Rhyncholestes: it’s supposed to be a marsupial…

…but Rhyncholestes raphanurus (Osgood, 1924; long-nosed shrew-opossum, Chilean shrew opossum, extant; snout-vent length 20cm), nests in the large reptile tree (LRT, 1259 taxa) between the squirrel-like tree shrew, Apatemys, and a large living shrew, Scutisorex, all within the placental clade, Glires. Wikipedia and other sources consider this shrew-like South American mammal a marsupial, but Wiki also notes that Rhyncholestes lacks a marsupium (pouch). Females have seven nipples.

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

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

Rhyncholestes appears to be terrestrial,
nocturnal and an omnivore with a very restricted range (central Chile). Unlike the common shrew, Scutisorex, Rhyncholestes has a complete zygomatic arch and 3 large molars + a fourth vestige molar. That may be why it was considered a marsupial… but that would be pulling a Larry Martin in the LRT, where you need hundreds of traits to determine where a taxon nests.

 

Figure 1. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable.

Figure 2. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable. More to the point of today’s blogpost, fewer teeth on a shorter rostrum here than on Rhyncholestes, but otherwise, scores about the same in the LRT.

References
Osgood WH 1924. Review of living caenolestids with description of a new genus from Chile. Field Museum of Natural History Zoological Series 14, 165–173.

wiki/Long-nosed_caenolestid
https://sib.gob.ar/ficha/ANIMALIA*rhyncholestes*raphanurus

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