“Very large housecat” is bit of a misrepresentation of these awesome predators, so let’s talk a little bit about their size. Average weight ranges for foosa vary, but it’s generally thought to be between 15-26 pounds with the males being larger than the females (for cat-size context, American bred male Maine Coons tend to be around 18-19 pounds at full adult weight). Adult fossa are generally about 2-3 feet long, not counting about another two feet or so of tail, and super muscular.
This is LeeZoe, a female at the Lincoln Children’s Zoo, next to the 9x13″ cake pan containing her birthday feast.
(Photo Credit: J. Beierman)
Here’s her again in a barrel, for a different sense of perspective. Remember that as a female, she’s a good deal smaller than most of the males of her species.
(Photo Credit: K. Wilbanks)
The males, who are big even when they’re not giant, can sometimes reach incredible sizes. The next couple photos are of Isa, a 12 year old male and ambassador animal at the San Diego Safari Park, who weighs in at something like 34 pounds.
(Photo Credit: Nicki Boyd)
I just love this second photo - he’s getting a chance to watch a tamandua while on a trip around the facility. While he’d never have encountered a South American anteater in the wild, fossa frequently catch and eat animals close to their own body size, so Isa’s interest here could be more than just curiosity.
(Photo Credit: Nicki Boyd)
As the OP noted, these guys are incredible climbers. Here’s a photo from a demo done at the San Diego Safari Park to showcase their skill, which gives you a sense of how incredibly buff these guys are.
(Photo Credit: Nicki Boyd)
Fossa are amazing, and the OP did a great job of conveying that - I wanted to give you a bit of a sense of how big this species is, even if the females sometimes only weigh about as much as a large domestic cat.
The other thing I wish I could educate you more about - but would probably be censored by tumblr for - is their genitalia. The OP’s comment about having traits similar to cats and hyenas doesn’t quite encapsulate the sheer level of nightmare fuel going on there. I have two words for you: “clitoral spines.” If you want to learn more about that whole thing, click through here to an article about fossa reproductive anatomy.