They aren't cats. They aren't any specific animal at all actually.
Wikipedia has a WHOLE section on it!
"A running gag throughout the Animaniacs series is the question of what animals, if any, the Warners are meant to be modeled after. The series' other characters are cartoon representatio...ns of various animals such as mice, birds, monkeys, and squirrels, but the Warners are intentionally ambiguous. Various characters in the series question the Warners about this and refer to them as a variety of different animals, frequently "puppy children" owing to their ears and tails or sometimes Toons because of their 1930s appearance. When asked what they are, most often they state, "We're the Warner Brothers! And the Warner Sister." The Warners themselves often use this ambiguity as a source of humor; in one episode an entire musical number is devoted to guessing their species to which they declare "what we are dear Doctor-is cute!""
Those are the facts.
He is a cat.
The duration of Animaniacs is 1320.0 seconds.
There's no such thing as "Animaniacs 9"
Animaniacs was created on 1993-09-13.
Yes , 'Animaniacs' was aired on Nickelodeon in the Spring of 2001 .
Animaniacs - video game - happened in 1994.
Yes there are villain songs in the show Animaniacs.
Animaniacs - video game - was created in 1994-11.
They're not meant to be any specific kind of animal, just randomly designed creatures. However, in the episode "Chalkboard Bungle", they say that Wakko is a dog, although that just might have been a joke.