Editor: Steven Le Comber
The evolution of ‘bizarre structures’ in dinosaurs: biomechanics, sexual selection, social selection or species recognition?
Article first published online: 8 JUN 2010
© 2010 The Authors. Journal of Zoology © 2010 The Zoological Society of London
Journal of Zoology
Volume 283, Issue 1, pages 3–17, January 2011
How to Cite
Padian, K. and Horner, J. R. (2011), The evolution of ‘bizarre structures’ in dinosaurs: biomechanics, sexual selection, social selection or species recognition?. Journal of Zoology, 283: 3–17. doi: 10.1111/j.1469-7998.2010.00719.x
- Issue published online: 22 DEC 2010
- Article first published online: 8 JUN 2010
- Received 14 October 2009; revised 4 February 2010; accepted 22 April 2010
- functional morphology;
- sexual selection;
- social selection;
- species recognition
‘Bizarre structures’ in dinosaurs have four main traditional explanations: mechanical function, sexual selection, social selection and species recognition. Any of these can be plausible for individual species, but they fail to be persuasive when other lines of evidence cannot adequately test them. The first three also fail as general propositions when phylogenetic analyses based on other characters do not support scenarios of selective improvement of such functions in their clade (or the explanation simply does not apply to any other species in the clade). Moreover, the hypothesis of sexual selection requires significant sexual dimorphism, which has never been conclusively established in dinosaurs.
We propose instead that species recognition may have been a more general force that drove the evolution of bizarre structures in dinosaurs. That is, the bizarre structures communicate to other individuals a variety of possible associational cues, including species identification, potential protection and social habits and the appropriateness of potential mates. In other words, bizarre structures amount to an advertisement for positive association. Neither species recognition nor any other hypothesis should be a ‘default’ explanation. Although direct observation is impossible, we propose two tests. First, contrary to adaptive, social or sexual selection, under the species recognition model morphology should be expected to evolve without obvious directional trends, because the only objective is to differ from one's relatives. Hence, patterns of evolution of bizarre structures should be relatively proliferative and non-directional. Second, several contemporaneous species should overlap in geographic range (sympatric, parapatric, peripatric). Fossil species often show evidence of this pattern in the past by ‘ghost ranges’ of related taxa. These tests together could reinforce or weaken an argument for species recognition.