Possible Clues:

• T. rex, for example
• Pet for Fred, Wilma and Pebbles
• Ankylosaurus or iguanodon, informally
• Stegosaurus or triceratops, for short
• Prehistoric beast, in brief
• 'Jurassic Park' creature
• Triceratops, e.g., informally
• Source of a museum skeleton, for short
• Natural history museum display, for short
• Critter on some pj's