Two subspecies of the Greater bushbaby, Galago crassicaudatus argentatus and G. c. crassicaudatus, are known to differ morphologically, but quantitative studies of the differences, or of reproductive compatability between the subspecies, have not previously been attempted. Somatic measurements were made on living specimens of both subspecies and controlled experiments were conducted to determine whether fertile matings would occur between them.
G. c. argentatus is heavier than G. c. crassicaudatus and has longer ears, a longer ulna and fibula and a greater biorbital breadth. A significant degree of sexual dimorphism in body weight and length of the fibula and ulna occurs in G. c. argentatus, males being larger than females. In G. c. crassicaudatus however, there are no statistical differences between the sexes in these somatic measurements. The morphology of the male and female external genitalia differs between the two subspecies.
In six pairs of male argentatus and female crassicaudatus, only one pair mated and no offspring resulted. In seven pairs of female argentatus and male crassicaudatus, matings occurred in all pairs but only one female conceived and this pregnancy ended prematurely in a spontaneous abortion. In control experiments using six oppositely-sexed pairs of G. c. crassicaudatus, however, all females became pregnant and produced live offspring.
The morphological and reproductive differences between G. c. argentatus and G. c. crassicaudatus are more pronounced than previously realized and it is possible that the two varieties may merit separation as distinct species of Galago.