New findings on the origin of C avia intermedia , one of the world's rarest mammals

C avia intermedia , a rare species of cavy found exclusively on M oleques do S ul I sland, B razil, differs from other cavies in genetic and morphological characteristics and has been regarded as phylogenetically closest to C avia magna . Here, I present morphological evidence for the likely origin of C avia intermedia from an ancestor shared with C avia magna : an external female genital organ similar in size and appearance to the male's penis. Masculinization of the female genitalia has been observed in C avia magna but does not occur in C avia aperea , which suggests a sister relationship between C avia magna and C avia intermedia .