This is either a miniature thylacine, or a damn giant of a platypus…thylacines ranged from 40-70 lbs (20-30 kg) as adults (they were about the size of a small greyhound, but built more for stamina than speed), and platypuses are considered BIG if they reach 6 lbs (2.6 kg).
Roosevelt’s Thrilling Experiences in the Wilds of Africa Hunting Big Game. Marshall Everett, 1909.*
*No, this scene is not from Africa. It is from an account of another explorer later in the book, who went to Tasmania