One of the first beasts that I wanted to introduce to my Sword & Planet bestiary is the kandor, a creature that has been domesticated by the sentient races to assist with working and hunting, as well as provide general companionship. The monster entry follows:
The kandor is a common creature that has been domesticated by the sentient races to assist with working, herding, hunting and protection, as well as providing general companionship. The kandor can be found in both pet and feral varieties, and are territorial pack hunters in the wild. Well-muscled, the kandor is a vicious predator with six legs, a dog-like body and a rat-like head, standing about four feet tall at the shoulder. The kandor's coat covers most of its body (save for the inside of its large circular ears and its long whip-like tail), with a color that varies from white through grays to black, and browns that range from light (tan) to dark ("red" or "chocolate") in a wide variation of patterns. The kandor is a very social creature, using hisses, barks and squeaks as well as body language to express a wide range of information to its packmates and/or owners.
Kandor: AC 6 ; HD 4; Atk: 1 bite (1d6); ST: 13; SP: None; MV: 18; CL/XP: 4/120.
In essence, the kandor are simply osquip on a larger scale, but should prove to be pretty fun as a replacement for dogs or wolves in a Planetary Romance setting. Just imagine a giant wolf-rat coiled beside its master when the party encounters a lone woodsman in their travels, or a pack of these predators tearing through the underbrush chasing them down as they flee from an enemy's stronghold. If your players are uncomfortable with rats, feel free to play up that aspect of their appearance. After creatures get to be of a certain size, a large group of them is no longer considered a swarm; instead, we tend to call such a group a pack. Despite that, though, you can describe their charge as having a swarm-like quality about it, particularly if the PCs observe them attacking a much larger creature such as a dinosaur.
Hope This Helps,