If your looking for these guys, I don't know if it's a guaranteed spawn but if you look around the rivers around the green obelisk, they seem to spawn to up to groups of three. I've tamed two from that same area, but be careful. That area has rexes, carnos, spinos, and allos, so bring something that can kill them. If you can't find any equus, just clear out the area. Also not about equus, but ovis can spawn here as well. I found two of them here in the jungle...

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