New tiny overlooked Thylacine ancestor recovered in the LRT

Confession: I overlooked this taxon,Hapalodectes hetangensis IVPP V 12385 (Fig 1), for far too long. However, comparisons to the recently extinct Tasmanian tiger, Thylacinus (Fig 1) are warranted and rewarding. Little, largely ignored IVPP V 12385 from Paleocene/Early Eocene strata in China (55mya) and now nests with the larger, almost dog-like, long-legged recent predator from Australia in the large reptile tree (LRT, 2340 taxa).

I should have seen this earlier.

In the LRT Both are close to the recent dasyurids, as well as tiny Pucadelphys and giant Andrewsarchus. Long-legged Ukhaatherium is a deeper ancestor, so phylogenetic bracketing puts long legs on the intervening skull-only taxa, too.

Surprisingly, and uniquely(?) both sexes of the Tasmanian tiger had a pouch and it opened posteriorly. Perhaps the same was present in IVPP V 12385, Ukhaatherium and Andrewsaruchus. However and exceptionally, many dasyurids lack a pouch.

Scrappy Hapalodectes fossils are also reported from Wyoming.

According to Wikipedia, “The genus [Hapalodectes] was once suggested to be related to the Archaeoceti, such as Pakicetus, due to numerous similarities between the skull and tooth anatomies of the two genera. Now, however, Hapalodectes and other mesonychians are thought to be related to basal artiodactyls, while the Archaeoceti are now determined to be descended from more derived artiodactyls, like Indohyus, which are related to hippopotamuses and anthracotheres.”

The LRT does not support the above hypotheses.

Moreover, the two specimens tested in the LRT do not nest together, so are not congeneric. The 5235 specimen has a postorbital bar and so nests with Thylacosmilus, the marsupial sabertooth from South America.

According to Wikipedia, “the consensus of authors prior to 1982 was that the thylacinid family were related to the Borhyaenidae, a group of South American predators, also extinct, that exhibited many similar characteristics of dentition. A review published in 1982 compared the skeletal structure of these groups, concluding the tarsal bones show greater affinity with the dasyurmorphs, strongly supporting the later theory that any dental similarities emerged independently via convergent evolution. Thylacinidae is currently considered to be sister to all other lineages within Dasyuromorpha, and is estimated to have split from other dasyuromorphs around 42-36 million years ago.”

The LRT supports the latter hypothesis.

The matching of IVPP V 12385 with Thylacinus (Fig 1) appears to bea novel hypotheses of interrelationships. If not, please provide a citation so I can promote it here.

Let’s also get a grad student to do a universal Hapalodectes study to lump and split them and also match them with unexpected taxa as warranted in their own large mammal tree.

Side Note: You may have noticed paragraph and line spacing formats have changed here. Apparently that’s a new WordPress code thing. I have tried to work around it, but (so far) have failed to do so. The new code/format imposes unwanted restrictions.

References

Temminck CJ 1824. Monographies de Mammalogie Tom. 1. Paris: Dufour. 60-65.. 
online pdf

Ting S and Li C 1987. The skull of Hapalodectes (?Acreodi, Mammalia), with notes on some Chinese Paleocene mesonychids. Vertebrata PalAsiatica. 25: 161–186.

Ting SY, Wang Y, Schiebout JA, Koch PL, Clyde WC, Bowen GJ and Wang Y 2004. New Early Eocene mammalian fossils from the Hengyang Basin, Hunan China. Bulletin of Carnegie Museum of Natural History 36: 291-301.

https://en.wikipedia.org/wiki/Thylacinus

https://en.wikipedia.org/wiki/Thylacinidae

https://en.wikipedia.org/wiki/Hapalodectes

Source: https://pterosaurheresies.wordpress.com/2026/10/04/new-tiny-overlooked-thylacine-ancestor-recovered-in-the-lrt/