Onthophagus nasutus Guerin-Meneville 1855

Onthophagus nasutus species group*. This group is diagnosed by a male having a clypeal horn (Fig. 5.1); female frons never with a horn (either unarmed or with simple straight carina); male protibia short and stout, with a broad brush of setae at the apex subequal in length to the apical spur (Figs. 1.16 –22); metatibial apex, with short thick setae, alternating with other thin and long setae three times or more the length of the thick setae (Fig. 5.4); female anterosuperior region of pronotum simple, never carinate. The species forming this group were initially considered part of the O. clypeatus species group by Boucomont (1932), Zunino & Halffter (1981, 1997), and Kohlmann & Solís (2001). Zunino & Halffter (1981), when first establishing the existence of the O. clypeatus species group, indicated that the species belonging to the O. nasutus species group might belong to another (unnamed) group. They considered the following species as part of this possible different group: O. carpophilus Pereira & Halftter, O. nasicornis Harold, O. nasutus Guérin-Méneville, O. sharpi Harold, O. tapirus Sharp, and O. rostratus Harold. Subsequently, Howden & Gill (1987) considered the existence of an O. nasicornis – O nasutus species complex within the O. clypeatus species group. Delgado & Deloya (1990) proposed an O. nasutus line, separate from an O. clypeatus and O. mirabilis species lines, all three lines forming part of an O. clypeatus species group. Although their taxonomic discussion is not clear, they proposed within this O. nasutus line, an O. nasutus species complex formed by: O. atriglabrus, O. nasicornis, O. nasutus, and O. villanuevai. Later, Zunino & Halffter (1997) maintained this O. nasutus species group as the O. nasicornis species complex, a part of the O. clypeatus species group. Subsequently, Delgado et al. (2006) excluded the O. nasicornis species complex from the O. clypeatus species group (sensu Zunino & Halffter 1997) based on the lack of tubercles and horns on the vertex of males without formally establishing a species group. Finally, Rossini & Génier (2024) established two subgroups, O. clypeatus and O. nasutus, as part of the O. clypeatus species group. Whereas Rossini & Génier (2024) give a complete list of the species belonging to their O. clypeatus subgroup, they did not specify any species for their O. nasutus subgroup. The mtDNA barcode and maximum-likelihood analyses recover this group. The barcode analysis (Figs. 1–2, 6) suggests a relationship with the O. hircus species group. Emlen et al. (2005: fig. 4) and Schwery & O'Meara (2021: fig. 1) also suggested this same relationship. In contrast, the bootstrap and partition analyses propose a relationship with the O. clypeatus – O. dicranius species groups with a low node support value of 9. Unlike most Western Hemispheric Onthophagus, this species group is not coprophagous but, instead, frugivorous, mycophagous, necrophilous, and saprophagous. The Emlen et al. (2005: fig. 4) phylogenetic tree showed that O. sharpi Harold (O. nasutus species group) falls within a branch composed of O. haematopus Harold and O. marginicollis Harold (both species members of the O. hircus species group) with bootstrap support of 88; therefore, supporting the results presented in Fig. 1 and Fig. 2, where O. hircus and O. nasutus appear as sister species groups. Emlen et al. (2005: fig. 6a) considered that O. sharpi gained a clypeal horn in an independent evolutionary process from the O. clypeatus species group. This species group is distributed from Mexico to Ecuador.