Island proximity has nothing to do with dinosaurs building complex machines.
Why believe in seaworthy dinosaurs and not in the god Thor, if there is no evidence for either?
Fossil evidence suggests either sea-migrating dinosaurs or moving continents.
Sea-migration isn't really that far fetched. There is a chain of islands across the Bearing Straight between Russia and Alaska spread about 20 miles apart, visible to each other, which are easily swimable.
Tom raises a valid point to your observation.
Disregarding the argument concerning opposable thumbs, which by the way one of mine is not yet I am still able to function under my own brain power, James' argument can still be sound even if applied to modern day thinking and so called scientific evidence.
There is undisputed agreement amongst the modern scientific community that there is proven migration of species over short term distances across bodies of water by means of swimming or piggybacking on driftwood.
If we take Tom's observations and Jame's conjecture can we not build a simple model of creatures migrating across open bodies of water by accident and then, as all creatures do, of the learning process taking effect and accelerating.
I'm not proposing that pterodactyls built themselves aircraft carriers but it is entirely feasible, given modern understanding of, for instance, how a raptor operated and integrated with it's peers that a level of comprehension was evident that would allow for understanding and evaluation of a given situation which could lead to a conscious decision to travel across open water to seek prey.