Chionodacryon, Burns, Kevin J., Unitt, Philip & Mason, Nicholas A., 2016

Burns, Kevin J., Unitt, Philip & Mason, Nicholas A., 2016, A genus-level classification of the family Thraupidae (Class Aves: Order Passeriformes), Zootaxa 4088 (3), pp. 329-354 : 341-342

23. Chionodacryon , new genus ( Fig. 4 )

Type species. Emberiza speculifera d'Orbigny & Lafresnaye, 1837 (currently recognized as Diuca speculifera ).

Included species. Monospecific, includes only Chionodacryon speculiferum . Because the name Chionodacryon is neuter in gender and Diuca is feminine, the ending of the adjectival specific epithet changes to agree, as does that of the subspecies D. s. magnirostris , which becomes C. s. magnirostre.

Diagnosis. This genus is diagnosed by the specific characters of Emberiza speculifera d'Orbigny & Lafresnaye, 1837.

Etymology. The name is formed from the Greek χιών (“snow”) and Greek δάκρυον (“teardrop”), alluding to the large white spot below the bird’s eye, one of the characters distinguishing Chionodacryon speculiferum from Diuca diuca . Its gender is neuter.

Comments. Burns et al. (2014) showed that the two species currently placed in Diuca are distantly related with D. diuca (Molina, 1782) in the Thraupinae and D. speculifera in the Diglossinae. The discovery that D. diuca and D. speculifera are not sister taxa leads to a nomenclatural conundrum. In introducing the generic name Diuca, Reichenbach (1850) illustrated the bill, head, tail, outer primaries, and foot but did not describe any characters as diagnostic, list any species, or designate a type species. Under Article 12.2.7 of the International Code of Zoological Nomenclature (ICZN 1999), generic names proposed in this way before 1931 may be available, and many of Reichenbach’s names introduced similarly in the same work, Avium Systema Naturale, have been used continuously since 1850. In 1851, Cabanis (p. 135) proposed the name Hedyglossa as a substitute for Diuca , listing Diuca as a synonym and listing diuca alone, not speculifera , as a component species. In 1855, Gray (p. 79) listed Hedyglossa as a synonym of Diuca instead and explicitly designated speculifera as type species of the latter.

The necessity of allocating diuca and speculifera to different genera reopens the question of the type species of Diuca because the species that is not the type may require a new genus. The issue is resolved by Article 67.2 of the International Code of Zoological Nomenclature (ICZN 1999), hereafter the Code. In the first explicit assignment of species to either of the relevant genera Diuca Reichenbach and Hedyglossa Cabanis, Cabanis (1851: 135) listed only one, Fringilla diuca Molina, 1782 , which applies to both generic names, irrespective of Cabanis’s treating Diuca as a synonym of Hedyglossa . Under Article 67.2.2 of the Code, Fringilla diuca thus becomes the only species eligible for fixation as the type for either of these generic names, effectively by monotypy (Article 69.3). Consequently, Gray’s (1855) subsequent designation of speculifera as type species of Diuca is irrelevant, and if speculifera is to be assigned to a monospecific genus, a new generic name is needed for it. Accordingly we provide Chionodacryon here.

Figures

FIGURE 4. Maximum clade credibility tree from the Bayesian analyses of Burns et al. (2014). Subfamily Diglossinae shown. Labeling and format as in Fig. 1.