Temporal range: Late Eocene
The first discovery of Biretia was a single tooth at the Bir el Ater site. Aged at approximately 37 mya Original species found was Biretia piveteaui found in 1988. Recently however two new species have been classified, B. fayumensis and B. megalopsis both in 2005. Discovered in Birket Qarun Locality 2 (BQ-2) located about 60 mi south of Cairo in Egypt's Fayum depression. A very small anthropoid it only weighed around 280 to possibly 380 grams. Fragments from the jaw suggest it had had very large eyes in proportion to its body size which would suggest that it was nocturnal. "Biretia is unique among early anthropoids in exhibiting evidence for nocturnality, but derived dental features shared with younger parapithecids draw this genus, and possibly 45-million-year-old Algeripithecus (Strepsirrhini), into a morphologically and behaviorally diverse parapithecoid clade of great antiquity." 
The smallest of the species B. fayumensis had an estimated weight of 273 g, while the largest of Biretia, the B. megalopsis had a weight of about 376g. Adaptations of the skull of B. megalopsis are easily comparable to the modern tarsiers a small, modern Asian primate whose nocturnal insectivorous lifestyle. We infer this possibility of a nocturnal lifestyle from B. megalopsis' truncated molar root, which was so in order to made room for the large eye socket typical of a nocturnal primate. The large eye structure and similarity to the modern tarsiers also suggests that it has lost its tapetum lucidum. Thus, B. megalopsis demonstrates itself as being the oldest known nocturnal primate.
The genus is otherwise known only from a handful of fossil fragments, including a few maxilla fragments and some teeth and teeth fragments from the different species.
Fossil fragments The fossil fragments found for B. fayumensis, new species, include a composite of isolated P2 (DPC 21759C), P3(DPC 21249E), P4 (DPC 21371A), M1 (DPC 21250D), and M2 (DPC 21539E. For B. megalopsis, new species, maxilla with M1 through M3 (DPC 21358F).
||This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. (January 2012)|
- Rossie, James B., Ni,Xijun, and Beard, K. Christopher (2006) “Cranial remains of an Eocene tarsier” PNAS. 2009 Retrieved October 2009
- Gunnell Gregg F., Miller, Ellen R. (2001) “Origin of Anthropoidea: Dental Evidence and Recognition of Early Anthropoids in the Fossil Record, With Comments on the Asian Anthropoid Radiation” American Journal of Physical Anthropology Retrieved October 2009
- Rasmussen D. Tab, Simons Elwyn L. (1992) “Paleobiology of the Oligopithecines, the Earliest Known Anthropoid Primates” International Journal of Primatology, VoL 13, No. 5, 1992 Retrieved October 2009
- Simons Elwyn L, Seiffert Erik R., Chatrath Prithijit S., Attia Yousry (2001) “Earliest Record of a Parapithecid Anthropoid from the Jebel Qatrani Formation, Northern Egypt” Folia Primatol 2001;72:316–331 Retrieved October 2009
- Seiffert Erik R., Simons Elwyn L.,Clyde William C.,Rossie James B., Attia Yousry Bown Thomas M., Chatrath Prithijit, Mathison Mark E. “Basal Anthropoids from Egypt and the Antiquity of Africa's Higher Primate Radiation” Science 14 October 2005: Vol. 310. no. 5746, pp. 300–304 Retrieved October 2009