Open Access

Streblopus Van Lansberge, 1874 has been one of the most mysterious dung beetle groups of the Neotropical fauna, having a rather peculiar morphology, very few known specimens in collections and a difficult placement among the scarabaeine lineages. In this work, based on the examination of a recently collected series of specimens and a synthesis of some scattered, but deeply valuable, information available in the literature, we readdress many of the questions posed by past authors. It is shown that Streblopus is a relict genus composed of two currently living species of widely disjunct distribution, namely S. opatroides Van Lansberge, 1874, from patches of Atlantic Forest in the Brazilian states of Bahia and Espírito Santo, and S. punctatus (Balthasar, 1938), known from a few localities across Sub-Andean humid forests in the Peruvian and Ecuadorian Amazon Forest. We redescribe both and present in detail the evidence pointing to their validity as two independent species; a discussion of their remarkable sexual dimorphism is also given. The biogeography of Streblopus in South America is addressed, and we conclude that the present disjunct distribution of the genus is a consequence of the retreat of the tropical forest corridors that once connected the Atlantic Forest to the Amazon Basin through the South American Dry Diagonal during several periods of the Neogene, particularly until the Middle Miocene. Finally, we propose an African origin for the genus based on its close phylogenetic relationship with a group of Old World taxa ‒ particularly Circellium Latreille, 1825 and Scarabaeini. Having diverged from those groups in the late Upper Cretaceous, we argue that the ancestor of Streblopus arrived in South America crossing the Atlantic Ocean by rafting. We present a synthesis of data from a wide variety of biological groups to support our ideas and contend that long-distance dispersal hypotheses should be taken more seriously by scarab beetle specialists.

Although extensively studied by different authors over the past 150 years, the taxonomy of Canthon Hoffmannsegg, 1817 and allied genera (which are here informally referred to as 'Canthon sensu lato') still remains problematic. With the aim of resolving some of the questions surrounding these taxa, the present work reviews the taxonomy of one of them, the genus Sylvicanthon Halffter & Martínez, 1977. As defined here, Sylvicanthon is distributed mainly throughout the vast areas of tropical rainforests in the Neotropical region and includes 15 species divided into two groups: the enkerlini group, with a single species, S. enkerlini (Martínez et al., 1964) comb. nov., and the candezei group, with five subgroups: the candezei subgroup, with S. candezei (Harold, 1869), S. genieri sp. nov. and S. foveiventris (Schmidt, 1920); the aequinoctialis subgroup, with S. aequinoctialis (Harold, 1868) comb. nov. and S. proseni (Martínez, 1949) stat. et comb. nov.; the bridarollii subgroup, with S. bridarollii (Martínez, 1949), S. seag sp. nov., S. edmondsi sp. nov. and S. attenboroughi sp. nov.; the furvus subgroup, with S. furvus (Schmidt, 1920), S. monnei sp. nov., S. mayri sp. nov. and S. obscurus (Schmidt, 1920); and the securus subgroup, with a single species, S. securus (Schmidt, 1920) comb. nov. Three species originally included in Sylvicanthon are here (re)transferred to Canthon: Canthon xanthopus Blanchard, 1846 and C. machadoi (Martínez & Pereira, 1967) comb. nov., as well as C. cobosi (Pereira & Martínez, 1960) stat. et comb. nov., which had been previously in synonymy under C. xanthopus. Descriptions, redescriptions, illustrations and comparative tables on the external morphology (including the genital capsule) of the genus and its species are presented, as well as a detailed discussion on their biogeography, comparative morphology, hypotheses on their phylogenetic relationships, data on natural history and a detailed historical revision of the classification of 'Canthon sensu lato'. Finally, we also discuss the socalled 'species problem' (i.e., the definition of the scientific term 'species') and its consequences to dung beetle taxonomy and favour the solution offered by the Biological Species Concept.