In contrast, evolutionary biologists like Jay Gould have also discussed the theory of "phyletic gradualism" which attributes speciation to a "slow and steady transformation of entire populations" (Eldredge and Gould, 1972). Much debate surrounds the topic of punctuated equilibrium as a mode of speciation, rather than just being a result of gaps that exist in the fossil record.
An example of punctuated equilibrium is the fossil mollusks of East Africa (Hicke, J.)
Hicke, J. www.webpages.uidaho.edu/~jhicke/.../chapter_09.1_evolution.pdf
Eldredge, N. and Gould, S.J. (1972). Punctuated equilibria: an alternative to phyletic gradualism. In Schopf, Thomas J.M. (ed.). Models in Paleobiology. San Francisco: Freeman, Cooper and Company, pp. 82-115.