How does this typically work?

[Jiyu Simul Stamus]

So soon enough I will be changing my character into a calico smilodon (known most commonly as the largest of the saber tooth cats)

My question is if the sizes used on site for these sorts of animal are the averages or if they can get up to the size of the largest fossils even if only one of that size has been found? As these two numbers are *Very* different for smilodon as the average is between two to three feet tall, with many being three or just above, but the largest one found was somewhere slightly above four feet. So can they get up to the largest proven size like a lion or such would, or can they only fit within the average?