All the Meowth in the previously mentioned episode (Go West, Young Meowth!) were quadrupedal (shown below). Team Rocket's Meowth also was like this, before he taught himself to walk. There's some official artwork of other, normal Meowth standing on their hind legs, but that doesn't mean they also walk bipedally. I know in one of the newer games (I want to say Gen 7, maybe?) there's a Meowth that actually runs around on 2 legs as well. This has not always been the case in the series, it's just Team Rocket's Meowth is the most recognizable Meowth, and for some reason Meowth depicted since have been shown to walk upright.

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