The heterogeneity of the Family Fringillidae has been emphasized by many authors. The relationships of the species now included in this Family have been the subject of much discussion and constitute an important problem in avian systematics.
Sushkin's studies (1924, 1925) of features of the horny and bony palates have served as a basis for the present division of the Family into subfamilies. Recently, Beecher (1951a, 1951b, 1953) and Tordoff (1954) have used these features and others which they thought to be of value in an attempt to clarify the relationships of the species involved.
Beecher's work (1951a, 1951b, 1953) on jaw-musculature is a valuable contribution to our knowledge of the anatomy of passerine birds. His myological studies were so thorough and his presentation so detailed that students who disagree with his interpretations can draw their own conclusions. Beecher (1951b:276) points out that there are two basic types of skeletal muscle--those with parallel fibers and those with pinnately arranged fibers. The muscles with pinnate fibers seem to be more efficient, each muscle having a greater functional cross section for its bulk than does one with parallel fibers. He assumes that muscles with parallel fibers are more primitive, phylogenetically, than are those with fibers arranged pinnately. Since his study of the jaw muscles of the Icteridae (1951a) revealed that patterns of jaw-musculature within this Family remain constant regardless of the methods used in procuring food, he assumes that such patterns may be used as indicators of relationship throughout the entire oscinine group. These two assumptions, then, serve as the basis for his hypothesis concerning relationship and phylogeny within this assemblage. Beecher (1951b:278-280; 1953:310-312) maintains that within the Family Thraupidae there are two main lines which lead with almost no disjunction to the Carduelinae and Richmondeninae. The thraupid-richmondenine line involves a shift in the nature of the _m. adductor mandibulae externus superficialis_, which becomes more pinnate in the richmondenines. This results in greater crushing power. The thraupid-cardueline line involves a shift in emphasis from the the _m. adductor mandibulae externus medialis_ to the _m. pseudotemporalis superficialis_ and the forward advance of the insertion of the latter. This, also, promotes greater crushing ability. He states that features of the horny palate and of the plumage provide further evidence of close relationship of these groups. He includes, therefore, the Thraupinae, the Carduelinae, and the Pyrrhuloxiinae (=Richmondeninae) in the Family Thraupidae. Beecher (1953:307) indicates that the patterns of jaw-musculature of the Parulinae (wood warblers) and Emberizinae (buntings) are similar and suggests that the buntings had their origin from the wood warblers. He includes these subfamilies, therefore, in the Family Parulidae.