Elephants are classified as prey animals because they have a resource-analogue. Rams are included because I didn't want Sheep resources to be left out. I can justify Rams as barely Strength 1, but I can't justify anything smaller, so Fur is going to have to be the odd resource out.
I also don't want to have Hunter units, and I don't want to make prey defend-only; I don't want to mess around with the Unit AI routines (all animals use UNITAI_ANIMAL). What I'm looking for here is to provide enough choices to make this mechanic interesting without so many additional parts that it becomes more like a tumor. All told, there are 23 new units (6 wild prey animals, 6 captured prey animals, 11 captured predator animals; but only the prey need new art definitions, which is the biggest impact in computing resources), 5 buildings (3 Myths, Menagerie, Zoo), and the mission/outcome system defining 2 missions (butcher and herd) and 6 outcomes (hunting kill, subdue, herd, and the three different butcher results). I think this
As far as using Captured Animals to sweep for resources; the game checks to make sure the resource is legal on the chosen plot before it allows the plant mission. For example, you can't plant Deer on a plot without Forest or Jungle. So you can only sweep with a given animal for the tiles that are already legal. Bare Desert cannot be checked; the only animal resource that will plant there is Ivory, and as far as I can tell, only if it's a Flood Plain Desert. You would need several different prey animals to sweep even most terrain, and you'll certainly never get 100% coverage.
I also don't want to have Hunter units, and I don't want to make prey defend-only; I don't want to mess around with the Unit AI routines (all animals use UNITAI_ANIMAL). What I'm looking for here is to provide enough choices to make this mechanic interesting without so many additional parts that it becomes more like a tumor. All told, there are 23 new units (6 wild prey animals, 6 captured prey animals, 11 captured predator animals; but only the prey need new art definitions, which is the biggest impact in computing resources), 5 buildings (3 Myths, Menagerie, Zoo), and the mission/outcome system defining 2 missions (butcher and herd) and 6 outcomes (hunting kill, subdue, herd, and the three different butcher results). I think this
As far as using Captured Animals to sweep for resources; the game checks to make sure the resource is legal on the chosen plot before it allows the plant mission. For example, you can't plant Deer on a plot without Forest or Jungle. So you can only sweep with a given animal for the tiles that are already legal. Bare Desert cannot be checked; the only animal resource that will plant there is Ivory, and as far as I can tell, only if it's a Flood Plain Desert. You would need several different prey animals to sweep even most terrain, and you'll certainly never get 100% coverage.