This is a rare sound effect that debuted in the 1952 Western film The Lion and the Horse. However, it is mostly known for being used for the Rhedosaurus in The Beast from 20,000 Fathoms, which came out a year later. Links: https://www.youtube.com/watch?v=0xoq0nqzdfY https://soundeffects.fandom.com/wiki/Rhedosaurus_Roar#Audio_Samples