266272
When Marsh named it , he thought it was a jaw with a tooth from a Mesozoic pig , but it was soon shown that the specimen was an eroded vertebra , from a dinosaur possibly from the Morrison Formation of the Rocky Mountain region ( the provenance data was unclear ) .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None