Tutoría Biología

Rocks and clocks: calibrating the Tree
of Life using fossils and molecules
Philip C.J. Donoghue and Michael J. Benton
Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK
Agreat tradition in macroevolution and systematics has
been the ritual squabbling between palaeontologists
and molecular biologists. But, because both sides were
talking past each other, they couldnever agree. Practitioners
in both fields should play to their strengths and
work together: palaeontologists can provide minimum
constraints on branching points in the Tree of Life withconsiderable precision, and estimate the extent of unrecorded
prehistory. Molecular tree analysts have remarkable
modelling tools in their armoury to convert multiple
minimum age constraints into meaningfuldated trees.
As we discuss here, work should now focus on establishing
reasonable, dated trees that satisfy rigorous assessment
of the available fossils and careful consideration of
molecular treemethods: rocks and clocks together are
an unbeatable combination. Reliably dated trees provide,
for the first time, the opportunity to explore wider
questions in macroevolution.
The evolvingrelationship between rocks and clocks
Classically, the fossil record has provided the timescale for
evolutionary history. This role was codified as the unique
contribution of palaeontology to theneodarwinian synthesis
by Simpson in his seminal Tempo and Mode in
Evolution [1]. This is, however, no longer the case. There
have been four decades of evolving molecular clock theory
[2] and, since the1990s, this has become the tool of choice
in attempts to calibrate evolutionary time. One might
be seduced into thinking that fossils are no longer of any
use in aworld of molecular biology. Afterall, the fossil record
has been berated countless times for its failure to match
molecular clock estimates for the timing of evolutionary
events. Recently, however, there has been an almost...