Goodbye Xenarthra: no longer monophyletic in the LRT

This post reinforces and supports
an earlier post that was pulled, then republished, as work proceeded on updating all the taxa in and around the traditonal Xenarthra

According to Wikipedia – Xenarthra
“…is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths. Xenarthrans originated in South America during the late Paleocene about 60 million years ago.”

According to the large reptile tree
(LRT, 2336 taxa, subset Fig 1) the tube-snouted xenarthrans (armadillos, anteathers) now arise from Leptictis (Fig 2) currently known from the Eocene of North America. Those xenarthrans with a more boxy snout (sloths, glyptodonts) arise from Barylambda currently known from the Paleocene of Wyoming.

Armor and simple teeth arose by convergence in both groups.

Outgroups to Xenarthra1 include Pholidocercus from the Messel pits of Europe.

Outgroups to Xenarthra2 include sengis (Rhynchocyon) and aardvarks (Orycteropus) in the LRT. Both are from Africa. So taxa likely joined adapids and others taking a Cretaceous land bridge from Asia to North America (the same one psittacosaurs and tyrannosaurs took), and then to South America.

According to Wikipedia – Xenarthra
“Their relationship to other placental mammals is obscure.”

No longer obscure after testing a wide gamut of candidates.

“Xenarthrans share several characteristics that are not present in other placental mammals, which suggest that xenarthrans descend from subterranean diggers.”

Let’s not ‘pull a Larry Martin’ here. Don’t focus on traits. Those will make themselves known AFTER running an analysis to recover the last common ancestor(s). Some traits converge. The last common ancestor method actually models evolutionary events.

“1. extra articulations that are unlike other mammals.
2. The ischium of the pelvis is also fused to the sacrum of the spine.
3. Xenarthran limb bones are typically robust, with large processes for muscle attachment. 4.  Relative to their body size, living xenarthrans are extremely strong.
5. Their limb bone structures are unusual.
6. They have single-color vision.
7. The teeth of xenarthrans are unique.”

Sounds like a great list. Trouble is these arose twice (or more) in the LRT.

“Xenarthrans are also often considered to be among the most primitive of placental mammals”

Yes and no. See figure 1.

“Females show no clear distinction between the uterus and vagina, and males have testicles inside the body, which are located between the bladder and the rectum.”

Also true of hedgehogs, odontocetes and tenrecs.

“Xenarthrans have the lowest metabolic rates among therians.”

Good to know. Make that twice by convergence. Surely some are lower than others.

According to Wikipedia – Xenarthra
“Xenarthrans were previously classified alongside the pangolins and aardvarks in the order Edentata (meaning toothless, because the members do not have incisors and lack, or have poorly developed, molars).”

Again: avoid ‘pulling a Larry Martin’ by focusing on shared traits. Better to run the analysis to recover last common ancestors. That’s how clades are defined.

“Subsequently, Edentata was found to be a polyphyletic grouping whose New World and Old World taxa are unrelated, and it was split up to reflect their true phylogeny.’

Be wary anytime you see this phrase: ‘true phylogeny’. In science every hypothesis is falsifiable. The LRT is falsifiable and it just falsified Wikipedia’s ‘true phylogeny.’

“Aardvarks and pangolins are now placed in individual orders, and the new order Xenarthra was erected to group the remaining families (which are all related)”

Not all related according to the LRT (Fig 1).

According to Wikipedia – Xenarthra
“The morphology of xenarthrans generally suggests that the anteaters and sloths are more closely related to each other than either is to the armadillos, glyptodonts, and pampatheres; this idea is upheld by molecular studies.”

By contrast, according to trait analysis (Fig 1) anteaters are closer to armadillos, while sloths are closer to glyptodonts. If the falsified interrelationship promoted by Wikipedia is upheld by molecular studies, that’s one more nail in the coffin of deep time molecular studies.

BTW, you can test both competing hypotheses yourself, as I just did. This is the essence and core of science: the scientific method. Let us know what you get!

Earlier studies (see below) hinted at the xenarthran split.

Final note:
For those who think the term ‘falsified’ means for good and forever… it does not. Substitute the term ‘more parimonious’ or ‘improved’ or ‘better’. Currently the mammal subset of the LRT has been ‘improved’ 300x over 300 days. And the work is not yet done. Convergent traits, like those seen in mysticetes and odontocetes, marsupial moles and golden moles, and the two xenarthran clades makes the reconstruction of the most parsimonious family tree of mammals difficult, but not impossible, as shown here (Fig 1).

Relying on deep time genomics is no help. Genes ignore fossil taxa and produce false positives that cannot be reproduced using trait analyses.

References
wiki/Xenarthra

The origin of glyptodonts – not from armadillos

Little Leptictis and Armored Holmesina nest closer now in the LRT

Look no further for a Xenarthran ancestor: It’s been Barylambda all along.

Source: https://pterosaurheresies.wordpress.com/2025/02/10/goodbye-xenarthra-no-longer-monophyletic-in-the-lrt/