■■The per taxon rate of diversification equals the
rate of origination (or speciation) minus the rate
of extinction. Analyses of diversity in the fossil
record require procedures to correct for biases
caused by the incompleteness of the record.
some inferences about rates of diversification
and speciation can also be made from time-
calibrated phylogenies of living species.
■■The diversity of skeletonized marine animals has
increased during the Phanerozoic, but at vary-
ing rates. Diversity appears to have increased
in the Cambrian to an approximate equilibrium
that lasted for most of the Paleozoic; then, after
the mass extinction at the end of the Permian, it
has increased, with interruptions and at varying
rates, ever since.
■■The background rate of extinction (in between
mass extinctions) has declined during the Pha-
nerozoic, perhaps because higher taxa that were
particularly susceptible to extinction became
extinct early.
■■f ve mass extinctions (at or near the ends of the i
ordovician, Devonian, Permian, Triassic, andCretaceous) are recognized. These periods of
high extinction rates have been followed by
intervals of rapid origination of new taxa. Their
diversification was probably released by the
extinction of taxa that had occupied similar
ecological space. newly diversifying groups
have sometimes replaced other taxa by direct
competitive displacement, but more often they
have replaced incumbent taxa after those taxa
became extinct.
■■The increase in diversity over time appears
to have been caused mostly by adaptation to
vacant or underused adaptive zones (“ecological
space”), and by the evolution of key adaptations.
Diversity has also been affected by biological in-
teractions, whereby new species are often used
as resources by other species.
■■Both paleontological and phylogenetic evi-
dence shows that the increase in diversity in
most clades has been diversity-dependent. such
observations imply that diversity tends toward
an equilibrium, but diversity seems nevertheless
to increase, partly because new and specialized
ways of living continue to evolve.TERMs AnD ConCEPTs
background
extinction
diversity-
dependent factorecological
opportunity
key adaptationlineage-through-
time (LTT) plot
mass extinction
pull of the RecentRed Queen
hypothesis
species richness
species selectionsuggEsTions foR fuRTHER READing
Many of the topics in this chapter are treated
clearly in Principles of Paleontology (third edi-
tion) by M. foote and A. i. Miller (W. H. free-
man, new york, 2007). see also D. Jablonski et
al. (eds.), Evolutionary Paleobiology (univer-
sity of Chicago Press, 1996).
The end-Permian mass extinction is the subject
of a popular book by D. H. Erwin, Extinction:
How Life on Earth Nearly Ended 250 Million
Years Ago (Princeton university Press, Princ-
eton, nJ, 2006). The consequences of mass
extinctions are reviewed by R. K. Bambach, in
“Phanerozoic biodiversity mass extinctions”
(Annu. Rev. Earth Planet. Sci. 34: 127–155,
2006), and D. Jablonski, in “Mass extinc-
tions and macroevolution” (Paleobiology 31
[supp.]: 192–210, 2005).Adaptive radiation is treated by R. E. glor’s
“Phylogenetic insights on adaptive radiation”
(Annu. Rev. Ecol. Evol. system. 41: 251–270,
2010), and at greater length by D. schluter in
The Ecology of Adaptive Radiation (oxford
university Press, oxford, uK, 2010).
Current phylogenetic methods for studying
diversification are reviewed by R. A. Pyron
and f. T. Burbrink in “Phylogenetic estimates
of speciation and extinction rates for test-
ing ecological and evolutionary hypotheses”
(Trends Ecol. Evol. 28: 729–736, 2013). Con-
trasting views on whether or not diversity is
constrained by ecological limits are presented
by l. J. Harmon and s. Harrison in “spe-
cies diversity is dynamic and unbounded at
local and continental scales” (Am. Nat. 185:suMMARy
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