The Quetzalcoatlus is a pterosaur, and perhaps the largest known. They appear in the third film chasing Buck, Crash and Eddie while they were flying to save Sid in Lava Falls. They almost caught them but Buck piloted Roger to Lava Falls. He pulled up sharply in front of a lava waterfall, but the Quetzalcoatlus' were unable to pull up fast enough and they plunged straight into the lava.
Just like other pterosaurs, they were not a dinosaur.