Distribution: from the north-central United States south to Argentina. Ten species are found exclusively in South America, and another ten species are found exclusively in North and Central America.  Seven species are shared between Central and South America.

Composition: 26 species (Endrödi 1985a; Dechambre and Lumaret 1985).

Diagnosis: species of Tomarus can be recognized by an attenuate clypeus that is bidentate and relatively narrow at the apex, mandibles usually visible from above and with two or three lateral teeth, frontoclypeal region with two tubercles or a transverse carina, and pronotum with or without an apical tubercle and subapical fovea.
Considerable reliance must be placed on the form of the male parameres for identification.  It should be noted, therefore, that the parameres are usually extremely fragile (almost parchment-like), and that they break or tear easily.  Great care should be taken when extracting the parameres from the abdomen.

Taxonomic history: both Tomarus Erichson and Ligyrus Burmeister were described in 1847.  Ever since the 1850s, Ligyrus has been used as the senior name by all authors, while Tomarus has been used as a subgenus.  The forward in Burmeister’s Handbuch der Entomologie (volume 5) is dated February 1847, and it was received in the library of the Entomologischen Vereine zu Stettin in September 1847.  However, a paper FOLLOWING Erichson’s in the Archiv für Naturgeschichte is dated January 1847 (before Burmeister’s book), and it was received in the library in Stettin in April 1847, five months before Burmeister’s book.  Therefore, the generic name Tomarus has priority, although Lacordaire stated in 1856, for reasons known only to him, that Tomarus was described after Ligyrus.  The confusion over the correct name for this genus seems to stem from this point, and all subsequent authors have incorrectly used Ligyrus.  Had the name Tomarus not been used as a valid name since 1899, there might have been a case for Reversal of Precedence (Article 23.9), but the name has been so used, notably by Endrodi (1969, 1985a).  The genus name Tomarus was raised from synonymy by Ratcliffe (2002b, 2003a).

Larvae: in general, larvae are found in soil rich in organic matter where they feed, sometimes on the roots of living plants.

Biological notes: life history information for most of the species is sparse.  Adults are nocturnal and attracted to lights. 

Literature cited:
Dechambre, R.-P. and J.-P. Lumaret. 1985. Un Ligyrus nouveau (Coleoptera, Dynastidae). Description de l’imago, de la larve et indications éthologiques. Revue Française d’Entomologie (N.S.) 7: 107-110.

Endrödi, S. 1985a. The Dynastinae of the World. Dr. W. Junk Publisher, Dordrecht. 800 pp., 46 plates.