A large pterosaur comes through an anomaly thousands of years ago, giving rise to the legend of the Thunderbird. Throughout the years, more of these "thunderbirds" are spotted and one event records a small individual trying to abduct a boy in Illinois. When it is spotted again in Portland, Oregon, several of the ARC team examine the sightings. Connor believes it to be a pterosaur, and when they encounter it in the forest, he identifies it as a Quetzalcoatlus, having come through the same anomaly as the caenagnathid. Now they have to capture the elusive beast while still trying to keep the caenagnathid out of harm's way.
Its a little more low-slung and longer than I wanted, but since this is Primeval, 100% accuracy isn't guaranteed.