291 Cephalopods Through Time: Insights into Evolution, Ecology, and Environmental Reconstruction

This session explores cephalopod biology, ecology, and evolution, highlighting their role in paleoenvironmental reconstruction. We welcome analytical and computational research that advances understanding of these organisms, providing new perspectives on their evolution and ecological significance.

Wednesday, 22 October 2025
1:30 PM - 5:30 PM
HBGCC, 304B

The Last Dynasty: quantifying Late Campanian – latest Maastrichtian ammonite paleobiogeography

Paper number: 291-1
Program: Technical Sessions
Time: 1:35 PM – 1:50 PM

Authors

Abstract

Ammonoid paleobiogeography during the last 10 Myrs of the Cretaceous has not been studied quantitatively on a global scale. Some observations of similarities between geographically separated faunas have been noted in biostratigraphic studies, primarily comparing the Mediterranean Tethys, North America, and the Boreal Chalk Sea. Recent studies show molluscan fauna (including ammonites) from the Western Interior Seaway (WIS) and the Gulf Coastal Plain (GCP) of North America are statistically grouped within the same biogeographic unit. This study combines the most updated Cretaceous ammonoid database, with new and unpublished data from Late Campanian-Maastrichtian localities in the Caribbean Tethys (Chiapas, Cuba, Jamaica, Costa Rica). Similarity Indexes and NMDS-style ordination analyses were used to explore the demarcation of biogeographic provinces, given this enhanced dataset. Analysis of similarities (ANOSIM) was used to test whether these “provinces” were significantly different.

Late Campanian data shows four main biogeographic provinces: Tethys, Eastern Pacific, Antarctica, and the WIS. Other regions (Western Pacific, Western Africa, Southern Africa, and the Caribbean Tethys) fall between these provinces, but show some similarities based on geographic proximity (showing a combination of biogeographic faunas). Biostratigraphic markers used in the Tethyan province are found in most of the areas (nostoceratids, pachydiscids), but are less abundant in the WIS.

Early Maastrichtian provinciality increases between the different areas, while maintaining the same general pattern of four distinct regions in ordination space. The WIS and Gulf/Atlantic (GCP/ACP) become more separated from the Tethys and other tropical areas during this time. This result is expected given that Tethyan early Maastrichtian ammonite biostratigraphic markers (pachydiscids) are not found commonly in the GCP/ACP. New Caribbean data fits statistically closely with the Tethys and Eastern Pacific, with the expected biostratigraphic markers (diplomoceratids, pachydiscids) and similar biogeographic composition. The same trends are detected in the late Maastrichtian regions, however, there is few late Maastrichtian ammonite data from the Caribbean.

The increased provinciality during the Maastrichtian might result from poor preservation outside these regions, or lack of systematic sampling for ammonites. However, increasing provinciality could result from paleoclimatic trends (i.e., climate cooling beginning in the Campanian) that affected ammonite distribution. These patterns support additional research into the habitat availability and dispersal potential of the last ammonites, giving new insight into their extinction mechanisms.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412390

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