SVP abstracts 2017 – Notoungulata reexamined

Remember when
members of the clade Notoungulata were dismantled and shipped to various other clades within Theria in the large reptile tree (LRT, 1051 taxa)? Keep that in mind as you read this abstract by West 2017.

From the West 2017 abstract:
“Notoungulata is an extremely diverse and disparate, entirely extinct order of placental
mammals, largely endemic to South America, which persisted through Cenozoic. There
are disagreements on intraordinal relationships among notoungulates, but the roots of the
order within Placentalia are even more enigmatic. A critical challenge is the lack of DNA
(though one taxon now has yielded collagen protein sequences), thus the greater impact
of the interpretation of morphological homology across superorders, particularly for
herbivorous ungulate placentals. This is because most characters used in higher-level
analyses of Placentalia do not adequately capture the nuances of unguligrady,
cursoriality, lophodonty, and hypsodonty, hindering accurate phylogenetic
reconstructions.

“A long-held, recently reinforced, morphology-based hypothesis for Notoungulata is that
they are most closely related to Tethytheria, an afrothere group including elephants and
manatees. An alternative hypothesis, recently corroborated by ancient collagen sequence
data, is that notoungulates and litopterns (another extinct South American ungulate order)
are sister to Perissodactyla. To test these starkly different alternatives, as well as the
hypothesis implicit in both that Notoungulata is monophyletic, I built on a published
large total-evidence matrix that was built to test placental interordinal relationships. I
added seven notoungulate and one litoptern species, a 10% taxon sampling increase. I
expanded character sampling, adding two morphological characters often used in
notoungulate intraordinal systematics, one dental and one cranial, and I added the
recently published collagen loci that had linked notoungulates and litopterns to
Perissodactyla. In multiple analyses of the total-evidence dataset and its partitions, my
results show that notoungulates form a clade sister to Tethytheria, supporting the
morphological hypothesis and overturning the hypothesis based only on the collagen
data. Intriguingly, nested consistently within the notoungulate clade in my results is an
extant taxon that also has oscillated from Perissodactyl to Afrothere: hyraxes. Molecular
data put hyraxes in Paenungulata (Afrotheria); I found new morphological character
support for this, and for the placement of Notoungulata.

“In testing affinities of fossil taxa, morphology retains critical importance even in light of
ancient molecular data. My results also reinforce the value of well-constructed homology
statements and thorough taxon sampling.”

Note that West 2017

  1. Bemoans the lack of DNA for this purported clade, not realizing that DNA analyses do not bring insight to morphological studies, but constantly confuse topologies.
  2. Discusses characters like cursoriality, but those have no business in analysis.
  3. Tests the concept of a monophyletic Notoungulata. Thats’ good! Recovers a monophyletic notoungulata. That’s probably due to taxon exclusion. Many former notoungulates now nest with marsupial wombats.
  4. Recovered hyraxes with purported notoungulates, not with elephants and manatees. This is a red flag showing some sort of error in the data set.
  5. Does not list the genera sampled.
  6. Recovers Afrotheria. That’s probably due to the DNA in the dataset.

West should
remove DNA characters, add many more fossil taxa (including wombats) and report findings afterwards. That we’d all like to see.

West AR 2017. Resolving the affinities of Notoungulata; Character selection, taxon sampling,and the influence of ancient molecular data. SVP abstracts 2017.

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