Say ‘No’ to Notoungulata. Turns out, it’s not a clade.

This is where testing takes us out on yet another limb
because the Notoungulata has been a clade for over 100 years (Roth 1903). If you are unfamiliar with this clade, as I was… you can get a basic education on the Notoungulata here,

According to
Darin Croft, PhD, Paleomammalogist, the Notoungulata is a clade of diverse South American Tertiary mammals all united, “by characters of their ear region and their teeth, including the presence of a loph on their upper molars known as the ‘crochet‘.” 

The clade Notoungulata produced taxa convergent with:

  1. buffalo/rhinos: Toxodon
  2. elephants/hippos: Pyrotherium. Astrapotherium
  3. chalicotheres: Homalodotherium
  4. peccarys: Thomashuxleya
  5. rabbits:  Protypotherium
  6. and others

Unifortunately
as I keep adding notoungulates to the large reptile tree (Fig. 1; 808 taxa at present), they keep nesting not with each other, but with a diverse selection of placental and marsupial mammals. That should not be happening, unless a false paradigm is present.

Figure 1. A selection of purported notoungulates (in amber) were added to the LRT and they did not nest together. That means they're not a clade.

Figure 1. A selection of purported notoungulates (in amber) were added to the LRT and they did not nest together. That means they’re not a clade.

Are dental characters
over-emphasized in traditional studies? including the Notoungulata? Do the cusps and valleys of molars trump the rest of the mammal’s morphology? Is it more reasonable to posit that teeth might be converging in these disparate taxa? For instance, Homalodotherium is an excellent sister to Chalicotherium, but I did not test the tooth cusps. And Toxodon is an excellent wombat. We’ll take closer looks at those taxa in future blogs.

Questioning basic assumptions is okay
because this is Science and everything is up for discussion. If a test does not deliver promised results, it’s okay to wonder why.

If we were to take the Notoungulata at face value
we would have to accept the wide range of morphologies within this one clade, as in the clade that includes tenrecs and whales. Unfortunately, testing shows that the range of body types in the Notoungulata is more readily matched by other clades, including the wombats within the marsupials and the chalicotheres within the placentals.

The loss of the clade ‘Notoungulata’
follows a list of other clades that have been lost based on the results of the LRT.

  1. Amniota is now a junior synonym for Reptilia
  2. Ornithodira is now a junior synonym for Reptilia
  3. Parareptilia is now a junior synonym for Reptilia
  4. Pterodactyloidea is paraphyletic
  5. Allotheria:  no mammals form a clade between Metatheria and Eutheria
  6. And others…

In counterpoint,
several new clades have been erected, resurrected or revised here:

  1. Archosauromorpha
  2. Lepidosauromorpha
  3. Enaliosauria = plesiosaurs + ichthyosaurs and their kin
  4. Tritosauria – a previously unrecognized squamate clade
  5. Prosquamata – another previously unrecognized squamate clade
  6. Fenestrasauria (goes back 16 years to Peters 2000, but still not used in academic publication
  7. Tenreccetacea = tenrecs + whales
  8. And several others…

Share your thoughts on this matter,
if you wish…

References
Billet G 2011. Phylogeny of the Notoungulata (Mammalia) based on cranial and dental characters. Journal of Systematic Palaeontology 9:481-497.
Cifelli RL 1993. The phylogeny of the native South American ungulates; pp. 195-216 in F. S. Szalay M J Novacek, and MC McKenna (eds.), Mammal Phylogeny: Placentals. Springer-Verlag, New York.
Roth S 1903. Los Ungulados Sudamericanos. Anales del Museo de La Plata (Sección Paleontológica). 5: 1–36. OCLC 14012855.
Scott WB 1932. Mammalia of the Santa Cruz Beds. Volume VII, Paleontology. Part III. Nature and origin of the Santa Cruz Fauna with additional notes on the Entelonychia and Astrapotheria. ; pp. 157-192 in W. B. Scott (ed.), Reports of the Princeton University Expeditions to Patagonia, 1896-1899. Princeton University, E. Schweizerbart’sche Verlagshandlung (E. Nägele), Stuttgart.

wiki/Notoungulata

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s