Gaps in the Rock and Fossil Records and Implications for the Rate and Mode of Evolution

There are three varieties of gaps commonly found in the fossil record. Real gaps are those which cannot be filled. They may result from non-deposition, non-preservation, metamorphism or erosion. The other varieties of gaps are both artificial. Imaginary gaps often result from incorrect beliefs in directed gradual evolution and are defined by rapid morphologic jumps. Temporary gaps result from our limited sampling of fossiliferous strata and may be partially or completely filled by future discoveries. Recently, much attention has been focused on resolution studies which attempt to constrain the amount of time represented by the rock record. This has been in part inspired by a renewed controversy concerning the rate and mode of evolution. There are two extremes in evolutionary thought on this question. The more traditional approach, which has been called phyletic gradualism, holds that constant gradual change leads to the evolution of new species. The more recently developed punctuated-equilibria model hold...