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South American octodontid rodents of the subfamily Octodontinae currently show low species richness but great morphological and chromosomal diversity. This diversity is interpreted alternatively as the remnant of a wider past radiation or as the result of saltational evolution. These hypotheses are discussed in relation to a phylogenetic analysis of the Late Pliocene octodontineAbalosia castellanosi. My results suggest thatAbalosia, together withTympanoctomys andOctomys, is part of a clade of desert specialist propalinal octodontids, which would have differentiated east of the Andes in the emergent semi-deserts of western Argentina. The presence ofAbalosia in the coastal region of central Argentina during the Upper Marplatan Age (Late Pliocene) suggests a pulse of expansion of such arid environments, probably coeval with the global climatic deterioration detected around the transition Gauss-Matuyama magnetic ages. The phylogenetic position ofA. castellanosi suggests that extinction events affected the clade of the octodontine desert specialists. Accordingly, regardless of how rough or gradual the differentiation of the octodontine’s diversity has been, the living representatives seem to be remnants of a wider radiation.

A morphometric study of the sperm ofCtenomys maulinus Philippi 1872 was carried out. A process of the postacrosomic region that probably correponds to a permanent structure in the sperms of these rodents, and is characteristic of the genus, was observed.

In the coastal region of central Chile the coruro, Spalacopus cyanus, lives in large populations consisting of many small, nomadic colonies. One colony contained 15 members belonging to no less than three generations. A colony of coruros occupies a common burrow system and apparently wanders continuously in search of food. Coruros feed primarily, if not exclusively, on the tubers and underground stems of the lily, Leucoryne ixiodes. S. cyanus has a higher metabolic rate than similar-sized fossorial species of Ctenomys. In February, adult males were sexually active and two of six adult females were pregnant, each bearing three small fetuses.

Allusions appear frequently in the literature to the idea that a special relationship exists between the African hystricomorph rodents Petromys and Thry-onomys and the Octodontidae and Myocastoridae (Capromyidae auct .), respectively, of South America. I have elsewhere ( In press ) reviewed the history of this arrangement and attempted to show that few positive reasons for classifying these two genera with South American families have ever been advanced. The idea derives ultimately from the unsupported assertion of Waterhouse (1839). Ellerman (1940) classified both Petromys and Thryonomys as sole representatives of the subfamilies Petromurinae and Thryonomyinae of the Echimyidae. This “Echimyidae” is roughly the equivalent of Simpson's (1945) “Octodontoidea,” so these two authors really classified Petromys and Thryonomys in the same way, as Simpson lists them under Petromyidae and Thryonomyidae of the Octodontoidea, stating (p. 212), “… Thryonomys and Petromys are morphologically octodontoid and it has been common practice to refer them to neotropical families and subfamilies, for instance, placing Petromys with Octodon and Thryonomys with Capromys .” Wood (1955) separates Thryonomys and Petromys from the South American hystricomorphs in his splitting apart of the suborder Hystricomorpha. He divides the hystricomorphs into two suborders: Hystricomorpha (Old World forms) and Caviomorpha (New World forms). He still asserts, however, that there is “morphological similarity” between Petromys and Thryonomys and New World families. He says (p. 184), “There are many obvious similarities to the Octodontidae and Echimyidae respectively. These are so great that formerly the African genera were placed in South American families. This is still done sometimes, the latest example being Ellerman, Morrison-Scott and Hayman (1953: 237–239) who consider the Thryonomyinae, Petromurinae and Echi-myinae to be subfamilies of the Octodontidae.” As a matter of fact, Ellerman, Morrison-Scott and Hayman (1953) concede that there may be some doubt about the classification of Thryonomys , …