What happens if I cast decompose corpse on a shark. Most of their "bones" are made up of cartilage.
As you might guess, I'm playing a necromancer in Skull and Shackles.
Just the corpse... saving them for later.
If the cartilage is what mostly makes up the "skeleton" of the shark, then you will have a Skeleton.
A soft, floppy skeleton! Maybe give it a bonus against grapples? You know, from all of those octopus animal companions...
I'd say no; a shark does not have a skeletal system, so it decomposes to nothing but jaws and teeth when a decay spell is used on it and cannot be brought back as a skeleton. A shark's skeleton is comparable to the human nose and ear, which all undead artwork in Pathfinder shows have decayed away.
With no hard rules to go by, that'd be my common-sense ruling. Nothing wrong with shark zombies though ;-)
Even better- just animate the jaws to chatter around on the ground like wind-up teeth. Except then it brutally maims you because it's still a shark's jaws. Shark jaws are bigger than a human's, but they aren't that big, so I'd say they'd be a tiny undead. It couldn't be more than 1HD- think of how many you could control! An army of chattering shark teeth!
Or a swarm of shark jaws...
I'm mostly using decompose corpse as a way of cleanly storing and cataloging my various corpse "treasure" to use as disposable undead minions as needed. A restore corpse spell should restore the corpse to that "just dead" feeling, so I can make them into fast zombies.
I agree with decomposing to just jaws (but are even those made of bones?), and think that a proper use for them is to make severed heads of some kind. Depending on shark size, I think it'd either be exactly like RAW but with bite instead of slam, or an advanced version of small size with like 2-3 HD.