The most efficient way to kill them are using some stegosaurus which can easily hit many ate one blow u can also use a basilisk or a bronto . However these are very good tames and and can easily kill big animals if u tame 4 or 5 of them
When in areas that have many dimorphadon remember to be careful and not to hit one by accident when fighting other creatures as you can easily be overwhelmed.your mount will not be able to save you as they deal damage directly to the rider.
I went to raid a base with 4 buddies, a rex, 3 carnos, and a bronto with a platform saddle and cannons. All we heard was a whistle and i swear about 50 of these little devil's swarmed the whole group, killing everyone in the group and one carno, the turrets shredded everything else, but the rex must have ran off and we never got a death message so its still out there in the jungle.