Admissions > PhD by research > Research Projects > Constraints and efficiency in the evolution of birds

Constraints and efficiency in the evolution of birds

Supervisor: Dr Emily Rayfield

There is a long standing perception in vertebrate evolutionary studies that the evolution of flight demands a lightening and stiffening of the skeleton to reduce the metabolic cost of locomotion, but without compromising the functional demands emplaced by powerful muscular contractions. This may have been achieved in part by reduction and fusion of skeletal elements and increased pneumatisation of bones. In the cranium we have a notion of birds thinning their skulls, expanding their brains whilst reducing adductor muscle mass, and replacing teeth with a lightweight keratin beak. Indeed, new research (Dumont et al. 2010) has shown that passerine birds have thin but very dense cranial bones, which in turn increases skull stiffness and strength, thereby minimizing bone mass and volume. Is the performance of avian skulls constrained by the need for mass-reduction? Are similar trends observed in volant non-avian dinosaurs? Does possessing thin but dense bones allow bird skulls to circumvent aerial constraints?

This project tests the hypothesis that bird and aerial non-avian dinosaur skulls are more “mechanically efficient” than the skulls of terrestrial and flightless taxa, and converge in terms of their mechanical performance.

Mechanical efficiency can be measured using biomechanical performance metrics, such as strain energy (how much a structure deforms under load), cranial stress and strain distribution and safety factors (ratio of everyday stress to breaking or yield stress). Bones remodel and adapt in response to the loading conditions they experience, with tissue being added or removed in areas of high and low strain levels respectively (Frost 1997). The net end result, in theory, should be that when all loading criteria, such as muscles, bite forces and in some circumstances fascia are considered (Curtis et al. 2011), the skull should be evenly strained if it is performing ‘efficiently’. Computational biomechanical techniques such as finite element analysis (FEA) offer a means to calculate deformation, stress and strain from computer models of skulls created from computed tomography (CT) data, with user engineering and orthopaedic biomechanics, FEA is now quite common in zoological and palaeontological functional studies, including functional studies of dinosaurs and birds (see Rayfield 2007, 2011).

Significance/novelty: This will provide a unique insight into how mechanical factors influence cranial morphology in a range of taxa subject to varying environmental constraints during the evolution of birds.

Recommended reading:

Last updated: 22/12/11