The Orbital Mosaic in Prosimians and the Use of Variable Traits in Systematics

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Abstract
Study of 579 skulls, representing all 33 extant prosimian species and several anthropoids, shows that an orbital exposure of the ethmoid occurs in most Malagasy genera. A palatine-lacrimal contact is normal only in Lemur; the zygomatic-lacrimal contact occurs in most lorisiform species. Lepilemur shows possibly significant resemblances to lorisiforms. The vomer appears in the orbit of some ceboids. Cebids are distinguished by a canal running from the orbital apex through the basicranium. It is argued that skull shape and jaw musculature affect the size and shape of certain orbital-mosaic components. Frequencies of traits, rather than typologically ‘normal’ traits, may be taken as synapomorphies linking different species cladistically.