User blog comment:Gekkou30/The T-Rex Roar/@comment-1791057-20130815025634

The females in the first and second movie used a baby elephant, tiger, alligator, whale, and dog mixture. For the male (at least in TLW) Gary Rydstrom and the SFX team sourced from different animals to make the male Tyrannosaurus roar deeper than the females'. Sounds for the male included, pigs and some other "weird Costa Rican mammals that [they] didn't even know what they are." Instead of using the baby elephant rumbles and squeaks that was the base for the female T. rex bellow (and continued to be the base for the female in TLW), the male's roars are made up of all "baby elephant-like" sound recordings that were twisted to mimic the sounds of the females roar. However, the rest of the roars that were mixed into the T. rex vocalizations were the same for both genders.