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101-8 Anoxia-Driven Change in Community Composition at the Norian–Rhaetian Boundary in Panthalassa

Session: Mass extinctions and the current biodiversity crisis: Lessons from the past to inform the future (Part I)

Presenting Author:

Lena Jude Lacherez

Authors:

Lacherez, Lena Jude¹, Ramirez-Guasp, Fiorella S.², Bingham, Joseph D.³, Tackett, Lydia S.⁴, Dineen, Ashley A.⁵, Banker, Roxanne M.W.⁶, Roopnarine, Peter D.⁷, Tyler, Carrie L.⁸r> (1) Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV, USA, (2) Department of Geoscience, University of Nevada Las Vegas, Las Vegas, Nevada, USA, (3) Department of Geoscience, University of Nevada Las Vegas, Las Vegas, Nevada, USA, (4) School of Earth, Environment, and Sustainability, Missouri State University, Springfield, MO, USA, (5) UC Museum of Paleontology, Berkeley, CA, USA, (6) Department of Biology, Providence College, Providence, RI, USA, (7) Department of Invertebrate Zoology and Geology, California Academy of Sciences, San Francisco, CA, USA, (8) Department of Geoscience, University of Nevada, Las Vegas, NV, USA,

Abstract:

Shallow‑marine ecosystems today are increasingly threatened by anoxia. Ancient intervals of oxygen stress, such as the Late Triassic Norian–Rhaetian Boundary (NRB), provide critical analogues for understanding long-term ecological responses. The Gabbs Formation (Norian-Hettangian) in New York Canyon (western‑central Nevada, USA) preserves a stratigraphically continuous fossil record across the NRB from eastern Panthalassa, allowing us to evaluate the effects of anoxia on marine ecosystems.

Here, we assess changes in community composition across the NRB by compiling taxonomic occurrences from the shallow marine Gabbs Formation representing 9 phyla. Bulk field sampling resulted in a total of 497 specimens, with 24 Norian samples containing 57 genera, compared to 9 Rhaetian samples containing 28 genera. Community composition was compared using Non‑metric Multidimensional Scaling (NMDS) based on Bray-Curtis dissimilarities, alongside cluster analysis and environmental correlation vectors of redox proxy data (Mn, Sr, δ¹³C, δ¹⁸O) and ecological traits (feeding and motility). PERMANOVA indicates minimal overlap in species composition between the Late Norian and Rhaetian intervals (p = 0.001). Community composition was weakly, but significantly, correlated with manganese concentrations (R² = 0.32, p = 0.03), an established proxy for anoxia, suggesting that worsening oxygen stress played a central role in community restructuring.

Across the NRB, 63% of taxa were lost in New York Canyon. Four motility types (sessile unattached, facultative slow, facultative fast, fully mobile slow) were significantly correlated with community change, suggesting motility was a strong predictor of survivorship. In addition, both the suspension feeders (R2 = 0.25, p = 0.001) and predatory lifestyles (R2 = 0.36, p = 0.001) had significant effects on taxonomic losses, while deposit feeders did not. This is likely caused by the limited mobility of many suspension feeders, while some highly mobile predators may have been able to forage outside of anoxic zones. Deposit feeders likely thrived in the early stages of the perturbation, as accumulating organic remains would have initially provided ample food sources. These results demonstrate substantial changes in an ancient shallow‑marine ecosystem under sustained deoxygenation, offering a deep-time analogue for modern coastal ecosystem decline.

Anoxia-Driven Change in Community Composition at the Norian–Rhaetian Boundary in Panthalassa

Description

Session Format: Oral

Presentation Date: 10/12/2026

Presentation Start Time: 09:55 AM

Presentation Room: CCC, Bluebird Ballroom 3A

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