The bestiary provides separate entries for animal companions sometimes. When a character who either does not get an animal companion or already has one and you want to purchase an animal for a general purpose, do you use the main animal stats or the companion stats?
Let's say you want to purchase a mastodon as a pack animal to carry your things. Would you look at his Str 34 and he would not level up with you, correct?
Best Answer
Buying an Animal
Animals in the Animal and Animal Gear section under the Equipment header on the d20PFSRD site often link directly to their Bestiary entries. The mastodon doesn't, but the horse or pony above it and the monkey below it do. (And, no, I've no idea why the mastodon's abandoned that way.) But it is the game's way of implying those are the statistics that are used when an animal's found, liberated, manufactured, or purchased.
A more extensive list of purchasable creatures is hidden in the description of the skill Ride, and all of those creatures link to their bestiary entries, including creatures that are probably, even in high fantasy games, rarely ridden (e.g. dodos, porcupines).
The DM, of course, can rules that individual animals are special, having better statistics (like the elite array) or other abilities depending on how the DM's advanced the creature.
Only eligible classes possess creatures that gain the bonuses from being animal companions, familiars, special mounts, and the like. Normal folks just buy a capybara or a mastodon or whatever and replace the creature with something more substantial if the previous one's no longer meeting their needs.
"Yeah, But What about Abnormal Folks?"
Adventurers have more options for upgrading a purchased animal. The skill Handle Animal lets an owner train an animal to obey commands and is usually the first step in upgrading, but the right gear and spells especially can turn your otherwise normal animal into a utility belt or engine of destruction.
Ignoring horseshoes and other animal-specific items, the following magic items are useful for improving a mundane animal:
Special mention must be made of the helm of the mammoth lord, which is just awesome.
Some spells for making mundane animals more useful include...
This list ignores the myriad of spells that improve creatures' natural attacks--of which there are, like, a lot.