Character evolution in the orbital region of the Afrotheria


Philip G. Cox, University Museum of Zoology, Downing Street, Cambridge CB2 3EJ, UK.


The orbit or eye socket is a highly plastic area of the mammalian skull. There is significant variation within and between the different mammalian orders in the size and position of the bones and foramina that contribute to this region. For this reason, orbital characters are often used in attempts to determine the relationships of the various mammalian groups. This study describes the orbital region of the Afrotheria, the proposed group of endemic African mammals that comprises the paenungulates (elephants, manatees and dugongs, and hyraxes), elephant-shrews, aardvarks, golden moles and tenrecs. Evolution within the Afrotherian orbit is then explored by scoring 19 orbital characters in each Afrotherian genus, and plotting the character state changes on to previously existing phylogenies of the Afrotheria. These phylogenies were all produced from recent molecular work. It was found that there is a great deal of variation in the orbital region within the Afrotheria, most notably in the size of the lacrimal and its contacts with other bones, the appearance of the palatine in the orbit and the structure of the zygomatic arch. Overall, orbital characters strongly supported an elephant-hyrax clade over the more traditional grouping of elephants and sirenians (Tethytheria) within the paenungulates. There was also support for a monophyletic Tenrecoidea (a clade of tenrecs plus golden moles). Additionally, it was shown that there is a great deal of variation in the orbital region among the genera of the Tenrecidae and the Macroscelididae.