Insights into mass estimation, pneumaticity, and anatomy of pterosaurs: implications for locomotion

Abstract

Pterosaurs were both the first and largest vertebrates to achieve powered flight, surviving for over 150 million years, and ranging in size from 0.5-11m wingspans. This large size was achieved through a number of adaptations, including a membraneous wing supported by a single elongated finger, a strongly developed forelimb, and a pneumatised skeleton with hollow bones. This thesis aims to quantify aspects of pterosaur pneumaticity, mass estimation, and wing bone morphology and deduce how these relate to pterosaur locomotion and flight. Using computed tomography (CT), the internal structure of pterosaur bones is visible, and the degree of pneumaticity is compared to other animals, indicating large pterosaurs were among the most pneumatised animals. A large database of pterosaur wing bone geometry and cross-sections shows that small pterosaurs were biomechanical generalists, resistant to loads both common in flight and terrestrial locomotion, while most larger pterosaurs sacrificed terrestrial capabilities in favour of low mass and resisting increased loads in flight. To better understand pterosaur body mass, a study of avian mass found that the relationship between skeletal mass and total mass may be accurate in neornithine birds, but should not be expanded to pterosaurs. Related, validation tests show that CT scans can be used to accurately estimate bone mass and volume, which can be incorporated into pterosaur mass studies. Building on this, a 3D skeletal reconstruction of an individual Coloborhynchus was used in a detailed estimate of the volume and mass of a single individual, in order to compare results from different methods. Although arguably subjective, 3D reconstruction more accurately represents the soft tissue than a minimum convex hull method, and is better at estimating mass than skeletal correlates such as humeral circumference. Finally, investigation of large pneumatic foramina in the sacrum of a small-bodied pterosaur lead to the identification of spinal nerve foramina in the first study of pterosaur postcranial neurology. Differences in neural canal size reveal potential patterns in locomotion, with some animals having highly innervated hind limbs, while others have relatively poor innervation. This thesis provides new information on mass estimation in pterosaurs, pneumaticity, wing bone geometry, and locomotory patterns. Together, these results show that while some pterosaurs were the most pneumatic animals, there is significant variability, overturning conventional wisdom. This builds on previous ideas of pterosaur locomotion, giving more evidence to the idea that most larger, more-derived pterosaurs were optimised for flight, while smaller, more-basal pterosaurs were generalists.

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