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Pterosaurs, a lineage of Mesozoic flying archosaurs, include the largest flying animals ever known. Quetzalcoatlus nortropi a Late Cretaceous representative, had a wingspan of over 10 m and likely weighed more than 200 kg. It presents a combination of features (large head, massive wingspan, shoulder height equivalent to an extant giraYe) that has led to ecological interpretations of it as a major predator in the North American Maastrichtian Biome, perhaps second to only Tyrannosaurus rex. Here we examine the probability of that from an energetics perspective. Despite the great wingspan of Quetzalcoatlus, the body length (gleno- acetabular distance) is relatively small (~500 mm) and a volume of ~1.5 times that of an average sized human male. When factoring in lung volume this restricted the gut capacity and thus prey size. We estimate, for a 200- 250 kg adult, a maximum prey size of 5-7 kg. We then examined if this would be enough to sustain an adult Quetzalcoatlus and based on extant mammalian and avian field metabolic rates (FMR). We suggest that a daily food requirement would be around 3.5-5 kg per day using FMR. This suggests that such large creatures would be feeding on either very small prey items or could scavenge leftovers well after the larger theropods had secured their fill. In addition, take oY and flapping flight would be so extremely costly at such a large size, as demonstrated by the fact that in extant birds this value is often 20 times basal metabolic rate or greater. Given these factors (expected glide speeds on the order of 20 m/s or more, the costs of landing and launching are high, the maximum gut capacity low) we suggest that the primary ecological role was a terrestrial walking small prey specialist and/or scavenger. In the largest adults, flight would likely be minimized to extreme cases like escape or long-distance migration, with the daily locomotion primarily done terrestrially, though juveniles were likely more aerial. Given the lack of mid-sized carnivores in the environment Quetzalcoatlus likely used its size to intimidate smaller rivals such as Saurornitholestes, while feeding on similar sized prey. It was not in competition with sub adult or mature Tyrannosaurs, nor preying on all but the smallest members of the dinosaurian fauna. Thus, we suggest it played the role of a lower trophic level consumer and not an apex predator.

Publication Date

2024

Flying through the air with the greatest of ease? Evaluation of glide capability in basal maniraptoran theropods

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