In the Triassic the Rhamphorhynchoidea Family were the first and they were sparrow sized and up. They went extinct at the Jurassic Cretaceous extinction event. The Pterodactyloidea arose during the upper Jurassic and were generally larger but there are examples of smaller forms. These animals are reptiles and it is a feature of reptiles to grow throughout their life but the evolutionary trend is definitely to larger species until their demise. All I can say is the cliche that there must have been an evolutionary advantage to do so.

In my imagination seeing Quetzalcoatlus with a thirty five foot wingspan fly close over my head would make me duck.

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily available to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

"Quaerendo inventis"