Canthon xanthopus Blanchard, 1846

Cupello, Mario & Vaz-De, Fernando Z., 2018, A monographic revision of the Neotropical dung beetle genus Sylvicanthon Halffter & Martínez, 1977 (Coleoptera: Scarabaeidae: Scarabaeinae: Deltochilini), including a reappraisal of the taxonomic history of ‘ Canthon sensu lato’, European Journal of Taxonomy 467, pp. 1-205 : 166-168

Canthon xanthopus Blanchard, 1846 restauration of original combination

Figs 7C , 45

Canthon xanthopum Blanchard, 1846: 166 .

Canthon xanthopum – Blackwelder 1944: 202.

Canthon xanthopus – Lacordaire 1856: 78. — Harold 1868a: 140, 144; 1869b: 995. — Gillet 1911: 34. — Schmidt 1922: 72, 82. — Balthasar 1939: 226. — Martínez 1949b: 188; 1959: 45–46. — Vulcano & Pereira 1964: 636. — Halffter & Martínez 1977: 63. — Krajcik 2012: 64.

Glaphyrocanthon xanthopus – Martínez et al. 1964: 8.

Sylvicanthon xanthopus – Halffter & Martínez 1977: 63.

Etymology

From the Greek word ‘ xanthos ’, meaning ‘yellow’. Referring to the leg’s yellowish colouration of this species, “ Canthon à pattes jaunes ” ( Blanchard 1846).

Material examined

Lectotype (here designated)

BOLIVIA: ♂, Santa Cruz, Vallegrande, cited by Blanchard (1846) as “ Province de Valle Graude ”, (“ LECTOTYPE ♂ / Canthon / xanthopum / Blanch. / des. F. Z. Vaz-de-Mello, 20 14 ”, “Type”, “ Canthon / xanthopus / Blanch ”, “Museum Paris / Santa-Cruz / (Valle Grande) / d’Orbigny 1834”, “ 6 B11 / 94 ”) ( MNHN) ( Fig. 45A ).

Additional material (7 ♂♂, 12 ♀♀)

BOLIVIA: Santa Cruz: 1 ♀, Samaipata, Refugio Los Volcanes, 18º06.3′ S, 63º35.9′ W, 1050 m, 21– 25 Feb. 2010, carrion, Edmonds and Vidaurre leg. ( TAMU); 7 ♂♂, 11 ♀♀, Samaipata, Refugio Los Volcanes, 18º06.3′ S, 63º35.9′ W, 1050 m, 21–25 Feb. 2010, dead millipede, Edmonds and Vidaurre leg. ( TAMU).

Collecting sites

BOLIVIA. Santa Cruz: Samaipata (Refugio Los Volcanes), Vallegrande.

Comments

The internal classification of the genus Canthon , as mentioned before, is extremely confusing and the genus is likely polyphyletic. Therefore, pointing out a clear relationship of C. xanthopus with any of the Canthon species groups could only be done in a tentative manner. By its overall morphology, especially regarding the shape of protibiae and the presence of a long humeral carina reaching the apex of elytra, C. xanthopus seems to be close to the four species of the maldonadoi group, which is part of the septemmaculatus lineage as defined by Halffter & Martínez (1977). Nonetheless, the presence of a carina separating pygidium from propygidium in C. xanthopus is a feature that distinguishes this species from the members of that group – which do not possess any separation between pygidium and propygidium – and places C. xanthopus in the nominotypical subgenus. Therefore, a more careful analysis of the members of Canthon should be performed before a more confident decision is taken on the relationship between C. xanthopus and any particular species group. Hence, this species is put in incertae sedis within Canthon s. str.

As discussed earlier in this work, the name Glaphyrocanthon cobosi was considered a junior subjective synonym of C. xanthopus by Halffter & Martínez (1977) and has remained so up until now. It is interesting to revisit the taxonomic history of both names to understand the historical context that ultimately led Halftter & Martínez to propose that synonymy.

The true identity of Canthon xanthopus , described from “Province de Valle Graude”, Santa Cruz, Bolivia, was a mystery to scarabaeidologists for more than a century since its description by Blanchard (1846), which was based on very vague and imprecize characters such as the shape of the clypeus and the colouration of the tegument. In his revision of Canthon, Harold (1868b) included C. xanthopus in a list of 23 species names he could not relate to any known species taxa, and that situation persisted even after his following year’s study of the MNHN collection ( Harold 1869c), where until today one of the syntypes of C. xanthopus is housed. The same is true for the revisions of Schmidt (1922) and Balthasar (1939), who did not include C. xanthopus in their identification keys.

The name, then, would not be mentioned again until Martínez et al. (1964). Those authors, in a footnote to their identification key to the species of Glaphyrocanthon , wrote that, judging only from its original description, it could be presumed that C. xanthopus was “very close” to Glaphyrocanthon cobosi Pereira & Martínez, 1960 , a species also described from Santa Cruz, Bolivia. Nevertheless, C. xanthopus was not included in their key because they claimed they had never seen specimens of this species in person. Thirteen years later, Halffter & Martínez (1977) stated they had finally found “the type ” of C. xanthopus in the MNHN. On examining it, they concluded that C. xanthopus and G. cobosi were synonyms and the species had to be transferred to Sylvicanthon .

During the preparation of this work, we found a specimen in the MNHN collected in 1834 by the French explorer and naturalist Alcide d’Orbigny (1802–1857) in the province of Vallegrande, Santa Cruz, Bolivia. That specimen fully agrees with Blanchard’s description and collecting data, which led us to consider it one of the syntypes of C. xanthopus , the only one known to us. No specimens found at the MNHN bear any label by Gonzalo Halffter or Antonio Martínez; therefore, we do not know which specimen they were referring to when they wrote they had examined “the type” of C. xanthopus .

The study of that syntype (now lectotype) of C. xanthopus ( Fig. 45A ) and its comparison with the holotype of G. cobosi ( Fig. 46A , deposited in the MACN) leave no doubt that the synonymy proposed by Halffter & Martínez (1977) is incorrect. Both species are easily distinguishable from one another by the shape of the eyes (with about 1/8 of the width of the interocular space in what is now known as Canthon cobosi , and 1/10, in C. xanthopus ), the shape of the protibiae (with tiny teeth and truncate apex in C. cobosi , and with large teeth and an apex occupied by the apical tooth in C. xanthopus ), the shape of the clypeal teeth (small, obtuse and separated from one another by a clypeal emargination in C. cobosi , and large, acute, without emargination in C. xanthopus ), and the hypomeron (strongly excavated, with a tooth on the external edge, with a complete hipomeral carina in C. cobosi , only slightly depressed, without any teeth, and with a very short hipomeral carina in C. xanthopus ). For a discussion on the transfer of both species to the genus Canthon , see the section ‘Species composition’ under Sylvicanthon above.

Figures

Fig. 7. Pterothorax, ventrolateral views. A. Sylvicanthon aequinoctialis (Harold, 1868) comb. nov. B. S. obscurus (Schmidt, 1920). C. Canthon xanthopus Blanchard, 1846. Abbreviations: MsC = mesocoxa; MMsC = external margin of mesocoxa; CMtE = centre of metaventrite; LMtE = lateral region of metaventrite; MtC = metacoxa.

Fig. 45. Canthon xanthopus Blanchard, 1846. A. Lectotype and its labels. B. An ordinary specimen.

Fig. 46. A. Canthon cobosi (Pereira & Martínez, 1960) stat. et comb. nov., holotype. B–C. Canthon machadoi (Martínez & Pereira, 1967) comb. nov. B. Paratype 2. C. Paratype 4.