Expert: Dana Krempels, Ph.D. - 9/25/2007

Question
I have a question regarding the classification of mammals. The old view, based on morphology, grouped even- and odd-toed hoofed mammals together with elephants and their kin in a group called Ungulata. However, more recent studies have split up this grouping. The molecular evidence seems to indicate that the even- and odd-toed hoofed mammals are part of a new clade called Laurasiatheria, and elephants and their kin are part of a new clade called Afrotheria. Where do the South American hoofed mammals (a.k.a. Meridiungulata) fit in this new classification scheme? Are they thought to be within either Laurasiatheria or Afrotheria, or perhaps closely related to one of these clades? Obviously, since they are extinct, no genetic studies can be done to show where the South American hoofed mammals belong, but I'm wondering what the prevailing opinion is as to their relationship to other mammals.

Thanks,
David J. Cupo

Answer
Dear David,

What very little I know about these clades, I will share.  But this isn't my area of expertise.  :)

The prevailing hypothesis at the moment, as I understand it, is that the Meridiungulata arose from an ancestral Laurasiatherian that migrated down from North America.  

Some experts have suggested that the Meridiungulata may not be monophyletic, with some meridiungulates sharing a more recent common ancestor with the Gondwanian elephant clade (Embrithopoda) than with the Laurasian mammals.  But as you say, there's no nucleic acid around to put to the test.  Unless someone finds some frozen tissue, we may never know.

So I guess I'd say I'm not sure there *is* a prevailing opinion right now.  It's all relatively new, and still in the debate stages.  

Wish I could be of more help!

Take care,

Dana