The DINO.3O is an unused model file included in the demo version (1.02) of Chasm: The Rift Wiki.
Portrayed as a green mutant dinosaur, "DINO.3O" can be found in a subfolder of demo version 1.02 along with "3OVIEW.EXE", "SCELET.3O", and "MONSTERS.TXT".
"MONSTERS.TXT" reads "Here are some of characters which we are not include in demo. To view character type: 3oview scelet.3o to view Sceleton, 3oview dino.3o to view Dino". When this program is run and the model is loaded, it displays the model rotating on its axis.
The ".3O" model format was likely changed throughout the development process as no models besides the two included in this folder can be viewed with "3OVIEW.EXE".