Since the divergence, from the fossil record, is older than the molecular data indicate, the discrepancy is probably due to problems with the calibration of the molecular clock. This could be due to a lower-than-expected mutation rate in the organism being studied or to some mutations which reversed earlier changes, camouflaging the amount of change which had occurred and, thus, the amount of time involved.
Work Step by Step
This question asks you to see that the molecular clock is not an infallible tool-- a researcher must consider things like variation in mutation rate while using it. Review Concept 26.5.