The little kangaroo mimic, Proargyrolagus, finds new nesting partners in the LRT

It looked like a little kangaroo,
but Late Oligocene South American Proargyrolagus (Fig 1) was convergent with those bigger Australian hoppers. After recent housekeeping this traditional enigma now nests with two extant quadrupedal mouse-like South American marsupials not known for hopping: Caenolestes and Rhyncholestes (Fig 3) in the large reptile tree (LRT, 2322 taxa).

Sanchez-Villagra and Kay 1997 reported,
“The Argyrolagidae are one of the most enigmatic extinct groups of South American mammals. Most of what is known about this group is based on the description by Simpson (1970a, b) of skulls, jaws, and postcrania of several highly specialized
Plio-Pleistocene species from Argentina.”

Figure 1. The skull of Proargyrolagus and an illustration of Argyrolagus. The traits shown here align very closely with Macropus, the kangaroo, to no one’s surprise… so why was this considered an enigma taxon? ” data-image-caption=”

Figure 1. The skull of Proargyrolagus and an illustration of Argyrolagus. The traits shown here align very closely with Macropus, the kangaroo, to no one’s surprise… so why was this considered an enigma taxon?

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/07/proargyrolagus_argyrolagus_5881.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/07/proargyrolagus_argyrolagus_5881.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-27366″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/07/proargyrolagus_argyrolagus_5881.jpg” alt=”Figure 1. The skull of Proargyrolagus and an illustration of Argyrolagus. The traits shown here align very closely with Macropus, the kangaroo, to no one’s surprise… so why was this considered an enigma taxon?” width=”584″ height=”430″ />

Figure 1. The skull of Proargyrolagus and an illustration of Argyrolagus. The traits shown here align very closely with Macropus, the kangaroo, to no one’s surprise… so why was this considered an enigma taxon?

Proargyrolagus bolivianus
(Wolff 1984; Late Oligocene) Simpson reported, “Argyrolagids are marsupials but show no clear affinity with any others known. They probably arose from didelphids independently of other known families and are distinct at the superfamily level, at least.”

Figure 1. Proargyrolagus skull compared to related taxa in the LRT, including extant Caeolestes. ” data-image-caption=”

Figure 1. Proargyrolagus skull compared to related taxa in the LRT, including extant Caeolestes.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/rhyncholestes_caenolestes_tarsipes_skull588.jpg?w=116″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/rhyncholestes_caenolestes_tarsipes_skull588.jpg?w=397″ tabindex=”0″ role=”button” class=”size-full wp-image-87538″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/rhyncholestes_caenolestes_tarsipes_skull588.jpg” alt=”Figure 1. Proargyrolagus skull compared to related taxa in the LRT, including extant Caeolestes. ” width=”584″ height=”1508″ />

Figure 2. Proargyrolagus skull compared to related taxa in the LRT, including extant Caeolestes.

According to Wikipedia – Argyrolagus
“Jumping on its hind legs, the 15–20-centimetre (5.9–7.9 in) long (without tail) Argyrolagus resembled a gerbil or kultarr. It had a long tail for balance, and a narrow head with a pointed snout. Judging from its huge eyes, Argyrolagus was nocturnal. The form of its teeth suggest that it would have fed on desert plants. A 2019 study confirmed that Argyrolagus was probably adapted for bipedal jumping and was probably also well adapted for digging.”

It’s modern relatives (Fig 3) are both insect eaters.

Rhyncholestes raphanurus 
(Osgood, 1924; long-nosed shrew-opossum, Chilean shrew opossum, extant; snout-vent length 20cm), lacks a marsupium (pouch) by convergence with pre-placentals like Monodelphis.

Figure 7. Rhyncholestes and Caenolestes are the most primitive living mammals with ear pinnae tested in the LRT. ” data-image-caption=”

Figure 7. Rhyncholestes and Caenolestes are the most primitive living mammals with ear pinnae tested in the LRT.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/04/caenolestes_rhyncholestes-invivo588.jpg?w=253″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/04/caenolestes_rhyncholestes-invivo588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-85278″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/04/caenolestes_rhyncholestes-invivo588.jpg” alt=”Figure 7. Rhyncholestes and Caenolestes are the most primitive living mammals with ear pinnae tested in the LRT.” width=”584″ height=”693″ />

Figure 3. Rhyncholestes and Caenolestes are the most primitive living mammals with ear pinnae tested in the LRT.

Caenolestes fuliginosus
(originally Hyracodon fuliginosus Tomes 1863) is the original shrew-opossum, the one that gave its name to the clade Caenolestidae. Note the fenestra between the nasal, frontal and maxilla.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

References
Abello MA and Candela AM 2020. Paleobiology of Argyrolagus (Marsupialia, Argyrolagidae): an astonishing case of bipedalism among South American mammals. Journal of Mammalian Evolution. 27 (3): 419–444.
Osgood WH 1921. A monographic study of the American marsupial, Caenolestes. Field Museum of Natural History, Zoological series 14:1–156.
Osgood WH 1924. Field Mus. Nat. Hist. Publ., Zool. Ser. 14:170.
Rougier GW, Apesteguía S and Gaetano LC 2011. Highly specialized mammalian skulls from the Late Cretaceous of South America. Nature. 479: 98–102.
Sanchez-Villagra MR 1997. The phylogenetic relationships of argyrolagid marsupials. Zoological Journal of Linnean Society 131(4):481–496.
Sanchez-Villagra MR and Kay RF 1997. A skull of Proargyrolagus, the oldest argyrolagid (Late Oligocene Salla Beds, Bolivia), with brief comments concerning its paleobiology. Journal of Vertebrate Paleontology 17(4):717-724.
Simpson GG 1970. The Argyrolagidae, extinct South American marsupials. Bulletin of the Museum of Comparative Zoology 139, 1–86.
Wolff RG 1984. A new early Oligocene argyrolagid (Mammalia: Marsupialia) from Salla, Bolivia. Journal of Vertebrate Paleontology 4:108-113.
Tomes PZS 1863. A small marsupial from Ecuador, named Hyracodon fuliginosus. Proceedings of the Zoological Society, London: 50–51.

wiki/Cronopio
wiki/Acristatherium
wiki/Caenolestes
wiki/Rhyncholestes
wiki/Paucituberculata
wiki/Honey_possum
wiki/Argyrolagus