Eutheria: Systematics, Part 2
The Mesaxonia, as defined here, include the horses, rhinos, elephants, and dugongs, among others. The group shares a number of foot, skull, and tooth characteristics which support its monophyly. However, no official name has been published for this group, and so we have borrowed the term Mesaxonia, which is still used by some authors to refer to the Perissodactyla.
The Hyracoidea, which is here placed with the elephants and dungongs, has been suggested to be closer to the Perissodactyls, based on a number of unusual morphological characters. This question has not been resolved.
The remaining groups (Proboscidea through Sirenia) are often referred to as the Tethytheres.