Rates of speciation in the fossil record

Data from palaeontology and biodiversity suggest that the global biota should produce an average of three
new species per year. However, the fossil record shows large variation around this mean. Rates of origina-
tion have declined through the Phanerozoic. This appears to have been largely a function of sorting among
higher taxa (especially classes), which exhibit characteristic rates of speciation (and extinction) that di¡er
among them by nearly an order of magnitude. Secular decline of origination rates is hardly constant,
however ; many positive deviations re£ect accelerated speciation during rebounds from mass extinctions.
There has also been general decline in rates of speciation within major taxa through their histories,
although rates have tended to remain higher among members in tropical regions. Finally, pulses of specia-
tion appear sometimes to be associated with climate change, although moderate oscillations of climate do
not necessarily promote speciation despite forcing changes in species' geographical ranges.

Tags: MRM, extinction, sampling, fossils