Relationships among the living squirrels of the Sciurinae. Bulletin of the AMNH ; v. 118, article 4

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New York : [American Museum of Natural History]
"Discovery of a character of the skull that appeared to sort some of the squirrels of the subfamily Sciurinae into the tribes into which they had previously been assignable only on the basis of genital characters resulted in a search for other skull characters for a testing of the existing sciurine classification. Three of the six subfamilies proposed by Pocock (1923) and scaled down to tribes by Simpson (1945), namely, the Xerini, the Tamiasciurini, and the Marmotini, are here shown to be distinguishable by skull characters. The tribes Sciurini and Callosciurini, which possess the most consistently distinctive characters of the baculum (os penis), are accepted as valid tribes on those characters alone. These last two are found to be constituted by three and two phyla, respectively, which are distinguished by characters of the skull and which are recognized as subtribes. The sixth tribe, the Funambulini, is shown by skull characters to consist of three distinct phyla. The tribe Funambulini as restricted is accepted, and two phyla are here raised to tribal rank, the Protoxerini and the Ratufini. Eleven phyla, six of them tribes and five the subtribes of the Sciurini and the Callosciurini, are defined and diagnosed by means of skull characters in considerable detail. Their possible relationships are discussed on the basis of such definitions and diagnoses and other available information. A key to the tribes and subtribes based on characters of the skull is offered, and many genera are for the first time given an adequate diagnosis on characters of the skull. A classification of the Sciurinae is offered which integrates as closely as possible the findings of the present study with what seems validated of earlier work. This consists of eight tribes, 11 subtribes, and 37 genera. Because the problem of whether or not the pygmy squirrels constitute a monophyletic unit had never been adequately treated, the skull character evidence for and against such a concept is here marshalled, considered, and concluded to be strongly against. The pygmy squirrel likenesses apparently represent convergence. An enumeration and comparison of the taxonomic skull characters of the genera of Sciurinae reveal indications of great conservatism in genera occupying the typical tree squirrel niche, and perhaps a basic ground squirrel niche and a long-nosed squirrel niche, whereas genera occupying other sciurine niches appear to have had greater freedom to acquire skull character specializations. The South American genus Sciurillus is thought to be too highly differentiated to have originated in South America, because an isthmus made that continent available to squirrels in the late Pliocene. It is suggested that it evolved in a tropical southern extremity of North America before an isthmus arose"--P. 201.
p. 157-206 : ill., maps ; 27 cm.
Includes bibliographical references (p. 205-206).