“Four possible skulls are known for Apatosaurus. The Carnegie's CM11162, two in the Glenrock, WY paleo museum, and a possible fourth in a museum in Cincinnati. All show a strong family resemblance to Diplodocus, the most obvious differences being in the length of the skull and the width of the muzzle.
“Since the Carnegie's was known to be distorted but to an unknown degree, I elected to base the model's skull on the only other known skull at that time, WDIS099 (below). It was discovered in Wyoming in Como Bluff's Nail Quarry in 1995 and thought to be from A. excelsus. It was found disarticulated and was prepped and assembled by Melissa Connely, under the direction of Bob Bakker. The internal structure of WDIS099 was badly distorted, especially the pterygoid bone. Melissa sent a sketch of how they more probably should have looked, which I incorporated into the model (see sketches below). Its right side was essentially missing. A cast of the skull shows an iron rod pulling the external structure into its more correct configuration. Connely reported that the nares were missing and that the orbit was somewhat depressed. I added the nares, based upon Diplodocus, but elected not to significantly raise the ridge over the eye, not knowing for sure how much. However, the subsequent discovery of another skull in Wyoming appears to confirm that the orbit was very arched, similar to Diplodocus (see Skull #3 below).”