Oryzomys megacephalus (G. Fischer 1814)

Wilson, Don E. & Reeder, DeeAnn, 2005, Order Rodentia - Family Cricetidae, Mammal Species of the World: a Taxonomic and Geographic Reference (3 rd Edition), Volume 2, Baltimore: The Johns Hopkins University Press, pp. 955-1189 : 1151

Oryzomys megacephalus (G. Fischer 1814)

[Oryzomys] megacephalus (G. Fischer 1814) , Zoognosia Tabulis Synopticis Illustrata: 71.

Type Locality: Paraguay, Canendiyu Dept., east of Río Paraguay, 13.3 km (by road) N Curuguaty, 255 m; 24º31′S, 55º42′W (as fixed by neotype designation by Musser et al., 1998:252).

Vernacular Names: Azara's Broad-headed Oryzomys.

Synonyms: Oryzomys capito ( Olfers 1818) ; Oryzomys cephalotes (Desmarest 1819) ; Oryzomys goeldi Thomas 1897 ; Oryzomys modestus J. A. Allen 1899 ; Oryzomys velutinus J. A. Allen and Chapman 1893 .

Distribution: Lowland tropical rainforests of E Amazonia—E and S Venezuela, Guianas, N and C Brazil, E Paraguay; including Trinidad; western limits indeterminate.

Conservation: IUCN – Lower Risk (lc).

Discussion: Oryzomys megacephalus (Fischer, 1814) is the oldest available name based on Azara’s (1801) "Rat second, ou Rat a grosse tete," a form conventionally known as O. capito ( Olfers, 1818) in the middle 1900s (e.g., Cabrera, 1961; Hall, 1981; Hershkovitz, 1960). Taxonomic understanding of this species was obscured by the infelicitous footnote of Hershkovitz (1960:544), who suggested the synonymy of some 20 taxa under O. capito , a passing opinion formally expanded by Cabrera (1961) and followed by other authors (e.g., Hall, 1981; Handley, 1966 a, 1976). The extremeness of this viewpoint was exposed by the karyotypic study of Gardner and Patton (1976), a watershed paper that has sparked critical review, still on-going, of this diverse species complex.

As a result, the following forms considered synonyms by Hershkovitz (1960) and/or Cabrera (1961) are now acknowledged as distinct species or as synonyms of other species (see separate accounts): O. bolivaris , boliviae (= O. nitidus ), castaneus (= O. bolivaris ), O. caracolus , intermedius (= O. russatus ), O. laticeps , O. legatus , magdalenae (= O. talamancae ), O. macconnelli , medius (= O. talamancae ), mollipilosus (= O. talamancae ), O. nitidus , oniscus (= O. laticeps ), O. perenensis , rivularis (= O. bolivaris ), sylvaticus (= O. talamancae ), O. talamancae , and O. yunganus . Nomenclatural priority, neotype designation, synonyms, and morphological definition of O. megacephalus proper addressed by Musser et al. (1998); phylogeographic relationships and other morphometric comparisons supplied by Patton et al. (2000); banded chromosomal comparisons with related species presented by Volobouev and Aniskin (2000). Sister species to O. laticeps ( Bonvicino and Martins Moreira, 2001; Costa, 2003) or the O. laticeps and O. perenensis clade ( Patton et al., 2000) based on cytochrome b sequence data .