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Cope's rule and ceratopsian frill ornamentation

Ben Creisler

A new advance online paper:

Pasquale Raia, Federico Passaro, Francesco Carotenuto, Leonardo
Maiorino, Paolo Piras, Luciano Teresi, Shai Meiri, Yuval Itescu, Maria
Novosolov, Mattia Antonio Baiano, Ricard Martínez and Mikael Fortelius
Cope’s Rule and the Universal Scaling Law of Ornament Complexity.
American Naturalist 186 (2): (advance online publication)
DOI: 10.1086/682011
http://www.jstor.org/stable/amernatu.ahead-of-print  [not yet posted on JSTOR]

pdf downloadable here:


Luxuriant, bushy antlers, bizarre crests, and huge, twisting horns and
tusks are conventionally understood as products of sexual selection.
This view stems from both direct observation and from the empirical
finding that the size of these structures grows faster than body size
(i.e., ornament size shows positive allometry). We contend that the
familiar evolutionary increase in the complexity of ornaments over
time in many animal clades is decoupled from ornament size evolution.
Increased body size comes with extended growth. Since growth scales to
the quarter power of body size, we predicted that ornament complexity
should scale according to the quarter power law as well, irrespective
of the role of sexual selection in the evolution and function of the
ornament. To test this hypothesis, we selected three clades
(ammonites, deer, and ceratopsian dinosaurs) whose species bore
ornaments that differ in terms of the importance of sexual selection
to their evolution.We found that the exponent of the regression of
ornament complexity to body size is the same for the three groups and
is statistically indistinguishable from 0.25.We suggest that the
evolution of ornament complexity is a by-product of Cope’s rule. We
argue that although sexual selection may control size in most
ornaments, it does not influence their shape.


Notice of publication: