Polonica 42, 1, 1-12 (1997)
Trammer, J. & Kaim, A.
Abstract. Cope's rule concerns only the radiation
phase of a clade, overlooking the phase of the clade decline; thus it is
incomplete. Changes of body size during the entire evolutionary history of a
clade are exemplified here by three trilobite groups - Ptychopariina, Asaphina
and Phacopida. Increasing diversity of the clade is associated with increase
in maximum body size during the radiation phase, and decreasing diversity is
generally associated with a decrease in maximum body size. Two basic patterns
of the maximum body size changes are observed during the decline of the clade.
The first one is characterized by a high correlation between diversity and the
maximum body size, and indicative of species attrition that is nonselective
with respect to the body size. The second one is characterized by a weak
correlation between diversity and maximum body size, and typical of selective
species attrition in relation to size.