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Evolution of moa sexual dimorphism

From: Ben Creisler

A new non-dino paper of interest:

Valérie A. Olson and Samuel T. Turvey (2013)
The evolution of sexual dimorphism in New Zealand giant moa (Dinornis)
and other ratites.
Proceedings of the Royal Society: B 280(1760)  20130401 (advance
online publication)
doi: 10.1098/rspb.2013.0401

The extinct giant moa Dinornis is one of the most remarkable known
examples of reversed sexual size dimorphism (RSD), with males weighing
34–85 kg, but females weighing up to 240 kg. However, there has been
little consideration of the evolutionary mechanism that produced this
level of dimorphism, and most living palaeognaths also exhibit varying
levels of RSD. Using male and female body mass data for extant ratites
and tinamous and four extinct moa genera, and tests of phylogenetic
dependence (λ) of body size evolution among these species, we
investigated whether Dinornis was truly unusual with respect to RSD
relative to other palaeognaths, which sex was under greater pressure
to change in size over evolutionary time, and which candidate
hypotheses explaining the presence and variability of RSD in the genus
are most plausible. We demonstrate that the extreme level of RSD
exhibited by Dinornis represents a straightforward consequence of
positive allometric scaling of body size. However, Dinornis females
have undergone more evolutionary change than males, and larger females
from high-productivity environments are associated with greater
differentiation, possibly driven by intraspecific competition and
female-biased selection for increased offspring investment.

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