Key to Western Hemispheric Onthophagus species groups

We provide a preliminary identification key for the different species groups. Current diagnoses for the groups will require more species to stabilize the characters that define the aggregations. On the other hand, many morphological characters suggested by the COI groupings have not been customarily used for the Western Hemispheric Onthophagus systematics, like protibial and metafemoral shapes, protibial apical setae, protibial apical projections, apical metatibial setae, and the position of the horns.

The key is based mostly on males. There are no general invariant external morphological differences between both sexes, these can vary from species group to species group, we indicate here the more common ones. Males usually have the head horned or tuberculate and (or) the pronotum with horns or other protuberances; in many cases males have long and slender protibiae with a short apical spur and an apical brush or tuft of setae. Females have generally the head carinate and sometimes the pronotum with a carina or other minor elevation; in many cases females have short and thick protibiae with a long apical spur and never with an apical brush of setae.

Identification key to the Western Hemispheric Onthophagus species groups

1 Elytral intervals with a median row of tubercles each bearing a strong seta; pygidium with distinct umbilicate punctures, Cuba ......................................................................... O. marginatus species group

- Elytral intervals without median row of tubercles; pygidium without distinct umbilicate punctures..................... 2

2 Male protibia apex with a brush or tuft of long setae (Figs. 1.31 –38, 1.56–58, 1.67–90).............................. 3

- Male protibia apex with some short setae smaller or subequal to the length of the apical spur (Figs. 1.1 –15, 1.16–22, 1.23–30, 1.39–55, 1.59–66).................................................................................... 7

3 Males with clypeal horn (Figs. 5.1–3)..................................................................... 4

- Males without clypeal horn............................................................................. 4

4 Pronotum and elytral interstriae smooth with feeble punctures, with metallic luster (poorly defined in O. andersoni and O. grataehelenae); pygidium finely punctate............................................. O. clypeatus species group

- Pronotum and elytral interstriae rough with coarse punctures, without metallic luster; pygidium with large coarse punctures, giving the impression of looking like a honeycomb..................................... O. dicranius species group

5 Male with two curved horns at vertex (Fig. 5.6); dorsum with very long setae.................. O. crinitus species group

- Male with no head horns; dorsum with small setae or with long, erect setae at elytral apex and pygidium............... 6

6 Pronotum with four transversely aligned tubercles along a straight carina (Figs. 5.7–8); metafemur light brown with fine punctures (Figs. 2.57 –58); excavate posterior pronotal margin with a line of large, ocellate punctures (disappearing towards middle) and with one short, stiff, upward-pointing seta; apex of elytra and pygidium with long, erect setae............................................................................................. O. gazellinus species group

- Pronotum with a small central protuberance (Fig. 5.9 –10); metafemur brown to black with large punctures (Figs. 2.31 –38); excavate posterior pronotal margin impunctate, surface smooth; apex of elytra and pygidium glabrous or with or short setae................................................................................. O. landolti species group

7 Males with clypeal horn (Figs. 5.1); 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)....................................... O. nasutus species group

- Males without clypeal horn; metatibial apex, with short, thick setae of equal length (Fig. 5.5)......................... 8

8 Male pronotum with a plate-like horn (Figs. 5.11 –13)........................................................ 9

- Pronotum unarmed or with a small anteropronotal projection or gibbosity........................................ 11

9 Apical and internal male protibial margin projected like a round pointed spur (Figs. 1.23 –25, 1.39–43)................ 10

- Apical and internal male protibial margin projected like a thin pointed spur (Figs. 1.26 –28).... O. mexicanus species group

10 Male protibial spur bent downwards, strongly so in O. cynomisi (Figs. 1.39 –43)................. O. hecate species group

- Male protibial spur strongly bent inwards (Figs. 1.23 –25)................................. O. eulophus species group

11 Male pronotum with a small, pointed or rounded anteropronotal projection (Fig. 5.14); males without head horn......................................................................................... O. hoepfneri species group

- Male pronotum with no small conical central pronotal projection present; males with head horns (Figs. 5.15 –16), if head horn small, then pronotum with a large central gibbosity (Figs. 5.17 –18) ............................................. 12

12 Male pronotum with a large, central gibbosity and usually with well-marked, small lateral tubercles (Figs. 5.17 –18); well-developed males with small head horns (Figs. 5.17 –18).................................. O. chevrolati species group

- Male pronotum without large, central gibbosity and limited only between cephalic horns; males with well-developed head horns (Figs. 5.15 –16)................................................................................. 13

13 Disc of pronotum distinctly tuberculate; male protibial spur inwardly bent at apex (Figs. 1.29 –30); metafemur long and slender (Figs. 2.29 –30); apex of parameres well developed and defined; inhabitant of Neotoma nests..... O. velutinus species group

- Disc of pronotum without tubercles; male protibial spur downward bent at apex (Figs. 1.1 –15); metafemur short and stout (Figs. 2.1 –15); apex of parameres poorly developed; not an inhabitant of Neotoma nests.................................. 14

14 Apical and internal margins of male protibia with acuminate tooth and short protibia (Figs. 1.1–7)................................................................................................... O. curvicornis species group

- Apical and internal margins of male protibia obtuse with a short male protibia (Figs. 1.8 –15), or long protibia with apical and internal margin with acuminate tooth (O. confusus)........................................ O. hircus species group