Reptisaurus

Well There is a cgi monster which varies in size from shot to shot, it has no motivation for just killing everyone it encounters (not hungry, not scared, not territorial) although the characters are so bland that death is a sweet release for them.

Honestly, I was a huge fan of the original comic (Charleton Comics give you more!) back in the early '60's and the producers using the name is why I watched it. The credits claim this was based on the comic - it wasn't, it was just a misuse of the name.