0.63" (1.61 cm) Aquatic Reptile (Plesiosaur?) tooth. From the Chinle Formation found in Navajo County Arizona. From the Late Triassic about 205-215 million years old.  

 This a very odd tooth. There are faint carinae with no serrations. The tooth is not straight but curved towards the top. The enamel is wrinkled. The tooth resembles plesiosaur teeth, but no plesiosaurs are known from the Chinle .