passage: Littlefoot 's grandfather one night tells the children a story about ` ` The Lone Dinosaur '' , a legendary longneck who once protected the Great Valley from the most ferocious sharptooth ever to live .
  A fight ensued , which led to the Sharptooth 's death .
  However , the sharptooth left ` ` The Lone Dinosaur '' with a scar slashed across his right eye .
  Soon after the battle , a huge monolith that resembled a proud sauropod , having life - sized Sharptooth teeth arranged around his neck , came out of the ground during an earthquake .
  The dinosaurs called it ` ` Saurus Rock '' .
  The legend also states that if anyone damages the monolith , bad luck would descend upon the valley .
  A few days later when the kids are playing , Littlefoot accidentally falls off a cliff .
  Just before he hits the ground , a gruff Diplodocus rescues him .
  This longneck introduces himself only as ` ` Doc '' and gives no knowledge of his history .
  Littlefoot is intrigued by this newcomer , who is scarred across one eye and displays prior knowledge of the Great Valley 's topography .
  For the preceding reasons , Littlefoot assumes that Doc is the Lone Dinosaur .
  He tells his friends this , narrating an apparently extemporaneous legend to support his assumption .
  Inspired , Cera 's infant nieces , the twins Dinah and Dana , go to Saurus Rock without anyone noticing .
  Later when the friends are playing , they notice that Dinah and Dana are missing .
  Recalling their talk of the day before , they go to Saurus Rock to find them .
query_and_answer: Who does Littlefoot think " The Lone Dinosaur " is ? || His grandfather
evidences: Littlefoot is intrigued by this newcomer , who is scarred across one eye and displays prior knowledge of the Great Valley 's topography . For the preceding reasons , Littlefoot assumes that Doc is the Lone Dinosaur . However , the sharptooth left ` ` The Lone Dinosaur '' with a scar slashed across his right eye .