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Quetzalcoatlus - the largest pterosaur 

Reconstructions by Mark Witton. 

When: Late Cretaceous (68-65 million years ago)

Where: North America

What: Quetzalcoatlus is a gigantic pterosaur. Just how gigantic it was has been the subject of some debate, as no 100% complete specimen has been found. While the first estimates put its wingspan at up to 50 feet (16 meters) this has been reduced to 36 feet (11 meters) in the latest studies. The reason for this disparity is due to allometry - the physical properties of bones require that as an animal gets larger its skeletal structure is not just that of a smaller animal made larger. Thus the wing bones of Quetzalcoatlus were relatively thicker than that of a smaller species, and while this was taken into account in the first estimates, it took a better understanding of pterosaur evolution in general for a refined estimate to be generated. 

This large size brings with it another debate: could Quetzalcoatlus fly? The answer is yes, this pterosaur sailed over prehistoric Texas. A big mystery was how Quetzalcoatlus could take off, and recent work by functional morphologists has provided a solution to this puzzle. Pterosaurs differed from all other flying vertebrates in that they retained the majority of the digits on their hand outside of the wing itself; this not only allowed these fingers to be used to manipulate their environment, but was critical for terrestrial locomotion. Quetzalcoatlus was quadrupedal on the ground, like all other pterosaurs, but it had a specially developed system of ligaments and tendons in its wrist joint that allowed it to ‘spring’ up and take flight.  This can be seen in this video.  

Another, more minor, debate is what did Quetzalcoatlus eat? Most pterosaurs are closely associated with large bodies of water and have a fish based diet - but all Quetzalcoatlus remains have been found hundres of miles from ancient shorelines. This, combined with morphology of the skull, has lead to the conclusion that these giants instead fed on smaller vertebrate that they would capture with their large beaks, such as the baby sauropod not having a good day in one of the reconstructions above.