The Earth has entered a period of accelerated extinctions. Many long-lived groups are now becoming threatened, including ones such as sharks that have survived for millions of years. A critical question is how our current loss of species compares to the "Big Five" mass extinctions from the geologic past, when up to 90% of all species on earth went extinct, and recovery took millions of years.

 In this project, our goal was to look for a leading indicator that would predict how current species loss compares to historical mass extinctions. We looked at the selectivity of extinctions -- not just how many species, but which species are going extinct or becoming threatened with extinction. Specifically, we focused on the age selectivity of extinctions: whether older groups (ones that had existed earlier in geologic time) or younger groups are more likely to go extinct.

 Previous research on the fossil record has shown that older groups were generally less likely to go extinct at any given time over the last 500 million years. This is not surprising, as older groups might have had more time to evolve beneficial adaptations, or to spread across a larger area of the earth. However, this pattern did not hold during mass extinctions, when older groups had no advantage over younger groups. Apparently, whatever beneficial traits older groups had were not enough to save them during catastrophic events such as massive volcanic activity or an asteroid impact.

 In this project, we quantified extinction risk of modern groups using the IUCN Red List, a database that classifies species as near threatened, vulnerable, endangered, etc. Using the statistical technique of logistic regression, we found that extinction risk of modern groups did not depend on the age of the group. In other words, the modern extinction crisis resembles the Big Five mass extinctions in terms of age selectivity. This conclusion underscores the seriousness of our current threats to earth's species.

 We published three refereed conference abstracts funded by the grant, and we are currently preparing a manuscript for submission to a peer-reviewed journal. We also presented talks on our work at the Geological Society of America, the Mathematics of Mass Extinctions Research Network, the University of Pennsylvania, Temple University, and Syracuse University. 

 The project provided research experience for seven undergraduate students and recent graduates, who learned about using statistical methods to quantify modern extinctions and using historical data from paleontological databases. They also gained experience in communicating science by presenting posters on their work at the Geological Society of America Annual Meeting, a Royal Society (UK) conference on conservation paleobiology, and Swarthmore Sigma Xi poster sessions. 

 We also created a lesson plan on ocean acidification and modern extinctions, which was used in a summer enrichment program for middle school students from a nearby underserved school district. This lesson plan was submitted to the Teach the Earth teaching repository

Last Modified: 03/20/2025
Modified by: Steve C Wang