Résumé
The use of nucleotide and amino acid sequences allows improved
understanding of the timing of evolutionary events of life on earth.
Molecular estimates of divergence times are, however, controversial and
are generally much more ancient than suggested by the fossil record. The
limited number of genes and species explored and pervasive variations in
evolutionary rates are the most likely sources of such discrepancies. Here
we compared concatenated amino acid sequences of 129 proteins from 36
eukaryotes to determine the divergence times of several major clades,
including animals, fungi, plants, and various protists. Due to significant
variations in their evolutionary rates, and to handle the uncertainty of
the fossil record, we used a Bayesian relaxed molecular clock
simultaneously calibrated by six paleontological constraints. We show
that, according to 95% credibility intervals, the eukaryotic kingdoms
diversified 950–1,259 million years ago (Mya), animals diverged from
choanoflagellates 761–957 Mya, and the debated age of the split between
protostomes and deuterostomes occurred 642–761 Mya. The divergence times
appeared to be robust with respect to prior assumptions and
paleontological calibrations. Interestingly, these relaxed clock time
estimates are much more recent than those obtained under the assumption of
a global molecular clock, yet bilaterian diversification appears to be
≈100 million years more ancient than the Cambrian boundary.