138-5 Loss of functional diversity drives homogenization in Cretaceous - Paleogene Bryozoa at Stevns Klint, Denmark

Session: The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms

Presenting Author:

Maya Samuels-Fair

Authors:

Samuels-Fair, Maya¹, Kahn, Leah², Stewart, Da'shaun³, Archer, Tex⁴, Roque, Guillermo⁵, De Marco, Vincent⁶, Turki, Saanvi⁷, Sizer, Jasmine⁸, Jimena, Elana⁹, Ierardi, Mariana¹⁰, Birchfield, Etienne¹¹, Goines, Isabella¹², Castlevetro, Lucca¹³, Chow, Seth¹⁴, Finnegan, Seth¹⁵

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 Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6860

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.