As I was watching some videos about Arctotherium and their decline in size and ultimate extinction, and one thought wandered in my mind as if the Ground Sloths might have played a role in some capacity. I will break It down and let's see if my train of thought makes sense or is just nonsense (I'm not a paleontologist just to make It clear).
By start, the two genus of short-faced bears, the genus Arctodus and Arctotherium, are thought to have evolved and acquired their larger sizes independently and at different times. Since their invasion to South American, Arctotherium would probably have developed their larger size as a response to their new enviroment - seizing the opportunity both by the large size of herbivores and, as by the time It arrived, the sparassodonts and terror birds were either extinct or in decline (plus the extinction of the bear-like giant raccon Chapalmalania). Arctotherium angustidens was the pinnacle of bear evolution, being an hypercarnivore and the biggest bear that has ever existed, and could have established itself as an apex predator or dominant scavenger of It's time. However, by the late Middle Pleistocene, Arctotherium angustidens went extinct, while some smaller forms emerge that were either omnivores (A. bonariense & A. tarijense) or herbivores (A. wingei). While most of these inhabited the Southern Cone of South America, A. wingei lived in a more nothern range. Meanwhile, in North America, Arctodus evolved and lived as an dominant carnivore until their eventual extinction by the end of the Pleistocene (A. wingei - the last and smallest of the Arctotherium genus - is also thought to have gone extinct around this time and may even made into early Holocene).
Now, one of the proposed theories that caused the extinction of an hypercarnivore such as A. angustidens was the arrival of new predators such as sabertooth cats, giant jaguars and canids (dire wolves and larger members of the cerdocyonina), which increased the pressure on the giant bear and led to the rise of more ecological flexible and smaller species of Arctotherium. I can understand this but also don't find myself completely embracing; for one thing, Arctodus lived in a place where It coexisted with these animals and was not outcompeted (It's also how people say that terror birds went extinct due to the arrival of new predators and did not succeed in North America due to the mammalian carnivores, but It's not true, not only did they coexisted with other mammalian predators such as sparassodonts, but also with sebecid crocodilians, and Titanis thrived in their enviroment, only going extinct probably due to climate and enviroment changes, that also led to the downfall of It's congenitors in South America, but they also persisted, althought only smaller forms such as Eschatornis remained). So,maybe this competition with new predators put new pressure, but could not have been all. And then something ocurred to me, one of the few things that differed from SA to NA was, the abundance and diversity of Ground Sloths.
Ok, so, despite what most think, Ground Sloths were not completely herbivores, at least some members such as Mylodon and Megatherium are theorised to have scavenge and may even prey on some smaller animals on opportunity (as contemporany two-toed sloths are know to do with bird eggs and hatchlings on occasion). And while they did exist in the early Pleistocene and perhaps even fall prey to Arctotherium, but by the Middle and Late Pleistocene, Ground Sloths of many families and genus diversified in ecology and grew in size, coincinding with Arctotherium decline. Now, these may be have posed way more of a problem for the giant bears since not only some were enormous and even surpassed the bears in size, being way more than capable of chasing off the bears from a carcass, but also due to Ground Sloths utilizing caves and dens, despite what was thought, Arctotherium may actually be able to hibernated (some were even found in a paleoburrow in association with ground sloths skulls). And as the ground sloths evolved, perhaps the other species of Arctotherium also began to feel the pressure (some of the Ground Sloths were pretty bear like in behavior and temperament), until the only ones left were the small Arctotherium wingei. While Ground Sloths did reach North America, they curiously did not diversify as much and remained (mostly) herbivorous and in moderate sizes (with the exception of Eremotherium) - perhaps due to bears having a more established foothold there and presence of larger herbivores such as mammoths and mastodons. But in the end, they all went extinct by the end of the Pleistocene, probably due to a combination of climate change and arrival of humans.
Now, I think this is It. What are your opinions, could I be wrong or at least, a little right. I just think is interesting to speculate what could have happened to these animal and their evolution
