The phylogenetic scattering of the traditional clade ‘Sparassodonta’ in the LRT

According to Wikipedia – Sparassodonta
(Early Paleocene to Late Pliocene, 65-3mya, Ameghino 1894) “is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now thought to be a separate side branch that split before the last common ancestor of all modern marsupials.”

See online cladogram from Suarez et al 2105.

Click here for a geographic distribution of traditional sparassodonts in the LRT compared to interwoven sister taxa not from South America. Scroll down below the Suarez et al cladogram to see the LRT subset.

“Almost all sparassodonts have an exceptionally shortened snout—most especially thylacosmylids.”

Exception: Lycopsis longirostrus, does not have a short rostrum.

“They exhibit marked postorbital constriction.

Not exclusively. Many examples are exceptions and vice versa.

They have an expanded occipital bone with a well defined nuchal crest.”

Again, not exclusively.

“Sparassodonts have highly reduced epipubic bones (pelvic bones which support the pouch), to the point that early analysis could not even find evidence for them.

I’m still looking for one example of prepubes, even in Thylacosmilus.
Middle Eocene Callistoe is known from a nearly complete skeleton and skull, but the missing pelvic portion would have included the prepubes, if present.

As with thylacines, it is very likely that they possessed long cartilaginous elements instead.”

That would be by convergence, if so, according to the LRT.

Forasiepi and MacPhee 2019
cited earlier authors in defining Sparassodonta as “the group that includes the common ancestor of Patene and all its descendents.”

Unfortunately, Patene is known from isolated teeth and jaws.

Although Thylacosmilus is a purported marsupial,
Forasiepi and MacPhee 2019 reported, “Thylacosmilus possessed a U-shaped ectotympanic that was evidently situated on the medial margin of the external acoustic meatus. The bulla itself is exclusively composed of the tympanic process of the exoccipital and rostral and caudal tympanic processes of the squamosal. Contrary to previous reports, neither the alisphenoid nor the petrosal participate in the actual tympanic floor, although they do contribute to the roof. In these regards Thylacosmilus is distinctly different from other borhyaenoids, in which the tympanic floor was largely membranous (e.g., Borhyaena) and lacked an enlarged ectotympanic (e.g., Paraborhyaena).”

“Most sparassodonts can be viewed as specialized hypercarnivores with only 10% of species qualifying as omnivores or mesocarnivores.”

In the LRT
the ectotympanic appears in placental grade taxa.

The two-part alisphenoid + petrosal are traditional marsupial traits.

In the LRT Thylacosmilus nests not far from a placental taxon, Melursus.
See below.

On this topic, a new web page was created
for a subset of the LRT focusing on early Mammalia, their geographic distribution across continents and the scattering of traditional sparassodonts. So, at present, this traditional clade is not recovered as a monophyletic clade. Furthermore, scattered creodont clade members include continents other than South America.

The phylogenetic scattering of early mammals across so many continents speaks to their mobility in the Mesozoic to cross continents (prior to continental drift).

A surprise appearance in the clade Creodonta
is the South American sloth bear, Melursus. If valid, this marks the whole clade as placental. All other clade members are extinct, so without this single example their reproductive strategy could not be ascertained.

Sorry about that.
Sparassodonta joins a long list of other clades that were not recovered by the LRT. A competing cladogram with a similar taxon list that joins traditional sparassodonts is now needed to invalidate = improve the LRT.

Cladograms of sufficient taxon size solve many problems.

References
Ameghino, F. 1894. Enumeration synoptique des especes de mammiferes fossiles des formations eocenes de Patagonie. Boletın de la Academia Nacional en Ciencias, Cordoba 13:259–452.
Prevosti FJ and Forasiepi AM 2018. Evolution of South American Mammalian Predators during the Cenozoic: Paleobiogeographic and Paleoenvironmental Contingencies. Ameghiniana 55(3):363-364.
Suarez C et al (3 co-authors) 2015. Insights into the Neotropics prior to the Great American Biotic Interchange: new evidence of mammalian predators from the Miocene of Northern Colombia. Journal of Vertebrate Paleontology. 36 (1) e1029581.

wiki/Sparassodonta
reptileevolution.com/sparassodonta

 

Source: https://pterosaurheresies.wordpress.com/2026/03/31/the-phylogenetic-scattering-of-the-traditional-clade-sparassodonta-in-the-lrt/