South east of the Coastal grotto, a buoy can be found. The skeleton is located under that buoy.
When diving under the buoy, the player character will find the skeleton of a T-Rex, accompanied by a human skeleton with next to it a lever-action rifle. Around the skeleton, 2 ammunition boxes and an average locked safe can be found.
In the Museum of History, there is a T-Rex on display, though pieces of it have fallen to the ground.