A nasty, nasty beast. The best thing this sub did was make me read corpsefall, which is awesome :D
I can imagine that in corpsefall, people would risk raids on one of these critters' dens (perhaps while they are out at a corpsefall) to scavenge the massive spines as building materials. Go to Comment
I like it. I've got a good image in my head, and its sticking. A bone-lion the size of an elephant is an appropriately epic mount for a evil giant antipaladin, or whatever.
However, I want to quote my Grandma in saying, "If all you've got is a big scary monster without any any weird powers, you've got to put a dress on it before you bring it to the ball," i.e. I feel like the Leonamuth would benefit from some weird lore or tactics.
Maybe you can make a fantastically deadly poison from its eyeballs. Maybe it wakes up sleeping animals by tapping them awake. Or it carries you off into the desert, gives you five minutes to run and hide before tracking you down (as long as it isn't too hungry) like a big, horrible cat playing with its food. Or they howl at the moon at night, except instead of howling it's like whalesong played backwards through Anton LaVey's skull without a pause for breath, and instead of a moon they howl towards the direction of the next corpsefall. Or else they use their mane-spines to build beautiful, deadly dens (I assume the spines are poisonous) for themselves and their mates, like bowerbirds. (Rival leonamuth are always trying to smash each other's dens.) Or how they'll stalk you with their bellies in the dust, so you can't see them sneak up on you, but their tails bob around 15' in the air like a golf flag is stalking you (My cat does that because he's an idiot.) Or how they roll around in their kills, spiking the remains on the their manes for a later snack. Go to Comment
The spines are poisonous, and banded in the same permutations of brown that mottle it's body. The spines are deadly poisonous, and if some ever finds its way to your bloodstream it will blacken your eyeballs and shatter your bones. However, the Leonamuth has no way to apply this poison intentionally: the poisonous mane mainly serves to discourage other leonamuth from jumping on its neck. (They are mostly resistant to their own poison.)
The poison also loses its efficacy after 1-3 days, and so it is impractical to store it. The only people who will bother poisoning their weapons are people who own a leonamuth. And when you own a leonamuth, you have a better ways to kill people than with a poisoned lance.
Leonamuths build elaborate dens. Their spines constantly grow and fall out. Discarded spines are carried back to its den and stuck into the ground, pointy end up. Larger, more practiced lions might even weave them together, to make something like palisade walls. Given enough time, this can resemble a (very small) labyrinth. There are rumors of a family of leonamuths that live together, and that have spent the last few centuries building a tremendous structure of woven spines. It is a honeycombed maze, and a familial den for the beasts. If anyone has ever found it, they have probably not survived to tell the story, so most disbelieve this "myth".
Leonamuth also use their spines to store leftovers, on the rare occasions when they are unable to finish a meal. Meat is gathered by rolling around in it. It is retrieved by shaking, like a wet dog.
Leonamuth spines are rarely made into permanent weapons, simply because they become brittle once they dry out. However, they have a famous and permanent usage in the Bone City, where they are used as dueling instruments. They have exactly the proper strength and flexibility to be used as dueling foils. The duels are always fatal and usually brief--one good poke with a fresh spine and you have only a few seconds left to poke your opponent before your brain turns to vinegar and your bones to sand.
Male leonamuth are very territorial. Although they will "adopt" a previous male's den if they take over the territory, they will also sabotage and destroy another male's den when given the chance. For smaller males, this is the only weapon they have against larger males.
Leonamuth will sometimes howl together, as regular as clockwork. They do not howl in response to any visible stimuli, but most sages will tell you that they howl in the direction of the next big corpsefall.