絶滅

The Cretaceous-Paleogene boundary marks the geological transition between the Cretaceous and Paleogene periods, coinciding with the Chicxulub impact event. This boundary is significant because it represents a major extinction event that caused dramatic changes in diversity across many taxa. By analyzing fossil data before and after this boundary, scientists can understand how different organisms responded to this catastrophic environmental disruption.

Paleontologists use the Paleobiology Database to download diversity data organized by geological stage and taxon. They extract the number of genera occurrences for each time interval, which represents how many organisms existed during that period. By plotting these occurrence counts against time in millions of years ago, researchers create line graphs that visually display diversity trends and identify periods of increase, decrease, or stability across different taxa.

The Paleocene-Eocene Thermal Maximum occurred approximately 55.5 million years ago during the Paleogene epoch, representing a temperature spike of about 8 degrees Celsius above today's average. This thermal event may have affected diversity in certain taxa differently, causing some organisms to thrive while others declined. Analyzing diversity graphs at this point reveals which taxa were sensitive to rapid climate warming and which were resilient to this environmental change.

The experimental hypothesis predicts that many taxa will show changes in diversity following the Cretaceous-Paleogene event and again at the end of the Paleogene, with some increasing while others decrease. The null hypothesis states that no changes in diversity will occur between taxa after these events. Comparing actual fossil data against these predictions helps determine whether environmental factors or random processes drove extinction patterns.

After downloading comma-separated values from the Paleobiology Database, copy each relevant column into a new spreadsheet sheet. Label each sheet with the taxon name, data collection date, and source. Keep data from multiple taxa on the same sheet if clearly labeled and distinct. This organization ensures accurate tracking of which data corresponds to which organisms and prevents confusion when creating multiple graphs for comparison.

Setting taxonomic resolution to genera provides an appropriate level of detail for analyzing diversity changes across geological time. Genera represent a meaningful taxonomic rank that balances specificity with data availability in the fossil record. Using genera allows researchers to track broader evolutionary patterns while maintaining enough resolution to detect significant diversity shifts in response to extinction events and environmental changes.

By making initial predictions about which taxa would increase or decrease in diversity, then comparing these predictions to actual fossil data, researchers can evaluate whether their proposed contributing factors were accurate. If predictions match results, the proposed causes are supported. If they diverge, scientists must reconsider alternative explanations, such as climate change, competition, or resource availability, leading to deeper understanding of extinction mechanisms.