The developing renal, reproductive, and respiratory systems of the African elephant suggest an aquatic ancestry

^*Department of Zoology, University of Melbourne, Parkville, Victoria 3052, Australia; and ^‡Department of Perinatal Medicine, University of Melbourne, The Royal Women’s Hospital, Carlton, Victoria 3053, Australia

Communicated by Judith Kimble, University of Wisconsin, Madison, WI (received for review December 28, 1998)

Abstract

The early embryology of the elephant has never been studied before. We have obtained a rare series of African elephant (Loxodonta africana) embryos and fetuses ranging in weight from 0.04 to 18.5 g, estimated gestational ages 58–166 days (duration of gestation is ≈660 days). Nephrostomes, a feature of aquatic vertebrates, were found in the mesonephric kidneys at all stages of development whereas they have never been recorded in the mesonephric kidneys of other viviparous mammals. The trunk was well developed even in the earliest fetus. The testes were intra-abdominal, and there was no evidence of a gubernaculum, pampiniform plexus, processus vaginalis, or a scrotum, confirming that the elephant, like the dugong, is one of the few primary testicond mammals. The palaeontological evidence suggests that the elephant’s ancestors were aquatic, and recent immunological and molecular evidence shows an extremely close affinity between present-day elephants and the aquatic Sirenia (dugong and manatees). The evidence from our embryological study of the elephant also suggests that it evolved from an aquatic mammal.