Sculptress Virginia May is seen making a clay model of a tyrannosaurus rex, which is animated using stop motion, and then fights a stop-motion triceratops. Although Miss May's only known relationship with the movies is this particular short, her contemporary, Willis O'Brien and his student Ray Harryhausen certainly made the field a lively one until computer animation caught up in the 1990s -- and arguably their artistry is still unsurpassed.
Unfortunately the movie Pathé Review: Monsters of the Past is not yet available on HBO Max.