Caluromys vs Vulpavus vs Ptilocercus

At the base of the Eutheria (placental mammals)
nests the small, extant, didelphid marsupial Caluromys. So it’s worthwhile to put the skulls of a few basal placentals next to Caluromys to see what the similarities and differences are.

Vulpavus comparison
In the large reptile tree (LRT, 1272 taxa) Caluromys nests with Vulpavus (Fig. 1, Eocene; Marsh 1871), a basalmost member of the placental clade, Carnivora. Two molars characterize this clade. Juvenile Caluromys (Fig. 2; Flores, Abdala  and Giannini 2010) also have two molars.

Figure 1. Vulpavus compared to Caluromys skulls in lateral view.

Figure 1. Vulpavus compared to adult Caluromys skull in lateral view. These two taxa nest together in the LRT.

Ptilocercus comparison
(pen-tailed tree shrew, extant, Le Gros-Clark 1926) is best compared, both in size and morphology to the juvenile Caluromys (Fig. 2). Though not a permanent member of the LRT, a test nested the juvenile Caluromys with Ptilocercus.

Figure 2. Ptilocercus (pen-tailed tree shrew) compared to Caluromys (wooly-opossum) young juvenile from Flores, Abdala and Giannini 2010.

Figure 2. Ptilocercus (pen-tailed tree shrew) compared to Caluromys (wooly-opossum) young juvenile from Flores, Abdala and Giannini 2010.

Caluromys derbianus (Allen 1904; Flores, Abdala and Giannini N 2010, Fonseca and Astúa 2018. ) is the living ‘wooly opossum’, native to Central America. This taxon nests just inside of the first placental clade, Carnivora, despite retaining a marsupium (pouch). It is an omnivore, as in related basal Carnivora, like Nandinia.

Juvenile skulls have only two molars, the same as those found in Vulpavus (below) and other Carnivora, so this trait is neotonous in Carnivora.

That Caluromys is closely related to basal placental taxa is strong… and heretical.
Earlier we looked at skull similarities between Caluromys and the fruit bat, Pteropus.

Allen JA 1904. Mammals from southern Mexico and Central and South America. Bulletin American Museum of Natural History 20(4): 29-80.
Flores DA, Abdala F and Giannini N 2010. Cranial ontogeny of Caluromys philander (Didelphidae: Caluromyinae): a qualitative and quantitative approach. Journal of Mammalogy 91(3):539–550.
Fonseca R and Astúa D 2018. Geographic variation in Caluromys derbianus and Caluromys lanatus (Didelphimorphia: Didelphdiae) Zoologica 32(2):109–122.
Heinrich RE and Rose KD 1997. Postcranial morphology and locomotor behavior of two early Eocene miacoid carnivorans, Vulpavus and Didymictis. Palaeontology 40:279-305
Le Gros-Clark WE 1926. On the Anatomy of the Pen-tailed Tree-Shrew (Ptilocercus lowii.) Proceedings of the Zoological Society of London 96: 1179-1309.
DOI – 10.1111/j.1096-3642.1926.tb02241.x
Marsh 0C 1871. Notice of some new fossil mammals and birds from the Tertiary formations of the West. American Journal of Science, Series 3, 2: 120-127



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