Comparing the pic here
http://bulldogbreeds.com/valleybulldog.html to your first one I'd say Clark looks more Valley bulldog than American bulldog.
I'm guessing your second pic he was jumping or something and his ears are not normally up like that? Have you a pic w/his ears in a relaxed/foward normal position? (like when you say "cookie?"
)
bulldogbreeds.com say the Valley bulldog originated as a cross btwn the english bulldog and a boxer.
A neighbour of my mum's had an American Bulldog (like Chase in
Homeward Bound) little to no wrinkling on the muzzle and they are taller and alot less stockier than the Valley, and English bulldogs.
American bulldog males range from 22-27 inches, Valley bulldog males range from 15-22 inches English bulldogs 12-14 inches