All-new movies and applet added July 2012!

Alouatta seniculus, the red howler, is a South American or New World monkey. South American monkeys or platyrrhines comprise one of the two infraorders (Platyrrhini & 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 and 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.

Alouatta seniculus is one of the smaller atelines with males and females averaging 6,690 g and 5,210 g respectively (Fleagle, 1999). Alouatta is a member of the Atelinae, a group of large-bodied arboreal platyrrhines that includes the spider monkeys, woolly monkeys, and woolly spider monkeys. Howlers range from Argentina all the way to southern Mexico and are more folivorous than other platyrrhines (Fleagle, 1999). Alouatta has a distinctive cranium with an elongated face and very deep mandible. Its hyoid bone, which sits below the mandible in the throat, is expanded into a balloon-like structure that acts as a resonating chamber for their namesake vocalizations (Fleagle, 1999).

This male specimen, the skull of a juvenile (M3 erupting), was collected in Rio Guaimaral, Colombia on the 30 August 1942 by P. Hershkovitz. 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

dorsal view

This specimen was scanned by Matthew Colbert on 10 June 2002 along the coronal axis for a total of 460 slices. Each slice is 0.2237 mm thick, with an interslice spacing of 0.2237 mm and a field of reconstruction of 99.0 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.

MacPhee, R. D. E. & 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.

Links
Alouatta seniculus on Animal Diversity Web (University of Michigan)

Alouatta seniculus on Primate Info Net (University of Wisconsin, Madison)

See more images of Alouatta seniculus from Last Refuge Ltd.

Face slice movie: