A Molecular Classification for the Living Orders of Placental Mammals and the Phylogenetic Placement of Primates
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For more than a century, systematists have debated higher-level relationships among the orders of placental mammals. The order Primates is noexception. One prominent hypothesis is Archonta that was originally proposed as a superorder by Gregory (1910) to include primates, bats, flying lemurs, and menotyphlan insectivores (i.e., tree shrews, elephant shrews). Minus elephant shrews, the Archonta hypothesis has survived for nearly a century. The bulk of support for this hypothesis derives from modifications of the tarsus (Novacek and Wyss, 1986; Shoshani and McKenna, 1998; Szalay, 1977; Szalay and Drawhorn, 1980; Szalay and Lucas, 1993). Archonta is a recurrent theme in higher-level mammalian classifications (McKenna, 1975; McKenna and Bell, 1997; Szalay, 1977). There are also morphological studies (Cartmill and MacPhee, 1980; Luckett, 1980; Novacek, 1980; Simpson, 1945) that question the monophyly of Archonta. Simpson (1945) suggested that Archonta is "almost surely an unnatural group." Even among studies that advocate Archonta, the possibility that bats are an independently arboreal group from the Archonta has been noted (Szalay and Drawhorn, 1980). In part, this reservation was expressed because bats lack shared, derived tarsal specializations that unite other archontans (Szalay, 1977; Szalay and Drawhorn, 1980). Szalay and Drawhorn (1980) attribute this to the major functional transformation that the chiropteran ankle has undergone in association with the "extreme reorientation of the femoral-acetabular articulation." Given the absence of tarsal modifications that unite bats with other archontans, the primary rationale for including bats in Archonta is the suite of novel features that bats share with flying lemurs (Gregory, 1910; Simmons, 1995; Simmons and Quinn, 1994; Szalay and Drawhorn, 1980). Aside from whether or not primates belong to a monophyletic Archonta, there are questions pertaining to the sister-group of primates. Several studies resolve archontans into a trichotomy between primates, tree shrews, and Volitantia (i.e., flying lemurs bats) (Novacek, 1990; Novacek et al., 1988; Novacek and Wyss, 1986; Szalay, 1977). Other studies, some of which support Archonta and others of which do not, support a sister-group relationship between primates (or euprimates) and tree shrews (Martin, 1990; Shoshani and McKenna, 1998; Simpson, 1945; Wible and Covert, 1987; Wible and Novacek, 1988). Beard (1993) has argued for the Primatomorpha hypothesis that postulates a sister-group relationship between flying lemurs and primates. Another alternative is a sister-group relationship between tree shrews and flying lemurs, with this collective group as the sister-group to primates (Sargis, 2001). Springer Science+Business Media, LLC 2007.