138 The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms
The Cretaceous-Paleogene boundary interval witnessed extreme geological events: the Chicxulub impact and Deccan Traps volcanism, and a biological catastrophe. New proxy-records, coupled with numerical modelling, unravel the mechanisms driving the environmental change and mass extinction.
Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 304A
Loss of functional diversity drives homogenization in Cretaceous - Paleogene Bryozoa at Stevns Klint, Denmark
Paper number: 138-5
Program: Technical Sessions
Time: 2:40 PM – 2:55 PM
Authors
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Leah KahnStanford University, Palo Alto, CA
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Etienne BirchfieldUniversity of California, Berkeley, Berkeley, CA
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Isabella GoinesUniversity of California, Berkeley, Berkeley, CA
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Lucca CastlevetroUniversity of California, Berkeley, Berkeley, CA
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Seth ChowUniversity of California, Berkeley, Berkeley, CA
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Seth FinneganUniversity of California, Berkeley, Berkeley, CA
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Da'shaun StewartUniversity of California, Berkeley, Berkeley, CA
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Tex ArcherUniversity of California, Berkeley, Berkeley, CA
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Guillermo RoqueUniversity of California, Berkeley, Berkeley, CA
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Vincent De MarcoUniversity of California, Berkeley, Berkeley, CA
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Saanvi TurkiUniversity of California, Berkeley, Berkeley, CA
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Jasmine SizerUniversity of California, Berkeley, Berkeley, CA
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Elana JimenaUniversity of California, Berkeley, Berkeley, CA
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Mariana IerardiUniversity of California, Berkeley, Berkeley, CA
Abstract
Mass extinctions are associated with major faunal turnover at the global scale, but many open questions remain about the local-scale ecological processes that generate global-scale biodiversity patterns. Spatial heterogeneity, generated by a combination of niche partitioning and priority effects, is hypothesized to play an important role in maintaining biodiversity by making ecological communities more persistent and resilient. However, we can rarely observe spatial ecology at high resolution in the fossil record. In this study, we use Bryozoa from Stevns Klint, Denmark, to compare spatial heterogeneity in taxonomic and functional diversity before and after the Cretaceous – Paleogene (K-Pg) mass extinction. We took 23 samples across replicate spatial gradients from the Sigerslev and Højerup Members (latest Maastrichtian) and the Korsnœb Member (earliest Danian). All three members consist of comparable subtidal bryozoan-supported reef mounds. We sieved, imaged, and identified all bryozoan fragments > 2 mm, building a database of 4,453 specimens.
We find the K-Pg mass extinction is associated with both extirpation of genera and turnover of species within genera. The habitat specialists became rare, replaced by opportunistic generalists. This decrease in functional diversity drove the loss of niche partitioning and the loss of priority effects, creating spatial homogeneity. The post-extinction ecological community does not resemble any pre-extinction community across the spatial gradient. Although this study is local in scope, it contrasts the ecological trends found in molluscs from the Cretaceous - Paleogene boundary. Future work will investigate corresponding changes in biomass and the diversity of non-bryozoan taxa at Stevns Klint.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-412465
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