Final answer:
Transitions between geological periods marked by punctuated equilibrium and mass extinctions are most responsible for gaps in the fossil record, rather than gradual evolutionary changes.
Step-by-step explanation:
The transition most responsible for gaps in the fossil record is the concept of punctuated equilibrium versus gradualism. Under the theory of gradualism, the fossil record should show an array of intermediate forms showcasing the slow and continuous transition into new species.
Contrastingly, punctuated equilibrium is characterized by long periods of minimal change (stasis) followed by sudden bursts of significant change, leading to the abrupt appearance of new species in the fossil record. This phenomenon explains why transitional fossils are rare since these rapid changes can result in a few intermediate specimens being preserved. Over time, these rapid transitions can contribute to gaps in the fossil record, with new species appearing without a clear sequence of ancestral forms.
The transitions between geological periods often coincide with the five mass extinctions observed in the fossil record, which can also create discrepancies in the continuity of fossil evidence due to the dramatic loss of species.