Humpty Dumpty Circus (lost animated short; 1908)
From The Lost Media Wiki
The Humpty Dumpty Circus was a stop-motion short from 1898 that was directed by J. Stuart Blackton and produced by Albert E. Smith, who also used his daughter's dolls as props.
It is considered to be the first (known) stop-motion short ever made but has unfortunately been lost to time with no footage available, with only a few stills known to remain.
Considering how old it is combined with the lack of film preservation around the time, it's highly unlikely that it will ever be found.
Gallery
Stills provided by LMW user CloudStrifeX15Rain