Interspecies Conflict/air battle
1) 150kg Quetzalcoatlus vs 20kg haast eagle (air battle)
2 150kg Quetzalcoatlus vs 300kg gastornis (land battle)
1) 150kg Quetzalcoatlus vs 20kg haast eagle (air battle): Quetzalcoatlus was a huge reptile with a wingspan greater than 2 car lengths and a standing height of approximately 5 meters or more. One of its more outstanding features was its long skull (over 2.5 meters long) and its sharp beak. Although likely a capable flyer, Quetzalcoatlus was chiefly a glider when it took to the air, and probably did not have the same level of maneuverability as the smaller Haast's eagle. The Haast's eagle was a huge bird of prey that commonly predated upon the moa, a huge flightless bird weighing well over 10 times as much as the eagle itself. In an aerial battle, the Haast's eagle (with a wingspan less than 1/3 of the reptile's) will be able to maneuver through the air with much greater ease, and should be able to attack repeatedly with its dangerous talons (and beak) until serious wounds are inflicted. It may take some time (as it may have taken time to dispatch a moa), but as long as the Haast's eagle stays away from the beak of the Quetzalcoatlus, it should be able to prevail. It will be somewhat difficult for the pterosaur to apply any effective offense against the quicker bird while in the air. Edge to Haast's eagle.
2) 150kg Quetzalcoatlus vs 300kg gastornis (land battle): Quetzalcoatlus was probably an active hunter of small-to-medium sized animals as well as a scavenger, and probably utilized its long beak as a spear to incapacitate prey items on occasion. It probably had very limited mobility while on the ground, but presumably could have stabbed quickly with its beak at anything that came into range. Gastornis was a heavily built bird with a powerful, thick beak and strong legs. It probably could have delivered a strong bite with its beak and strong kicks with its legs in a combat situation. In this battle, Quetzalcoatlus will stand close to 2 1/2 times as tall as Gastornis, and will have a huge "reach" advantage with its long beak and great height. Although Gastornis will be capable of injuring Quetzalcoatlus at close quarters, it will be in danger of getting speared before it gets close enough to use its kicks and bite with any great effect. Gastornis will have better lateral quickness, but that asset won't be enough to consistently keep it out of harm's way if it chooses to attack instead of playing "keep away". Assuming Quetzalcoatlus could indeed employ its weaponry on the ground as described (making quick, far-reaching stabs with its long beak), it would likely be able to hold its own against many animals heavier than itself. Edge to Quetzalcoatlus.