Ever hear of Palaeothentes?

Currently there is no Wikipedia page for this taxon.
Even so, I found it to be far more important at filling gaps and shaking up paradigms than it seemed at first. The small, dull-looking taxa tend to be like that, as readers now know.

You could find this rat-sized Miocene taxon
(Fig. 1) in Carroll’s 1988 book, Vertebrate Paleontology, now well-worn and in pieces due to constant page flipping and scanning. Today’s research has revealed several more precise and more recent resources.

According to Abello and Candella 2010,
Palaeothentes minutes (Ameghino 1887) is a paucituberculatan (details below) from the Santa Cruz Formation The results indicate that Palaeothentes would have been an agile cursorial dweller, with leaping ability, similar to the extant paucituberculatan Caenolestes fuliginosus and the didelphid Metachirus nudicaudatus.”

Okay, so now we have a problem.
In the large reptile tree (LRT, 1445 taxa) Caenolestes is not a marsupial. It nests with Rhyncholestes and more distantly Apatemys and more distantly, the extant tree shrew, Tupaia and the extant shrew, Scutisorex. As noted earlier, shrew opossums are placental shrews, not marsupial opossums in the LRT.

Wikipedia reports,
“Like several other marsupials, they do not have a pouch, and it appears that females do not carry the young constantly, possibly leaving them in the burrow.”
That’s describes most rodent/rabbit/tree shrew mothers and their young.

Wikipedia reports,
“Paucituberculata is an order of South American marsupials. Although currently represented only by the eight living species of shrew opossums, this order was formerly much more diverse, with more than 60 extinct species named from the fossil record, particularly from the late Oligocene to early Miocene epochs.”

Let’s solve that problem
by adding Palaeothentes to the LRT. Doing so recovers this taxon at the base of the Apatemys + Trogosus clade, next to the clade that includes Caenolestes, within Glires, far from Marupialia.

I suspect taxon exclusion
is the cause for the present lack of confirmation for traditional consensus. Many PhDs over several decades have followed tradition in nesting and testing shrew opossums with marsupials without testing them against apatemyids apparently. That’s why the LRT is here, to test taxa that have never been tested together before.

But wait! There’s a novel twist here~~~~~~!
Carroll 1988 reports, “Caenolestids have long been recognized as being very distinct from other South American marsupials, but they share with them a highly distinctive pattern of the spermatozoa, which become paired within the epididymis. Paired sperm are not known in any placental groups or among the Australian marsupials.” 

Sorry.
Physical traits have to trump genes and sperm. It just has to be that way because the LRT includes fossil taxa, which never preserve sperm. There have to be rules that all participants abide by. Interesting that the gene for paired spermatozoa is localized to one continent, just as genes separate other placentals into afrotheres and laurasiatheres. By the way, “The data show that paired spermatozoa exhibit a significant motility advantage over single spermatozoa in a viscous medium” according to Moore and Taggart 1995, who tested Monodelphis, a South American opossum.

Finally
we have a last common ancestor for arboreal Apatemys (Eocene, North America) and terrestrial Trogosus (Eocene, North America), two former enigma taxa with little to no relationship with other better known mammal clades. All members of Glires had their genesis sometime in the Jurassic, based on the presence of highly derived multituberculates (clade: Glires) in the Jurassic.

Wikipedia considers
apatemyids and trogosinae (Tillodontia) to be members of the Cimolesta, “an extinct order of non-placental eutherian mammals.” This bungling of the mammal family tree is due to taxon exclusion and the lack of a phenomic (trait-based) wide gamut cladogram that includes all the taxa present in the LRT. Paleontology needs to toss off a wide range of useless tradition with a reptile revolution led by someone out there confirming (or refuting) the widest gamut cladogram presently available: the LRT.

Palaeothentes lemoinei (Ameghino 1887, MPM-PV 3566; Miocene) was considered a prehistoric shrew opossoum (clade: Paucituberculata) but here nests next to shrew opossums, at the base of the Apatemys + Trogosus clade within Glires. The skull is 2x wider than tall, the canines are still large, the last premolar is large with a flat occlusal surface and the nasals split to form a zigzag suture with the frontals.

References
Abello MA and Candela AM 2010. Postcranial skeleton of the Miocene Marsupial Palaeothentes(Paucituberculata, Palaeothentidae): Paleobiology and Phylogeny. Journal of Vertebrate Paleontology 30(5):1515-1527.
Ameghino F 1887. Enumeracions sistematicad e las especies de mamiferos
fosiles coleccionados por Carlos Ameghino en los terranos eocenos de la Patagonia austral y depositados en el Museo La Plata. Boletin Museo de La Plata, 1:1-26.
Carroll RL 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Co. New York.
Forasiepi AM, Sánchez-Villagra MR, Schmelzle T,  Ladevèze S and Kay RF 2014. An exceptionally well-preserved skeleton of Palaeothentes from the Early Miocene of Patagonia, Argentina: new insights into the anatomy of extinct paucituberculatan marsupials. Swiss Journal of Palaeontology, 133(1):1-21.
Moore HD and Taggart DA 1995. Sperm pairing in the opossum increases the efficiency of sperm movement in a viscous environment. Biol. Reprod. 52(4):947-53.
Osgood WH 1921. A monographic study of the American marsupial, Caenolestes. Field Museum of Natural History, Zoological series 14:1–156.

wiki/Apatemyidae
wiki/Paucituberculata
https://en.wikipedia.org/wiki/Shrew_opossum
wiki/Vertebrate_Paleontology_and_Evolution

Paucituberculata -Trouessart 1898, Ameghino 1894

There was some news
about Palaeothentes recently (see below). Note, the experts consulted here consider this genus a marsupial.

New Bolivian Marsupials from the Middle Miocene