Two carnivorous marsupials, Thinocyon and Limnocyon, enter the LRT

Meet Thinocyon and Limnocyon,
(Figs 1, 2) two Eocene marsupials recovered from North America and known for over a century.

Figure 1. Thinocyon skull shown in several views.

Thinocyon medius
(Marsh 1872, Matthew 1909, Morlo and Gunnell 2003, Eocene) was traditionally considered a small limnocyonine (Fig 2) hyaenodontid mammal, but here nests with Vincelestes (Fig 4) among the basal creodont (= carnivorous) marsupials. According to Morlo and Gunnell: “Limnocyoninae are relatively small hyaenodontid creodonts characterized by reduction and loss of upper and lower third molars.”

In the LRT Limnocyon is not closely related to Hyaenodon (Fig 3). Vincelestes is generally omitted from discussion of these two new additions to the LRT and is not considered a marsupial by the authors of Wikipedia, but outside the placental – marsupial dichotomy. In the LRT placentals are derived from marsupials like Monodelphis and Chironectes.

Figure 2. Limnocyon enters the LRT as a sister to Thinocyon and Vincelestes.

Limnocyon verus
(Marsh 1872) is known from a complete skull and mandibles, plus a few uncrushed post-cranial bones.

Here
in the large reptile tree (LRT, 2215 taxa, subset Fig 3) Thinocyon (Fig 1) and Limnocyon (Fig 2) nest together close to Early Cretaceous Vincelestes, at the base of the sabertooth marsupials.

Figure 3. Subset from the LRT focusing on carnivorous marsupials and now including Thinocyon and Limnocyon.

According to Wikipedia,
“Limnocyonidae (“swamp dogs”) is a family of extinct predatory mammals from extinct order Hyaenodonta. Fossil remains of these mammals are known from late Paleocene to late Eocene deposits in North America and Asia. Limnocyonids had only two molars in the upper and lower dentition.”

Figure 4. Middle Miocene housecat-sized Patagosmilus and rat-sized Early Cretaceous Vincelestes at full scale on a 72dpi monitor. These are small members of the sabertooth marsupial clade.

Unfortunately due to taxon exclusion
traditional workers still don’t realize limnocyonids are distinct from hyaenodonts and both are marsupials.

Adding taxa resolves all enigmas according to results recovered in the LRT.

References
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.
Forasiepi AM and Carlini AA 2010. A new thylacosmilid (Mammalia, Metatheria, Sparassodonta) from the Miocene of Patagonia. Zootaxa. 2552, ss. 55–68, 2010 (Ing.)
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 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.

wiki/Vincelestes
wiki/Patagosmilus
wiki/Thinocyon – not yet posted
wiki/Limnocyonidae
wiki/Vincelestes