 A. fragilis is the type species and was named by Marsh in 1877 . It is known from the remains of at least sixty individuals , all found in the Kimmeridgian – Tithonian Upper Jurassic @-@ age Morrison Formation of the United States , spread across the states of Colorado , Montana , New Mexico , Oklahoma , South Dakota , Utah , and Wyoming . Details of the humerus ( upper arm ) of A. fragilis have been used as diagnostic among Morrison theropods , but the discovery of " A. jimmadseni " indicates that this will no longer be the case at the species level . 
 A. fragilis <a href='drop_aux' title='1'><mark>is</mark></a>the type species and was named by Marsh in 1877 . It is known from the remains of at least sixty individuals , all found in the Kimmeridgian – Tithonian Upper Jurassic @-@ age Morrison Formation of the United States , spread across the states of Colorado , Montana , New Mexico , Oklahoma , South Dakota , Utah , and Wyoming . Details of the humerus ( upper arm ) of A. fragilis <a href='been_done' title='2'><mark>have</mark></a> been used as diagnostic among Morrison theropods , but the discovery of " A. jimmadseni " <a href='uninflect' title='3'><mark>indicates</mark></a> that this will no longer be the case at the species level . 
A. fragilis the type species and was named by Marsh in 1877 . It is known from da remains of at least sixty individuals , all found in the Kimmeridgian – Tithonian Upper Jurassic @-@ age Morrison Formation of the United States , spread across the states of Colorado , Montana , New Mexico , Oklahoma , South Dakota , Utah , and Wyoming . Details of the humerus ( upper arm ) of A. fragilis done been used as diagnostic among Morrison theropods , but tdadiscovery of " A. jimmadseni " indicate dat this will no longer b the case at thdapecies level .