Actually, I have to add (After that book cover reminded me) that the mini-terrordactyl puppets used in episode one of IOTD were pretty damn good, almost Hitchcock/Birds levels of scary.

(Ooh look, I accidentaly found the photo that cover was based on!)

Maybe they were constructed by different guys and they were of course photographed by the main unit in camera, unlike the big Dinosaurs, who were shot by the model unit. Plus it helps when you've got a great actor like Pertwee reacting to them live on set (A lesson certain Directors with a penchant for CGI could use).