Order Artiodactyla Author Wilson, Don E. Author Reeder, DeeAnn text 2005 The Johns Hopkins University Press Baltimore Mammal Species of the World: a Taxonomic and Geographic Reference (3 rd Edition), Volume 1 637 722 book chapter 0-8018-8221-4 10.5281/zenodo.7316519 Okapia Lankester 1901 Okapia Lankester 1901 , Nature, 64: 24 . Type Species: Equus johnstoni P. L. Sclater 1901 Species and subspecies: 1 species: Species Okapia johnstoni P. L. Sclater 1901