Monodelphis sorex (Burnett 1830, Pine et al. 2013) is the extant southern red-sided opossum. It is found on the Atlantic coast of South America. No pouch is present. The young cling to their mother's nipples, then, when older, ride on her back. Postfrontals are retained on this smaller taxon, missing in Monodelphis domestica.

Pucadelphys andinus (Marshall and de Muizon 1988; Marshall, de Muizon and Sigogneau-Russell 1995; Early Paleocene; 10cm snout-vent length) is an extinct marsupial basal to the sabertooth clade. It is known to be gregarious from a rare collection of twelve females, six males and five late stage juveniles. The tiny in situ fossil is shown life size above on a 72 dpi monitor.

Didelphodon vorax (Marsh 1889; Wilson et al. 2016; Late Cretaceous 80mya; 12 cm skull length) was a predator with blade-like cutting teeth and bulb-like crushing teeth. It had a long neck and short limbs. With such traits Didelphodon could have been an otter-like mollusc shell crusher. Wilson et al. tested only Cretaceous and Palaeogene taxa. They used many dental trait and nested Didelphodon closest to Borhyaena among tested taxa. Here Didelphodon nests in the Hadrocodium clade.

Mayulestes feox (Muizon 1994; 64 mya; MNHC P 1249; scale bar = 5cm) is a Palaeocene marsupial basal to Didelophodon. It was originally considered a borhyaenoid. Here it nests within the tiny flat-head marsupial clade close to Hadrocodium.

Asiatherium reshetovi (Trofimov and Szalay 1994, Szalay and Trofimov 1996; PIN 3907; Late Cretaceous; 80mya) is a key Mongolian metathere close to Mayulestes, but smaller. Note the flat skull and dorsal orbits. Shown in situ below.

Ameghino F 1892. (Issued in 1894.) Enumeration synoptique deses pesces de mammiferes fossilesdes formation sócénes de Patagonie. Boletindela, Academia Nacionalde Cienciasen Cordoba, XIII, p.259 (p.108 in reprint).

Burnett GT 1830. Illustrations of the Quadrupeda, or Quadrupeds, being the arrangement of the true four-footed Beasts indicated in outline. Quarterly Journal of Science, Literature and Art, July to December, 1829, 336–353.

Cope ED 1875. On the Supposed Carnivora of the Eocene of the Rocky Mountains. Proceedings of the Academy of Natural Sciences, Philadelphia. pp. 444–449.

Gregory WK and Simpson GG 1926. Cretaceous mammal skulls from Mongolia. American Museum Novitates 225, 7-20.

Marsh OC 1889. Discovery of Cretaceous Mammalia, part i, ii. American Journal of Science, Series 3 38: 81–92; 177–180.

Marshall LG and Muizon C de 1988. The dawn of the age of mammals in South America. National Geographic Research 4 (1): 23-55.

Marshall LG, de Muizon C and Sigogneau-Russsell D 1995. Pucadelphys andinus (Marsupialia, Mammalia) from the early Paleocene of Bolivia. Part I: The locality of Tiupampa: age, taphonomy and mammal fauna. Mémoires du Muséum national d'histoire naturelle 165: 11–20.

de Muizon C 1994. A new carnivorous marsupial form the Palaeocene of Bolivia and the problem of marsupial monophyly. Nature 370:208–211.

Pine RH, Flores DA and Bauer K 2013. The second known specimen of Monodelphs unistriata (Wagner) (Mammalia: Didelphimorphia), with redescription of the species and phylogenetic analysis. Zootaxa3640 (3):425-441.

Trofimov BA and Szalay FS 1994. New Cretaceous marsupial from Mongolia and the early radiation of Metatheria. Proceedings of the National Academy of Sciences 91:12569-12573

Wilson GP, Eddale EG, Hoganson JW, Calede JJ and Vander Linden A 2016. A large carnivorous mammal from the Late Cretaceous and the North American origin of marsupials. Nature Communications 7:13734 PDF

wiki/Monodelphis.sorex
wiki/Didelphodon
wiki/Asiatheriium
wiki/Mayulestes
wiki/Pucadelphys