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Macroevolutionary trends in the Dinosauria: Cope's rule

During recent years Cope's rule repeatedly has been tested among extant taxa 
(most notably birds, reptiles, mammals), with quite different results re its 
'validity'. Now list-members will be pleased with the following study showing 
that dinosaurs were congruent with Cope's rule: they got larger all the time. 
(Oh, erm, well, little birds are exceptional, of course, as well as the 
largestest dinosaurs: they tend to get smaller). 

Kind regards

Markus Moser

Journal of Evolutionary Biology

Macroevolutionary trends in the Dinosauria: Cope's rule

Cope's rule is the tendency for body size to increase over time along a 
lineage. A set of 65 phylogenetically independent comparisons, between earlier 
and later genera, show that Cope's rule applied in dinosaurs: later genera were 
on average about 25% longer than the related earlier genera to which they were 
compared. The tendency for size to increase was not restricted to a particular 
clade within the group, nor to a particular time within its history. Small 
lineages were more likely to increase in size, and large lineages more likely 
to decrease: this pattern may indicate an intermediate optimum body size, but 
can also be explained as an artefact of data error. The rate of size increase 
estimated from the phylogenetic comparisons is significantly higher than the 
rate seen across the fauna as a whole. This difference could indicate that 
within-lineage selection for larger size was opposed by clade selection 
favouring smaller size, but data limitations mean that alternative !
 explanations (which we discuss) cannot be excluded. We discuss ways of 
unlocking the full potential usefulness of phylogenies for studying the 
dynamics of evolutionary trends.

Dr. Markus Moser
Staatliches Museum fuer Naturkunde Stuttgart
Museum am Loewentor (= Rosenstein 1)
D-70191 Stuttgart
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