Avila and Mothé 2021 try to show how South American wombats (marsupials) arose from African hyraxes (placentals)

Once again,
paleontologists are excluding taxa, testing genes and recovering untenable results.

Unfortunately Avilla and Mothé 2021 used genetic studies
to show South American marsupial wombats, like Pyrotherium (Fig. 2), arose from African placental hyraxes (Procavia and kin, Fig. 3). Astrapotheres (Fig. 4) were also added to this recipe of unrelated taxa.

the authors cherry-picked a short list of taxa following current university textbooks and lectures. That means they excluded a raft of pertinent taxa that would have separated these clades.

From the Avila and Mothé 2021 abstract:
“The South American native ungulates (SANUs) are usually overlooked in Eutherian phylogenetic studies. In the rare studies where they were included, the diversity of SANUs was underrated, keeping their evolutionary history poorly known. Some authors recognized the SANUs as a monophyletic lineage and formally named it Meridiungulata.”

According to Wikipedia
Meridiungulata is an extinct clade with the rank of cohort or superorder, containing the South American ungulates Pyrotheria (possibly including Xenungulata), Astrapotheria, Notoungulata and Litopterna. It is not known if it is a natural group; it is known that both Litopterna and Notoungulata form a clade based on collagen evidence, but the placement of the other members is uncertain. it was erected to distinguish the ungulates of South America from other ungulates.”

Earlier the LRT split up members of the traditional and now defunct clade, Notoungulata. It split apart the pyrotheres from the astrapodtheres and split the litopterns as well.

Figure 1. Cladogram from Avila and Mothé 2021. Color overlays added here. Some fragmentary taxa based on dentition (the clade of red branches) I’m not going to guesstimate.

According to a wide gamut trait-based phylogenetic analysis,
the large reptile tree (LRT,1880+ taxa), members of the Pyrotheria (Fig. 2) are marsupial diprotodont wombats, not placentals. Members of the Liptoterna, like Macrauchenia, are chalicothere sisters (close to living perissodactyls). Members of the Astrapotheria are related to phenacodontids (basal hoofed placentals) and Titanoides.

So if Avila and Mothé are linking these unrelated taxa together
based on DNA, we have one more example of continental viruses infecting and skewing phylogenetic analyses (e.g. Afrotheria, Laurasiatheria, etc).

Figure 3. Pyrotherium is a marsupial, not a relative to Notostylops, contra Billet 2010.
Figure 2. Pyrotherium is a diprotodont (wombat) marsupial in the LRT.

Continuing from the Avila and Mothé 2021 abstract:
“Here, we recognized and defined a new supraordinal lineage of Eutheria, the Sudamericungulata, after performing morphological phylogenetic analyses including all lineages of SANUs and Eutheria. The SANUs resulted as non-monophyletic; thus, Meridiungulata is not a natural group; Litopterna and “Didolodontidae” are Panameriungulata and closer to Laurasiatheria than to other “Meridiungulata” (Astrapotheria, Notoungulata, Pyrotheria, and Xenungulata).”

No Eutheria = Placentalia, so wombats (= Pyrotherium, Fig. 2) are not members.
Yes Liptoterns are perissodactyl placentals, so not closely related to pyrothere marsupials.
Mixed Some traditional notoungulates are placentals in the LRT, others are marsupials. This is why it is a good idea to avoid suprageneric statements based on defunct clades, if possible.

Figure 3. Skeleton of a hyrax (Provavia).
Figure 3. Skeleton of a hyrax (Provavia). Yes, it looks kind of like a wombat, but it is not one.

Continuing from the Avila and Mothé 2021 abstract:
“The other “Meridiungulata” is grouped in the Sudamericungulata, as a new monophyletic lineage of Afrotheria Paenungulata, and shared a common ancestor with Hyracoidea.”

This is false. See the LRT for hyrax ancestors and descendants, none of which are marsupials. This is why we all need to minimize taxon exclusion and avoid deep time genomic studies. Too often DNA studies lead to messes like this, promoting geographic viruses over physical traits.

Figure 4. Astrapotherium to scale with two specimens of Meniscotherium.
Figure 4. Astrapotherium to scale with two specimens of Meniscotherium.

Continuing from the Avila and Mothé 2021 abstract:
“The divergence between the African and South American lineages is estimated to Early Paleocene, and their interrelationships support the Atlantogea (Ezcurra and Agnolin 2012) biogeographic model.”

Let’s not forget that there was a post-Cretaceous faunal exchange between three linked southern continents: South America, Antarctica and Australia. At the same time there was a growing Atlantic Ocean between South America and Africa. The Atlantogea hypothesis (Ezcurra and Agnolin 2012) is not supported by the LRT.

All deep time genomic studies (so far) have been wastes of time and effort.
By that I mean, the resulting sister taxa too often don’t look anything like one another. And they should resemble one another if they are related to one another. Endemic viruses affect DNA testing and split clades into geographic areas, too often gathering dissimilar local taxa together. Just look at the Avila and Mothé 2021 results linking rodents with ungulates and hyraxes with wombats.

Colleagues, please put away your test tubes full of genes
and start building a wide-gamut, trait-based phylogeny, like the LRT. Then you will have the powerful tool you’ve been looking for, one you can use for the rest of your life to avoid the untenable and scientifically embarrassing results recovered in most, if not all current deep time genomic tests.

Avilla LS and Mothé D 2021. Out of Africa: A New Afrotheria Lineage Rises From Extinct South American Mammals. Frontiers in Ecology and Evolution 9:654302.
doi: https://doi.org/10.3389/fevo.2021.654302
Ezcurra MD and Agnolin F 2012. A New Global Palaeobiogeographical Model for the Late Mesozoic and Early Tertiary. Systematic Biology 61(4):553–566.


2 thoughts on “Avila and Mothé 2021 try to show how South American wombats (marsupials) arose from African hyraxes (placentals)

  1. If you read more than the abstract (and note the full paper is free), you would have seen the authors only used morphological characters, not molecular data.

    • Pretty obvious, Mickey, considering the long list of fossil taxa employed. That the authors placed the genomic clade, Afrotheria, in their title is their indication that the basis for their abbreviated cladogram was genomic (and therefore flawed). Adding just a few cherry-picked fossil taxa does not help, as the results indicate. Defending the Avila and Mothé results, by your silence on that subject, is illuminating. Thanks for your readership.

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