The necks of giraffes are the closest extant equivalent to the necks of sauropod dinosaurs
Two hypotheses have been proposed to explain the functional significance of the necks of giraffes, and those hypotheses can be applied to the necks of sauropods: • Competing browsers hypothesis-The long neck makes more food resources available to a giraffe or sauropod by allowing it to reach upward to browse on vegetation that is not available to short-necked browsers. • Necks-for-sex hypothesis-Males giraffes and sauropods use their necks and heads to batter opposing males during intraspecific combat. Thus, long necks increase the fitness of males by increasing their opportunities to mate. What predictions can you make about the relative lengths of the necks of male and female sauropods to test these hypotheses?
We cannot make direct observations of sauropod feeding and combat, so we need predictions that can potentially be tested with fossils. Here are two examples:
• The necks-for-sex hypothesis predicts that males will have longer necks and larger heads than females, whereas the competing browser hypothesis does not.
• The competing browser hypothesis predicts that sympatric species will have necks of different lengths, whereas the necks-for-sex hypothesis does not.
The hypotheses are not mutually exclusive, and both might be correct.
Sources
Padian, K., and J. R. Horner. 2011 . The definition of sexual selection and its implications for
dinosaurian biology. Journal of Zoology 283:23-27
Simmons, R. E., and R. Altwegg. 2010 . Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe. Journal of Zoology 282:6-12.
Simmons, R. E., and L. Scheepers. 1996 . Winning by a neck: Sexual selection in the evolution of giraffe. The American Naturalist 148:771-786
Taylor, M. P., et al. 2011 . The long necks of sauropods did not evolve primarily through sexual selection. Journal of Zoology 285:150-161
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