Summary
The phylogenetic relationship between the members of the super-order Paenungulata, the manatees, elephants and hyraces were investigated using amino acid sequence analysis of the oc A crystallin of the eye lenses of these animals. The analysis confirms the monophyletic origin of the orders Hyracoidea, Sirenia and Proboscidea and places the edentates as the oldest offshoot from the main eutherian stem, followed by the Paenungulates as the next branch. The results suggest that the manatee may be closer to the hyrax than to the elephant due to the presence of 72-Leu in the hyrax and the manatee but not in the elephant. Morphological evidence would indicate a closer relationship between the elephant and the manatee which, if true, would require a back-substitution of 72 Leu → Val in the elephant oc A chain or two parallel substitutions 72 Val → Leu in the hyrax and manatee.