IIRC Harryhausen was Willis O’Brien’s assistant for a few years. I’ve seen enough movies by either animator to believe (GULP) that Willis O’Brien was in some ways the more talented animator, but he was hampered by more primitive technology in the miniatures. Example: Compare the movements of the T.Rex in King Kong to the T.Rex in Valley of Gwangi. Clearly, Harryhausen’s animation was just a little more crude in subtle ways. Or at least that’s my humble opinion.
Harryhausen got out of the business at the right time, though: Clash of the Titans was both his best and best grossing film. Stop-motion animation was already obsolete and rapidly being replaced with go motion and other computerized techniques.
Harryhausen’s personal favorite was Jason and the Argonauts. I say that Seventh Voyage of Sinbad was underrated. Golden Voyage of Sinbad was okay. Sinbad and the Eye of the Tiger was a complete embarassment. Talk about fake! Ever been attacked by a stuffed sabretooth tiger toy? Yes, it looked that bad. Between Eye of the Tiger’s release and Clash of the Titans I really believed Harryhausen was washed up.
(He was, but he had one more good encore in him with Clash).
Jim Danforth did “When Dinosaurs Ruled the Earth.” I haven’t seen “When Dinosaurs Ruled the Earth” in decades. Maybe I’ll try to find it. I know it was marketed to the “cave girl porn star” set when it came out, but as a six-year old all I wanted was 'all dinosaurs all the time."