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Dinosaur and pterosaur head crest evolution by sexual selection

From: Ben Creisler
A new online paper:
Does mutual sexual selection explain the evolution of head crests in pterosaurs 
and dinosaurs?
Lethaia (advance online publication)
DOI: 10.1111/j.1502-3931.2011.00300.x
Cranial ornamentation is widespread throughout the extinct non-avialian 
Ornithodira, being present throughout Pterosauria, Ornithischia and Saurischia. 
Ornaments take many forms, and can be composed of at least a dozen different 
skull bones, indicating multiple origins. Many of these crests serve no clear 
survival function and it has been suggested that their primary use was for 
species recognition or sexual display. The distribution within Ornithodira and 
the form and position of these crests suggest sexual selection as a key factor, 
although the role of the latter has often been rejected on the grounds of an 
apparent lack of sexual dimorphism in many species. Surprisingly, the 
phenomenon of mutual sexual selection -- where both males and females are 
ornamented and both select mates -- has been ignored in research on fossil 
ornithodirans, despite a rich history of research and frequent expression in 
modern birds. Here, we review the available evidence
 for the functions of ornithodiran cranial crests and conclude that mutual 
sexual selection presents a valid hypothesis for their presence and 
distribution. The integration of mutual sexual selection into future studies is 
critical to our understanding of ornithodiran ecology, evolution and 
particularly questions regarding sexual dimorphism.