilles (MacPhee and Horovitz, 2002). The fossil record of platyrrhines extends back to the Deseadan or late Oligocene of Bolivia where they are represented by the genus Branisella (Takai & Anaya, 1996). Their presence in the New World is generally considered to be the result of a single dispersal event (Fleagle, 1999) near the end of the Eocene from the Old World, where all known basal anthropoids are found (Beard, 2002). Because South America was not connected with North America or Africa at the time, this dispersal must have involved rafting across some portion of the Atlantic.

Once in the New World, platyrrhines diverged into a variety of forms ranging in size from the smallest living anthropoid (Cebuella) at ~110 grams to the howler monkeys (Alouatta) that reach 11 kg (Fleagle, 1999). This diverse radiation of primates includes 78 living species (Fleagle, 1999) in 16 genera, one of which is the only living nocturnal anthropoid, Aotus. Their diets and locomotor adaptations are diverse, though most are at least partly frugivorous and none are primarily terrestrial.

Although the adaptations of different genera are reflected in their craniodental anatomy, platyrrhines in general retain a cranial morphology more similar to primitive anthropoids from the Eocene and Oligocene of Egypt such as Catopithecus, Parapithecus, and Aegyptopithecus than do the living Old World anthropoids (Fleagle, 1999; Simons, 2001). The research for which these CT data were collected indicates that this primitive anthropoid cranial morphology included considerable cranial pneumatization via the paranasal sinuses.

Aotus trivirgatus is the only nocturnal anthropoid and is rather small with males and females averaging 813g and 736g respectively (Fleagle, 1999). Its orbits are the largest of any anthropoid, housing the enlarged eyes that give them effective night vision. Like Callicebus, they are monogamous and mainly frugivorous. Although sometimes grouped with Callicebus in their own subfamily, the Aotinae (e.g., Fleagle, 1999), Aotus may be more closely related to Saimiri, Cebus, and the marmosets and tamarins (callitrichines) (Horovitz, 1999; von Dornum and Ruvolo, 1999).

This female specimen, the skull of a juvenile (M1 not fully in place), was obtained from Pet Farm Inc. in Miami, Florida. The occipital region of the skull is cut away. It was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Dr. James Rossie of Stony Brook University, courtesy of the Smithsonian Institution Division of Mammals. Scanning was funded by an NSF dissertation improvement grant to Mr. Rossie (#0100825). Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

lateral view

ventral view

This specimen was scanned by Matthew Colbert on 11 March 2002 along the coronal axis for a total of 565 slices. Each slice is 0.0967 mm thick, with an interslice spacing of 0.0967 mm and a field of reconstruction of 41.0 mm.

Literature
Beard, K. C. 2002. Basal anthropoids. In (W. C. Hartwig, Ed) The Primate Fossil Record, pp. 133-149. Cambridge, Cambridge University Press.

Fleagle, J. G. 1999. Primate Adaptation and Evolution. San Diego, Academic Press.

Horovitz, I. 1999. A phylogenetic study of living and fossil platyrrhines. American Museum Novitates 3269:1-40.

MacPhee, R. D. E. and I. Horovitz. 2002. Extinct Quaternary platyrrhines of the Greater Antilles and Brazil. In (W. C. Hartwig, Ed) The Primate Fossil Record, pp. 189-200. Cambridge, Cambridge University Press.

Simons, E. L. 2001. The cranium of Parapithecus grangeri, and Egyptian Oligocene anthropoidean primate. Proceedings of the National Academy of Sciences, USA 98:7892-7897.

Takai, M. and F. Anaya. 1996. New specimens of the oldest fossil platyrrhine, Branisella boliviana, from Salla, Bolivia. American Journal of Physical Anthropology 99:301-317.

von Dornum, M. and M. Ruvolo. 1999. Phylogenetic relationships of the New World monkeys (Primates, Platyrrhini) based on nuclear G6PD DNA sequences. Molecular Phylogenetics and Evolution 11:459-476.

Links
Aotus trivirgatus on the Animal Diversity Web (University of Michigan Museum of Zoology)

Aotus trivirgatus on the Primate Info Net (University of Wisconsin, Madison)

The brain of Aotus trivirgatus on the Comparative Mammalian Brain Collections

Face slice movie: