At the base of the Pterosauria
there was one false evolutionary start that gave us Austriadactylus (the Austrian specimen) and Raeticodactylus. Thereafter the clades kicked into full gear with the basal dichotomy, dimorphodontids (which begat anurognathids) and eudimorphodontids (which begat everything else.)
Knowing that a picture tells the story here are the players (Fig. 1):
The basic dichotomy of dimorphodontids and eudimorphodontids (Fig. 1) set the pace for the rest of pterosaur evolution. One emphasized the longer, leaner snout of a fish and tetrapod eater while the other had a taller, more fragile and ultimately wider rostrum (in anurognathids) of an insect eater.
You can see (Fig. 1) with such short fore limbs and long hind limbs, with toes under the center of balance at the shoulder glenoid (arm pit) that quadrupedal locomotion was something that would have to be invented in the future of these Triassic clades.
Yesterday’s note on Atopodentatus garnered about twice as many viewers. Let me know why all the interest because I don’t have a clue.