Young-Earth creationists believe that speciation was uncommon in which period?

Young-Earth creationists typically argue that significant changes in species, or speciation, were infrequent during the Post-Flood Epoch because they believe that the Earth's history is relatively short, dating back only a few thousand years. This perspective holds that after a global flood, as described in religious texts, the resulting environments were so drastically altered that few new species emerged beyond those that survived the flood. This period is viewed by young-Earth creationists as one where the ability for species to evolve or diversify was severely limited due to environmental factors, genetic constraints, and the offspring of the types of organisms that managed to survive the flood.

In contrast, the Pre-Flood Epoch is often seen as a time of greater diversity due to its depiction as a period ripe for extensive and rapid change before the flood event. The Paleozoic and Mesozoic eras, which feature vast geological time scales and rich fossil records, are viewed within the context of evolution by other scientific paradigms, which may conflict with the young-Earth perspective. However, young-Earth creationist views place the most emphasis on the Post-Flood Epoch as a time of restricted speciation, aligning with their interpretation of biblical narratives and a literal reading of Earth’s history.