What was the biggest prehistoric cat ever?
The largest cats to have evolved are normally consideres to be the large American lion where from all the sources I've seen range from 380 KG to a stunning 500 KG meaning that by some distance they are quite large compared to any modern day Cats probably comparable to Ligers in size. The phenotype denotes that they were quite similar in appearance to modern day African lions, but just on average larger and with minimal manes similar to modern day tsavo lions, the reason their appearance is so vividly described compared to other extinct cats is due to their almost perfectly preserved fossils from the la brea tar pits in California. One particular source states that it was more closely related to Tigers than lions which I don't realy believe to be true due to the fact that the only reason for such a comparison is the skull, the Panthera atrox actually morphologicay is still more similar to Lions than tigers. When it comes to evolution the The American lion seems to have an intermediate between the lion/leopard and jaguar lineage meaning that it was a powerful cat having something of a lion- jaguar like build (pound for poumd jaguars are the strongest cats). they eventualy died out probably due to competition from smaller carnivores that required less energy to sustain their existence i.e cougars which remains the case with most of the larger mamals of north America like the giant short faced bear that was eventualy replaced by the brown bear, they were simply to big and could not be sustained in the ecosystem. other factors include hunting from paleolithic American Indians and the megafauna extinction at the end of the ice age.
The other large powerful cat from this similar time was the Smilodon populator of south America. Smilodon populators size also varies from Tiger sized to a size similar to the American lion (although the heaviest specimen is now at a more refined estimate of 400 KG than the previous thought 500 KG), although they were shorter (lions are generaly the tallest extant cats with modern day lions being taller than tigers) but more robustly built. the most popularized description of them is being bear like lions due to their imense muscular build as their main method of hunting was simply wrestling its prey to the ground so as to get a clean bite. though it had longer canines than the American lion it also had weaker jaws as the jaws of these cats were not evolved for power but rather precision unlike the pantherines sometimes known as biting cats who have a significant force behind those shorter caninnes. the main reason for this can be said to be the evolution, the large canines of smilodon meant they were fragile and thus to be effective a longer snout was required which meant the zygomatic arches of this cat were smaller thus meaning at best it only had the biting force of a third the strenghth of a modern day African lion. This is quit interesting as the saber tooths with the longest canines often had the weakest bites. But in order for those jaws to be effective the cat had immense muscular strenghth simply to just pin down the prey as most of its prey was larger than itself meaning that it was incredibly powerful and could easily be the strongest cat to have evolved.