Not sure how this mistake was overlooked for fifty years.
But other traditional mistakes have survived and thrived far longer. C’est la vie paleo!
Barbourofelis fricki (Schultz, Schultz and Martin 1970; Middle to Late Miocene, 13-7mya) was traditionally considered a placental member of the Carnivora and a big cat (= Feliformia). Here it nests with Thylacosmilus (Fig. 2) as a saber-toothed marsupial. Distinct from Thylacosmilus, four procumbent tooth alveoli are present on a broad, transverse premaxilla. Three large molars have shearing surfaces, as in big cats, rather than typical grinding surfaces. The premolars are tiny. The sabers are slender, as in Thylacosmilus. The orbit is enclosed, as in Thylacosmilus. The dentary has saber flanges (not scored in the LRT), as in Thylacosmilus. The mandible (= dentary) must hyper extend in order to clear the sabers.
Marsupial relatives of Thylacosmilus and Barbourofelis include
Vincelestes from the Early Cretaceous, which also has large, semi-saber canines, both uppers and lowers. So saber-toothed therians held their own against dinosaur predators throughout the Cretaceous. This gave plenty of time for Thylacosmilus and Barbourofelis to diverge in traits and geography, yet so much remained the same.
Moving Barbourofelis to Panthera
(the placental, Carnivora, Feliformia, lion) in the large reptile tree (1973+ taxa) adds 32 steps.
According to Wikipedia/Thylacosmilidae,
“The family’s most notable feature are the elongated, laterally flattened fangs, which is a remarkable evolutionary convergence with other saber-toothed mammals like Barbourofelis and Smilodon.”
By contrast, the LRT nests Barbourofelis with Thylacosmilus. Smilodon came along later by convergence.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
Schultz CB, Schultz MR and Martin LD 1970. A New Tribe of Saber-toothed Cats (Barbourofelini) from the Pliocene of North America. Bulletin of the University of Nebraska State Museum. 9 (1).