u/GGain9

my theory is that Thylacosmilus hunted prey that was much, much larger than itself(like a weasel). Thylacosmilus immediately stands out from all sabretooths, having by far the most extreme sabres - they have a triangular cross section, and were very thin and blade-like(even compared to other sabretooths.) Thylacosmilus may have had among the most fragile teeth of any sabretooth. they were also proportionally among the the longest and most deep rooted. these sabres were so extreme, that their eyes were almost side facing - if Thylacosmilus was an ordinary sabretooth, all of these adaptations would be unnecessary - longer, thinner teeth means higher risk of breakage when subjected to random directional forces, and even a slightly higher risk is too much to be evolutionarily stable unless if there is a less risky alternative. there is no real benefit to having longer, thinner canines if Thylacosmilus was regularly eating similar sized prey - shorter, stronger teeth can still pierce just as deep and still lacerate the cartoid and windpipe with a lesser risk of breakage. semi-side facing eyes are a big disadvantage when hunting agile 100-200kg ungulates. tracking prey is important for predators, but with a blind spot and semi side facing eyes, this would become difficult. to add to this, thylacosmilids also had bony flanges, which are metabolically costly and unnessecary if it used a smilodon style hunting method(smilodon did not have bony flanges). it all seems like its maladapted to the smilodon niche now picture a Thylacosmilus hunting a one ton megafaunal animal, and all of its extreme adaptations make sense - it doesn't need excellent vision to track a huge lumbering Toxodon. giant animals often have thicker hides, so having thinner canines allows smoother puncturing. longer canines might be more fragile, but they also pierce deeper and inflict more damage, which is exactly what you need to subdue giant prey with thicker layers of muscle and skin. large animals often have poorer senses, so a Thylacosmilus wouldnt have to be as stealthy as it would for a fast, alert Theosodon. another feature that Thylacosmilus has is the lack of bone tolerance. this means that more food has to be found, as it cannot derive nutrients from the marrow as a more generalised carnivore could - if hunting smaller prey every bit of energy should be consumed, because each hunt puts the predator at risk and expends lots of energy. for a pedator that eats prey much larger than itself, it can be pickier(and doesnt have to compromise its sabres) because much more soft flesh is available in a 1.1 tonne toxodon than in an 100kg adinotherium. so, how could it hunt prey that is bigger than itself? my main theory is that it would latch on(like a weasel) - its body is very well suited to this - it has semi opposable thumbs on both its hind legs and front legs(allowing greater grip). its body is very low slung which makes them significantly harder to shake off(due to the low centre of gravity) and improves ballance. the stiff back acts like an anchor. plantigrade feet increase stability giant megafauna have slow reactions, poor reflexes and have many blind spots - attacking from behind or from other angles could give an easily accessible window of opportunity. after latching on, the Thylacosmilus will repeatedly drive its canines into the flesh of the prey - the beauty is that the location doesn't particularly matter- a deep bite can cause serious shock and blood loss anywhere, because the canines are 7 inches long(respectable length if you ask me). if this is true, then it does not have to wrestle prey to the ground and target a particular area of the neck(as smilodon did) which is super risky, especially for the canines, which are literally even more fragile inThylacosmilus. large animals tire much more quickly than smaller ones, so it wouldn't have to latch on for that long before blood loss and shock would weaken it. when prey is weakened, more directed bites can happen. lastly i would like to explore a case study of extreme macropredation in nature. a weasel and a rabbit. rabbits are about 10 times heavier than a typical least weasel- a typical least weasel can max out at around 13km/h for short distances - rabbits can bound around 50km/h for longer distances so can easily out pace a weasel(thylacosmilus was probably faster than its prey). rabbits have very acute senses, with almost 360 vision and excellent hearing, they can detect threats much better than a typical megafaunal herbivore. rabbits are very agile and can bound in a zigzag motion to evade predator, but no megafaunal animal can do this to the same extent. note that weasels probably have much higher metabolisms than thylacosmilus, because weasels are much smaller and have a higher eutherian metabolism - this means that thylacosmilus would not have to employ this risky tactic as often as a weasel would. this doesnt prove the theory, but does show that the "persistence latching" strategy might actually scale, well, and behaviours like this arent out of the question. also, to clarify, i am not stating that thlacosmilus couldnt hunt similar sized prey, I'm suggesting that it may have been able to regularly subdue and consume prey that was several times larger than itself. still this is just a theory and needs more evidence and actual biomechanical studies to prove, and I will remain open minded to your thoughts - please ask any questions/objections you like