Microsyops enters the LRT between three overlooked shrew opossums

Silcox, Gunnell and Bloch 2020
described the cranium of Microsyops annectens (Leidy 1872, Marsh 1872, Fig. 1), but were not able to nest it phylogenetically due to taxon exclusion. The authors mistakenly kept calling it a plesidapiform and mistakenly considered plesiadapiforms ‘plausible stem primates.’

More taxa
solve this problem.

Figure 1. Micrsyops skull from Silcox et al. 2020. The third tooth is the canine.

Figure 1. Micrsyops skull from Silcox et al. 2020. The third tooth is the canine.

From their abstract:
“While results from phylogenetic analyses support euarchontan affinities, specific relationships of microsyopids to other plesiadapiforms (plausible stem primates), Euprimates (crown primates), Scandentia (treeshrews), and Dermoptera (colugos) are unresolved.”

From the discussion and conclusions:
“The basicranial anatomy of microsyopids does not provide evidence in support of a clear link to any of the extant euarchontans, and suggests that the primitive morphology of this region in Euarchonta was little differentiated from that observed in the primitive placental mammals.”

Figure 1. Not a marsupial, and not a shrew opossum, Palaeothentes nests in the LRT at the base of the Apatemys + Trogosus clade nest to the clade of living shrew opossums within Glires.

Figure 2. Not a marsupial, and not a shrew opossum, Palaeothentes nests in the LRT at the base of the Apatemys + Trogosus clade nest to the clade of living shrew opossums within Glires.

By contrast
in the large reptile tree (LRT, 1698+ taxa) using fewer traits and more taxa, Microsyops nests as a near basal member of Glires (gnawing mammals) between three traditional pouchless ‘marsupials’, the two extant shrew ‘opossums’, Rhyncholestes (Fig. 3) + Caenolestes and Palaeothentes (Miocene. Fig. 2). These nest at the base of Trogosus (Eocene) + the Apatemyidae (Eocene). None of these taxa, other than Apatemys, were included in the Silcox et al. cladograms.

Figure 1. Skull of Rhyncholestes along with in vivo photo.

Figure 3. Skull of Rhyncholestes along with in vivo photo.

Ironcally, ten years earlier,
Silcox, Bloch, Boyer and Houde (2010) wrote: “Microsyopids are the most similar to apatemyids in the basic form of the basicranium of any ‘plesiadapiform’.

Again, adding taxa
(more rodents, rabbits and shrew opossums ) solves this problem. Don’t assume pouchless shrew opossums are marsupials. In the LRT they are gnawing placentals, derived from tree shrews, as we learned earlier here. Call them marsupial-mimics.


References
Leidy J 1872.
Remarks on fossils from Wyoming: Proceedings of the Academy of Natural Sciences, Philadelphia 1872: 19–21.
Marsh OC 1872. Preliminary description of new Tertiary Mammals. Parts I– IV: American Journal of Science 4: 122–128, 202–224.
Silcox MT, Bloch JI, Boyer DM and Houde P 2010. Cranial anatomy of Paleocene and Eocene Labidolemur kayi (Mammalia: Apatotheria), and the relationships of the Apatemyidae to other mammals. Zoological Journal of the Linnean Society160: 773–825.
Silcox MT, Gunnelll GF and Bloch JI 2020. Cranial anatomy of Microsyops annectens (Microsyopidae, Euarchonta, Mammalia) from the middle Eocene of Northwestern Wyoming. Journal of Paleontology, 28pp. 0022-3360/20/1937-2337
doi: 10.1017/jpa.2020.24

wiki/Microsyops

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