Biological Theory

, Volume 8, Issue 3, pp 245–252 | Cite as

Constraining the Air Giants: Limits on Size in Flying Animals as an Example of Constraint-Based Biomechanical Theories of Form

  • Michael Habib
Thematic Issue Article: Emergence of Shape


The study of biomechanics most often takes a classic adaptationist approach, examining the functional abilities of organisms in relation to what is allowed by physical parameters. This approach generally assumes strong selection and is less concerned with evolutionary stochasticity in determining the presence of biological traits. It is equally important, however, to consider the importance of constraint in determining the form of organisms. If selection is relatively weak compared to stochastic events, then the observed forms in living systems can be taken not as those shapes that were strongly selected for, so much as those forms that do not violate physical rules and therefore persist. Using the problem of maximum animal size as a case study for this alternative biomechanical philosophy, I demonstrate one example of how biomechanical approaches can be used to study constraint and consider the concept of absent forms. This alternative mindset and approach produces a complementary system to the traditional form and function approach in biomechanics. The two philosophies can be used in conjunction to better understand biological systems. I focus particularly on the maximum size of flying animals, as they are a heavily constrained class of system that has also been shaped by substantial stochasticity.


Flight Morphology Pterosauria 



Special thanks to Jeff Schwartz for the invitation to speak and discuss the evolution of form at the KLI in Altenberg. Thanks to James Dean, Storrs Olson, Gary Graves, and Matt Carrano at the National Museum of Natural History (Smithsonian Institution, Washington, DC) and David Hone, Winfried Werner, and Oliver Rauhut for access to specimens at the Bavarian State Collection for Palaeontology and Geology (BSPG, Munich). I am most appreciative of the feedback provided by Catherine Boisvert, David Weishampel, Chris Ruff, Sharon Swartz, and Matt Carrano. Funding graciously provided by the Jurassic Foundation.


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Copyright information

© Konrad Lorenz Institute for Evolution and Cognition Research 2013

Authors and Affiliations

  1. 1.Cell and NeurobiologyUniversity of Southern CaliforniaLos AngelesUSA

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