Zaurus is a Reptile-type enemy that can be found in the Omega Ruins. You need to capture five of each Reptile-type enemy in order to unlock Ornitholestes in the Species Conquest section of the Monster Arena.
Defeating Zaurus is very easy to do. One swing from Tidus’ Longsword or Wakka’s Blitzball should do the trick.
|“Immune to sensors.”
|“Immune to scans.”
They can be found anywhere in the Omega Ruins. They tend to be more abundant near and around the Save Sphere at the entrance.