To get this achievement you need to be on the Multiplayer map, Epicenter. This map is in the Aftermath expansion. Once you're on this map, go to where the C flag is located in Conquest. Once here, look for a pipe that you can crawl in. Once found, crawl through the pipe til you see this little dinosaur and shortly after discovering the dinosaur, an achievement unlock will pop up.
Thanks for posting! I had been walking around on scavenger mode looking for it until you said it was conquest. :wacko: