In the current circumscription inclusive of the thousands of species belonging to groups previously classified as independent families such as Pselaphidae, Scydmaenidae and Scaphidiidae, the Staphylinidae are the largest family in the whole animal kingdom (Grebennikov & Newton 2009). To some extent, this help explaining the prodigious productivity of some authors, each of which has been responsible for the descriptions of hundreds and even a few thousands of species of these beetles. Within this huge family, there is obviously scope for restricting one’s activity to a subfamily or a tribe, as in the case of Arnaldo Bordoni who in his very impressive series of publications on rove beetles, by now close to 300 titles, has mainly focussed on the Xantholinini.
This bulky monograph, 506 pages with 1807 illustrations, is not the first big volume produced by this author. Bordoni’s monograph of the Xantholinini of the Oriental Region (Bordoni 2002) encompasses 998 pages and the large articles on those of Australia (Bordoni 2005a), New Zealand (Bordoni 2005b) and New Guinea (Bordoni 2010) are 100, 114 and 383 pages long, respectively. Except for the Nearctic Region, extensively revised by Smetana (1982), and the Neotropical Region, for which a monographic account is badly needed, for all remaining biogeographic regions one half of the xantholinine genera have been introduced by Bordoni in his publications, e.g. 15 out of the 29 genera of the Afrotropical region and 23 out of the 46 Palaearctic ones. Of the 425 species treated in the new monograph, 273 are described in this work as new.
The great value of comprehensive monographs of speciesrich groups, even if limited to a continent rather than embracing the world fauna, is often underestimated. Their importance extends far beyond the domain of taxonomy, to which the contribution of these works is more obvious, by providing keys for species identification and a reassessment of affinities very often requiring the establishment of new genera (14 are proposed in Bordoni’s monograph to accommodate a number of newly described species but also a number of those already known but improperly allocated to different genera). Monographs are also important for their rich information content about the geographic distribution of species and supraspecific taxa. In the present case we find, quite surprisingly, that the Cape Region contributes very little to the overall high level of endemism of the African xantholinine fauna.
Less obvious, but not less important, large taxonomic monographs are also precious galleries (and often, as in this case, also richly illustrated atlases) of phenotypic diversity that should not be ignored by evolutionary biologists. For example, in several taxa of Afrotropical Xantholinini a virtually unstudied form of asymmetry has evolved, in which one elytron slightly overlaps the other along the sutural margin. Of much wider relevance is perhaps another feature, the apparent lack of coevolution between male and female copulatory structures, a condition that suggests uncommon forms of mating behaviour.
The author of this monograph deserves praise for this new impressive accomplishment, based on first-hand examination of type material of virtually all nominal taxa of Afrotropical Xantholinini described thus far, and of a huge amount of previously unidentified material preserved in many museums and private collections and often collected during famous scientific expeditions spanning between 1911 and 1996.
My only complaint is the often inaccurate editing: for example, some works cited in the text (e.g., Moore 1964, Naomi 1985) are not listed in the References, and some typos (e.g. species for specimens) show up here and there, but, as far as I could ascertain, none of these formal defects reduces the value and usefulness of this monograph.