Muribacinus

Muribacinus Temporal range: middle Miocene, 15.1-12.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Holotype and paratype specimens of Muribacinus.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Marsupialia
Order:	Dasyuromorphia
Family:	†Thylacinidae
Genus:	†Muribacinus
Species:	†M. gadiyuli
Binomial name
†Muribacinus gadiyuli Wroe, 1995

Muribacinus is an extinct genus of thylacinid that lived during the middle Miocene in what is now northwestern Queensland, Australia. It was described in 1995 from remains collected at the Riversleigh World Heritage Area. Only one species is known, M. gadiyuli.

Muribacinus was named in 1995 by Stephen Wroe based on fossils recovered from the Riversleigh World Heritage Area, northwestern Queensland. The holotype, QMF 30836, is a partial right maxilla and jugal collected from the Gag site. A right dentary from Henk’s Hollow site was assigned to the genus based on the proportions of the molar's shearing crests.^[1]

The generic name is a combination of the Waanyi word "muriba" (father) and the Ancient Greek stem word "-kynos" (dog), for the assumed classification as an early thylacinid species. The specific name comes from the Waanyi word “gadiyuli” (little).^[1]

Although smaller than most thylacinids, Muribacinus would have been similar in size to the modern Tiger quoll. Wroe (2001) estimated its weight to have been 1.6 kg (3.5 lbs), while Rovinsky et al. (2019) gave it a slightly larger estimate of 1.6–1.7 kg (3.5-3.7 lbs).^[2][3]

The teeth of Muribacinus retain large protocone cusps and talonids. The paracone and metacone cusps have a large distance between them. On each molar, the metaconid cusps and the small shelf that runs along the labial side of the tooth (called the stylar shelf) aren't as small as in other thylacinids. The second premolar is larger than the third premolar. The crest in front of the paracone (known as the preparacrista) is longer relative to the lingual border of the metacone (postmetacrista) on the second and third molars.^[1]

The first phylogenetic analysis that included Muribacinus found it to be in a polytomy with Mutpuracinus, Nimbacinus and clade containing all other thylacinids.^[4] Subsequent studies throughout the years have, however, recovered conflicting results. Both Murray & Megirian (2000) and Yates (2015) have recovered as the basalmost member of Thylacinidae.^[5][6] In at least two phylogenetic analyses performed by Rovinsky et al. (2019), Muribacinus formed a minor clade with the early-middle Miocene taxa Ngamalacinus and Nimbacinus as a sister group to all other thylacinids.^[3]

In at least one phylogenetic analysis performed by Churchill et al. (2024), Muribacinus was found to be a non-thylacinid dasyuromorphian, specifically within a polytomy with a well supported clade containing Barinya, Tyarrpecinus, Myrmecobius and Dasyuridae.^[7]

Although not directly dated, both the Gag site and Henk’s Hollow site are thought to have been middle Miocene in age, with a date range of ~15.1 to 12.9 Ma.^[3] During this time, Australia's climate would have been relatively warmer and wetter than it is today.^[8] The terrestrial biome of Riversleigh at the time has been interpreted as either being open forest or rainforest.^[9]

Contemporaneous with Muribacinus was the medium-sized, hypercarnivorous thylacinid Wabulacinus macknessi, and the small to medium-sized thylacoleonids Wakaleo oldfieldi and Lekaneleo myersi.^[10][11] Differences in body size and vertical segregation have been suggested to have reduced competition between the two families.^[12] As a result of its pronounced metaconid cusps, Muribacinus is thought to have been an unspecialised faunivore that fed on small vertebrates and invertebrates.^[3]