Quetzalcoatlus / T-rex juv.

During the Maastrichtian, in the last few million years of the Late Cretaceous, the ecosystems of Laramidia supported an exceptional diversity of terrestrial and flying reptiles. In this paleoecological context, the interaction between Quetzalcoatlus northropi —the largest known pterosaur—and juvenile Tyrannosaurus rex represents a plausible hypothesis for unconventional trophic relationships. Traditionally perceived as a scavenger or terrestrial predator of small prey, Quetzalcoatlus may have included juveniles of large theropod dinosaurs in its diet, when conditions and opportunities permitted.

Quetzalcoatlus northropi , a member of the Azhdarchidae family, reached an estimated wingspan of between 10 and 11 meters (33 and 35 ft), and a height of up to 4.5 meters (15 ft) when moving on land as a quadruped. Its cranial morphology—with a long, light, and toothless, yet structurally reinforced skull—and its extremely elongated neck gave it exceptional capabilities for visual detection and manipulation of small or medium-sized prey. Unlike other marine pterosaurs, Quetzalcoatlus inhabited inland continental environments and appears to have adopted a more terrestrial than aquatic lifestyle, behaving more as an opportunistic forager on semi-arid plains than as an exclusively aerial hunter.

For its part, Tyrannosaurus rex , one of the most studied apex predators of the Mesozoic, experienced extremely rapid growth during its youth. In its early stages, before exceeding a ton in weight, juvenile T. rex were more slender, faster, and more agile, with body proportions that differed significantly from those of adults. This intermediate growth stage, often described as the "gracile phase," represented a temporary vulnerability in the lives of these giant carnivores, especially if they were isolated or far from the protection of larger conspecifics.

The possibility of a Quetzalcoatlus preying on a juvenile Tyrannosaurus cannot be ruled out, although it would certainly be a rare and opportunistic event. A large pterosaur, with excellent vision and a powerful beak, would have been able to detect a wounded, sick, or distracted juvenile. If the T. rex weighed less than 100 kg—which is often the case during its first years of life—it would fall within the range of prey manageable by a Quetzalcoatlus . The attack would not involve a direct fight as between two adult carnivores, but rather a swift approach on the ground, a precise thrust with the beak to the neck or skull, and a rapid ingestion, partial or total.

This type of interaction may resemble the predation exercised by certain modern birds such as marabous, storks, and condors, which occasionally attack young large mammals or wounded animals. Although direct fossil evidence of this behavior is lacking, the spatial and temporal coexistence of both species, combined with a functional analysis of their morphology, suggests that such events, although exceptional, may have been part of the ecological repertoire of the Late Cretaceous.

This relationship was likely not unidirectional: as Tyrannosaurus rex reached adolescence, its size would have rapidly outgrown any plausible threat from Quetzalcoatlus , even reversing the dynamic. A fully grown juvenile T. rex could have preyed on smaller pterosaurs or competed with them for resources, making this interaction a dynamic example of changing selective pressures across the life cycle.

Approximate measurements of Quetzalcoatlus:

• 1:35 Scale Diorama Assembly Kit
• Length 198 mm
• Height 81 mm
• Width 132 mm