Moreover, evidence from the fossil record seemed to undermine the genetically orientated, mutationally based model of evolution. Eldredge and Gould argued that most large-scale patterns in evolution cannot be adequately explained by the accumulation of the types of changes seen in living populations throght time (pp74-75) in other words, they were calling into question the accepted belief that microevolutionary change blends seamlessly into macroevolutionary change.
One study that appears to support the punctuationist model was carried out on a complete and apparently continuous fossil record of freshwater snails and bivalves from the Lake Turkana basin in east Africa. The sequence represented the last 4.5 millions years of evolution of a series of lake-dwelling mollusk species. For long periods in this sequence, the snails and bivalves seem to have settled into an equilibrium hardly at all.