Primates and their supraordinal relationships

Although primate origins and supraordinal relationships are discussed twice in Volume 2 (Chapter 1 on morphological and Chapter 2 on molecular data), I would like to mention some studies that have used ontogenetic data in this context. According to Hofer, one of the ultimate goals of primatology (Spatz 1964) is the elucidation of the phylogenetic position of primates compared to other mammals. Gregory (1910) formulated the concept of the Archonta, which unites Chiroptera (bats), Dermoptera (colugos), Menotyphla (Macroscelidea = elephant shrews and Scandentia = tree shrews), and Primates into one single superorder. Later on, modified versions of this hypothesis excluded the Macroscelidea (Novacek and Wyss 1986), while Adkins and Honeycutt (1993)

surprisingly favored a revival of this grouping based on molecular data (COII gene). Even after the Hennigian revolution (1950), many morphologists confirmed the traditional version of primate supraordinal relationships by defining synapomorphies (Hooker 2001). Noncladists, such as Szalay (Szalay and Drawhorn 1980; Szalay and Lucas 1993), supported the evolution and diversification of archontans in an arboreal milieu. The approach is based on the aim of "Darwinian evolutionary classification'' to include both adaptive similarity and monophyly sensu Bock and von Wahlert (1965). Critical comments can be found in Grande and Rieppel (1994).

Murphy et al. (2001), however, proposed the new superorder "Euarchonto-glires,'' based on nuclear and mitochondrial gene sequences of 42 placental specimens. This new grouping (Asher et al. 2005; Nishihara et al. 2006) consists of the Euarchonta (=Dermoptera + Primates + Scandentia) and the Glires (=Lagomor-pha + Rodentia). Surprisingly, bats are excluded and do not seem to be closely related to primates. MacPhee (1993 p 372) already noted (based on Adkins and Honeycutt 1993) that "... something is pulling the rodents toward the primates in this data set ''

These radical changes in primate supraordinal relationships consequently deny the Volitantia hypothesis (Illiger 1811), which favors a sister group relationship of bats and colugos (Leche 1886; Thewissen and Babcock 1991; but see Beard 1993). Wible and Martin (1993) documented that the ontogeny of the tympanic floor and roof does not provide any characters distinguishing all extant archontans from other eutherians. Actually, Archonta (archontans were supreme public servants of the Greek ancient world) has Scala naturae written all over it and represents a vehicle to explain the existence of flying mammals (Chiroptera) via a gliding intermediate stage (Dermoptera) in the absence of appropriate fossils (see also Sears et al. 2006). It should be emphasized that the concept of Scala naturae was long developed before the theory of natural selection (Martin 1973). Darwin (1859) promoted the view that nature does not make leaps— Natura non facit saltum—in order (1) to fill the gaps in the fossil record and (2) to strengthen his intellectual position (Schwartz 2000). Although Darwin's motives are plausible, accepting the Volitantia concept might be an immediate consequence of the emerging battle against supporters of divine creation. Rasmussen (2002 p 7) specified in a more diplomatic manner: "However, it is fair to say that at this juncture we do really not know if primates are more closely related to Scandentia, Plesiadapiformes, Chiroptera or Dermoptera. These four orders are conveniently lumped together as 'archontan' in what may be a true clade but which for lack of unambiguous evidence is often used as an informal grouping.'' Faute de mieux: chimeric archontans? In the context of primate evolution, some important examples of cranial and postcranial anatomy are presented here.

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