Cranial morphology of Aegyptopithecus and Tarsius and the question of the tarsier‐anthropoidean clade

Abstract

New crania of the Oligocene anthropoidean Aegyptopithecus provide a test of the hypothesized tarsier-anthropoidean clade. Three cranial characters shared by Tarsius and some modern anthropoideans (apical interorbital septum, postorbital septum, "perbullar" carotid pathway) were examined. 1) An apical interorbital septum is absent in Aegyptopithecus. A septum does occur in Galago senegalensis (Lorisidae) and Microcebus murinus (Cheirogaleidae), so the presence of a septum is not strong evidence favoring a tarsiiform-anthropoidean clade. 2) In Aegyptopithecus and other anthropoideans, the postorbital septum is formed mainly by a periorbital flange of the zygomatic that extends medially from the lateral orbital margin onto or near the braincase. The postorbital plate of Tarsius is formed by frontal and alisphenoid flanges that extend laterally from the braincase to the zygomatic's frontal process, which is not broader than the postorbital bars of other prosimians. Periorbital flanges evolved in Tarsius for support or protection of the enormous eyes, as suggested by the occurrence of maxillary and frontal flanges that cup portions of the eye but do not separate it from temporal muscles. 3) The internal carotid artery of Aegyptopithecus enters the bulla posteriorly and crosses the anteroventral part of the promontorium. The tympanic cavity was probably separated from the anteromedial cavity by a septum stretching from the carotid channel to the ventrolateral bullar wall. In Tarsius, the carotid pathway is prepromontorial, and a septum stretches from the carotid channel to the posteromedial bullar wall. Quantitative analyses indicate that anterior carotid position has evolved because of erect head posture. The cranium of Oligocene anthropoideans thus provides no support for the hypothesized tarsier-anthropoidean clade.

New perspectives on anthropoid origins

“…Although most researchers have argued for homology between anthropoid and tarsier septa, others have argued that the tarsier septum represents a convergent adaptation necessitated by the evolution of extremely large eyes (82,83). Owls are similar to tarsiers in having postorbital processes that are less extensive than anthropoid septa, in having roddominated retinal foveae (lost in tytonid owls), and in being predominantly nocturnal (81).…”

Preliminary description of the cranium of Proteopithecus sylviae , an Egyptian late Eocene anthropoidean primate

“…3) and occupied a position similar to that seen in Saimiri or Callithrix. As has been pointed out (17), the position of the posterior carotid foramen is directly linked to the location of the midline anterior rim of the foramen magnum and usually lies about 1.5 mm anterior to it. Near the shattered occipital condyles and the foramen magnum the posterior lacerate and jugal foramina can be seen; however, much of the rest of the posterior basicranium in CGM 42214 and DPC 14095 are damaged or dislocated to the point that interpretation is unreliable.…”

Skull of the Eocene primate Omomys carteri from western North America

“…This intraorbital septum is not found in Omomys, but it has been found in small anthropoids and has been inferred to be present ancestrally in anthropoids (Ross, 1994). Skulls of the earliest fossil anthropoids have contradicted this hypothesis, however, since they lack this derived feature (Simons & Rasmussen, 1989;Simons, 1995). In small, large-eyed primates such as tarsiers, lorises, and mouse lemurs, the enlarged orbital wall incorporates a significant portion of the ethmoid plate rostrally, such that it borders the lacrimal bone (Simons & Russell, 1960).…”

“…Considerable research has been undertaken to document the presence, absence, and position of these branches in primates (Gregory, 1920;Klaauw, 1931;Saban, 1963;Russell, 1964;McKenna, 1966;Bugge, 1972;Szalay & Katz, 1973;Cartmill, 1975;Archibald, 1997;MacPhee, 1981;Wible, 1983Wible, , 1984Wible, , 1993MacPhee & Cartmill, 1986;Simons & Rasmussen, 1989;Ross, 1994;Beard & MacPhee, 1994;Norris & Harrison, 1998;Ross & Covert, 2000;Bloch & Silcox, 2001;Silcox, 2003). Bony canals or grooves trace the pathways of these arterial branches along the surface of the promontorium.…”