The dwarf and pygmy sperm whales are the only two extant species in the family Kogiidae, and as their name suggests they are small compared to their distant cousin the sperm whale. Like sperm whales, their mouth is on the underside of their body, but unlike sperm whales they have very few and very small teeth that are sharply pointed and curved. Like sperm whales, they are suction feeders and eat mostly squid.
Knowledge about these species has been slow to accumulate, and in fact, the existence of the two species only became widely accepted in 1966 (Handley 1966). Our interest in better understanding cetacean systematics led us to amass a database of mitochondrial DNA control region sequences, and analyses of these data revealed a possible third species. The evidence for a phylogenetic species is that within the dwarf sperm whale (Kogia sima), the specimens collected in the Atlantic and Indo-Pacific Ocean Basins are reciprocally monophyletic. The haplotypes unique to each ocean basin are dramatically different with many fixed differences in their sequence. The samples in our data base suggest that the distribution of the two phylogenetic species do not overlap, and thus we need additional evidence to determine whether the two groups fit the definition of a biological species. That is, we need evidence of reproductive isolation between the two dwarf sperm whale clades before a new species can be recognized.
Chivers, S. J., R. G. LeDuc, K. M. Robertson, N. B. Barros, and A. E. Dizon. 2005. Genetic variation of Kogia Spp. with preliminary evidence for two species of Kogia sima.Marine Mammal Science 21(4):619-634.
Handley, C. O. 1966. A synopsis of the genus Kogia (pygmy sperm whales). Pp 62-69 in Whales, Dolphins and Porpoises (Norris, K. S., ed). University of California Press, Los Angeles, California.