0.5" (1.22 cm) Dinosaur tooth. From the Chinle Formation found in Navajo County Arizona. From the Late Triassic about 205-215 million years old.  

 The serrations are too small and the wrong shape for rauisuchid. The tooth is too big to be a Coelophysid. The serration shape matches dinosaur the best, the tooth is compressed also. Not much is known about the teeth of Chinle Formation dinosaurs, so I cannot say what species. Chindesaurus or Tawa are possibilities.