The true “pouched saber tooth” lived alongside dinosaurs
As you might have heard, the classical “marsupial saber tooth” Thylacosmilus atrox might not actually have been a predator analogous to saber toothed cats. While I’m sure this might be contested, it does make a lot of sense given how strange Thylacosmilus is compared to eutherian saber toothed predators. And a little overlooked argument is that we have an actual metatherian saber toothed predator that might be a closer analogue.
Named in 2015, Lotheridium mengi is a Cretaceous aged metatherian from China, living alongside a plethora of dinosaurs including the ornithomimid Qiupalong and an unnamed tyrannosaur. It is a member of Deltatheroida, a clade of Mesozoic metatherians specialised towards a carnivorous lifestyle that bear many convergences to placental carnivores such as carnivorans and “creodonts”, as well as non-thylacosmilid sparassodonts and dasyuromorphs. Deltatheroidans largely disappeared alongside non-avian dinosaurs in the KT event, but a clade of small insectivores managed to persist in Asia until the very end of the Paleocene.
Deltatheroidans in general are pretty underrated, being as linked above specialised carnivorous mammals that co-existed with non-avian dinosaurs. They seemingly replaced earlier carnivorous groups like eutriconodonts and symmetrodonts during the mid-Cretaceous faunal turnovers, these archaic weirdos giving in to a group that more closely resembles modern carnivorous mammals. A shame, but we forgive them because there’s unambiguous evidence of deltatheroidans preying on dinosaurs (and beloved deinonychosaurs at that).
Though not as large as the wolverine sized Nanocuris (which incidently lived in North America alongside Tyrannosaurus rex itself), Lotheridium mengi has the advantage of possessing long canines. Though the specific ecology of this animal is not explored in detail in its descriptor paper, the fact that it doesn’t differ significantly from other deltatheroidans aside from its gigantic toothers seems to reinforce that it lead a similar carnivorous lifestyle. Compared to placental saber teeth it does seem to have more robust canines, which imply some degree of functional disparity (more resistant perhaps?), but they are still blade like unlike the triangular canines of Thylacosmilus and kin. Likewise, it has none of the other unique speciations noted in the new Thylacosmilus paper: it still retains upper and lower incisors, its canine roots are not longer than those of placental saber teeth, its molar teeth remain aligned and blade-like (though no microwear exams have been perfomed), its jaw symphysis is more robust, it has non-divergent canines and its jaw musculature appears to have remained relatively similar to that of its relatives.
Overall, this informs us that Lotheridium mengi was a typical carnivorous mammal, and it seems to dismiss the notion that the degree of speciation seen in Thylacosmilus was necessary for a saber toothed predator. Indeed, since thylacosmilids were apparently not following a macropredator ecology Lotheridium mengi remains for now the “model” metatherian saber tooth.
In turn, this has some interesting implications on the evolution and ecology of saber toothed predatory mammals. For example it had previously been ascertained that a deep, short snout was a requirement, and while Lotheridium mengi’s skull was flattened it doesn’t appear to have had a much deeper profile in life.
Much work remains to be done and I dare say that there’s more to this than meets the eye, for for now I stan the little saber tooth that hunted dinosaurs.
