A new species of mastodon that lived during the Pleistocene period has been identified from fossil found in California and Idaho. The Pacific mastodon (Mammut pacificus), holotype skull and tusks; a skull in: (A) dorsal, (B) ventral, (C) left lateral, (D) right lateral, (E) posterior, (F) distal end of left tusk (I1), lateral, and (G) right tusk (I1), lateral view; (A-E) images of a resin cast of the holotype skull on exhibit at the Western Science...