Sabretoothed tiger? Wrong... This animal has more in common with a kangaroo than any felid.
Thylacosmilus atrox was a large sabretoothed sparassodont (a metatherian that shares common ancestry with marsupials) found throughout Miocene S. America. The enlarged canines are an example of convergent evolution...the appearance of similar traits in independent lineages.
What makes Thylacosmilus teeth so unusual is that they are ever-growing. The tooth-roots, extend all the way above the orbits, essentially functioning like rodent incisor roots, providing constant fodder for ever-erupting teeth. A clear advantage, in that the frailty of their teeth would be compensated with regeneration.
The histology of the teeth is more consistent with that of tusks, with very little enamel coating and unlike the more heavily enameled teeth of big cats, this makes sense given the continuous regrowth of teeth (enamel's hard crystalline structure doesn't lend well to regrowth). This profile is consistent with exposed teeth, which is interesting given the recent debate over lip covering in sabretoothed cats, whose enameled teeth would have instead been better suited to a sheathed environment.
Thylacosmilid lower jaws, however, provide the best outright evidence for sheathing among all saber-toothed predators. Most developed lower jaw structures - flanges, extensions that in life would have served as sheaths for the canines. Thylacosmilus is by far the most extreme example in possessing long flanges that are almost a third of the whole skull’s depth. In most restorations, these flanges are depicted as lip-less, giving way to the canines.
However, virtually all mammals have lips, and in metatherians suckling is extremely important in early stages of life, as joeys are attached to their mother’s nipples. If marsupials are suspected of less facial diversity than placentals because of this, what chance did the closely-related-but-still-pouched sparassodonts have? Requiring some seriously radical facio-muscular changes in their development...conclusion: lips
#skull #evolution #fossil #nature #prehistoric #mammal #sabretooth #naturalhistory #marsupial #paleontology #naturalist #animal