Here’s a fairly obscure animatronic: Arnie the Alligator from The Muppet Movie! Unlike Arnie’s other incarnations in the Muppet franchize, he’s first depicted here by a realistic-looking animatronic! You can watch him in action here.
The Muppet Movie (1979) - Bernie the Agent - YouTube
The rest of his appearances have been portrayed by a much more in-style Muppet.
Not sure what became of animatronic Arnie, but I’m assuming he’s in Jim Henson’s Creature Shop with most other props from his films/works! Here’s hoping, at least!