Date of this Version
Edmonds WD. 2023. Taxonomic review of the North American dung beetle genus Melanocanthon Halffter, 1958 (Coleoptera: Scarabaeidae: Scarabaeinae: Deltochilini). Insecta Mundi 1014: 1–28.
This paper presents a taxonomic review of the genus Melanocanthon Halffter, a group of ball-rolling (telocoprid) dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) endemic to eastern North America. The genus comprises five species, each keyed, diagnosed, illustrated and presented with information on distribution, relationships, and biology: Melanocanthon punctaticollis (Schaeffer), M. granulifer (Schmidt), M. nigricornis (Say), M. bispinatus (Robinson) and Melanocanthon vulturnus Edmonds, new species.
This paper is a sequel to the recent taxonomic study of Boreocanthon (Edmonds 2022). Melanocanthon and Boreocanthon are very closely related, distinct phylogenetic lineages with affinities to the pilularius species group of Canthon (Halffter 1961) and the monotypic taxon, Bajacanthon obliquus (Horn) (Halffter et al. 2022). The goal of this paper is a taxonomic review of the genus Melanocanthon and its constituent species. These two studies are contributions to the systematic background necessary for a future study of the historical biogeography of the native deltochiline fauna of the United States. Melanocanthon is virtually endemic to the United States, and Boreocanthon largely so. Remaining to complete the taxonomic picture is a re-examination and review of the pilularius species group of Canthon (sensu Halffter 1961), also mostly restricted to the United States.
Halffter (1958) created the genus Melanocanthon to accommodate four United States species of Canthon: C. nigricornis (Say, 1823), C. granulifer Schmidt, 1920, C. punctaticollis Schaeffer, 1915, and C. bispinatus Robinson, 1941. He designated Canthon bispinatus Robinson type species of the new genus. Among the features characteristic of the group, Halffter cited a) the presence of two apical spurs on the hind tibiae; b) a deeply V-shaped labio-gular fimbria; c) a spinate subclypeal process; and d) an otherwise very strong similarity to the genus Boreocanthon, which he created at the same time as Melanocanthon (Halffter 1958).
The first de-facto taxonomic study of Melanocanthon was that published by Robinson (1941) as a review of the “nigricornis [species] group of Canthon,” which he later incorporated into a broader study of Canthon inhabiting the United States (Robinson 1948). Halffter’s (1958) study essentially formalized Robinson’s view by creating the genus Melanocanthon to subsume the nigricornis species group. As considered here, the genus conserves the Robinson-Halffter taxon with the exception that Florida populations previously regarded as M. granulifer by Woodruff (1973) are here assigned to the new species, Melanocanthon vulturnus.
As observed by Edmonds (2022), cladistic studies that include Melanocanthon, as well as Boreocanthon, are very few. In those by Kohlmann and Halffter (1990) and Medina et al. (2003), the two resolved as sister groups; and, in that by Halffter et al. (2022), Boreocanthon (Melanocanthon was not considered) resolved as sister group to Bajacanthon, a monotypic group endemic to the southern tip of Baja California. Clearly much remains to be learned regarding the phylogenetic picture of these three groups, as well as the pilularius species group of Canthon, in the overall context of the history of the autochthonous deltochiline fauna of North America.