Vincelestes neuquenianus (Bonaparte 1986, Rougier, Wible and Hopson 1992, Early Cretaceous, 130 mya). Although Vincelestes is ancient and therefore primitive, the hyper-enlarged premolar fangs, loss of the canine, small tooth count and short rostrum indicate a highly derived taxon. Nine individuals are known. Skeleton is probably a chimaera of several specimens and the degree of completion is unknown. The tail is extraordinarily long and provided with deep chevrons.  µCT scan of the skull mage from Digimorph.org and used with permission.

Ambolestes zhoui (Bi et al. 2018, Early Cretaceous, 126 mya; 25cm in length) is is one third the size of the extant opossum, Didelphis. In the LRT nests Ambolestes close to Eomaia, but clloser to Vincelestes.

Bi said in an interview, “Ambolestes zhoui is an early member of the placental lineage. It also carries mixed features both placentals and marsupials”. That is supported by the LRT.

Bi S-B, Zheng X-T, X, Wang X-L, Cignetti N-E, Yang SL and Wible JR 2018. An Early Cretaceous eutherian and the placental/marsupial dichotomy. Nature (advance online publication) DOI: https://doi.org/10.1038/s41586-018-0210-3
https://www.nature.com/articles/s41586-018-0210-3

Bonaparte JF 1986. Sobre Mesungulatum houusayi y nuevos mamíferos Cretácicos de Patagonia, Argentina [On Mesungulatum houssayi and new Cretaceous mammals from Patagonia, Argentina]. Actas del IV Congreso Argentino de Paleontología y Biostratigrafía 2:48-61.

Carroll, RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.

Marsh OC 1872. Preliminary description of new Tertiary mammals. American Journal of Science and Art, 4: Part I: 122-128, Part 11-IV: 202-224.

Matthew WD 1906. The Osteology of Sinopa, a Creodont Mammal of the Middle Eocene. Proc. U. S. Nat. Mus., 30:203-233, pl. XVI, and text figs. 1-20.

Matthew WD 1909. The Carnivora and Insectivora of the Bridger Basin, middle Eocene. Memoires of the American Museum of Natural History, 9: 289-567.

Morlo M and Gunnell GF 2003. Small limnocyonines (Hyaenodontidae, Mammalia) from the Bridgerian Middle Eocene of Wyoming: Thinocyon, Prolimnocyon, and Iridodon, new genus. Contributions from the Museum of Paleontology, The University of Michigan31(2):43–78.

Rougier GW, Wible JR and Hopson JA 1992. Reconstruction of the cranial vessels in the Early Cretaceous mammal Vincelestes neuquenianus: implications for the evolution of the mammalian cranial vascular system. Journal of Vertebrate Paleontology 2:188–216. https://doi.org/10.1080/02724634.1992.10011449

wiki/Vincelestes
wiki/Ambolestes