If we never found them in close proximity, we would rather doubt that they were related On the other hand, if we were to find them living in the same place that would support the pterosaur to bird theory.
Well they have been found living in the same place:
"The world's first pterosaur tracks from Japan, documented in a new study, suggest these Dinosaur-Age flying reptiles not only coexisted with birds, but that the two groups also hung out together when they weren't soaring the Cretaceous skies.
A lone siltstone slab contains the fossilized footprints, made by pterosaurs, birds and amphibians. It provides a literal slice of what prehistoric life was like in Japan around 127 million years ago.
"I think that a group of small pterosaurs was feeding together near a pond or near a lake," lead author Yuong-Nam Lee told Discovery News, adding "there are lots of feeding beak marks."
For the latest study, accepted for publication in the journal Cretaceous Research, Lee and his colleagues focused on the pterosaur tracks. The scientists identified a total of 64 imprints made by five to six individuals that "show a clear quadrupedal gait pattern" with feet bearing curved "hook-like sharp" claws.
"The high density of the tracks suggest gregarious behavior, but the random orientation of the trackways does not show that they were moving in the same direction as a herd," Lee said.
He and his team instead think the pterosaurs and birds randomly gathered to feed. The eating marks consist of "small round depressions on the slab," possibly where the animals repeatedly pecked away for food."