44-1 Living Life in the Slow Lane?: Geochemical Analyses of Brachiopod Hinges Reveal Lifespans and Ocean Energetics through Time

Session: Paleontology, Paleoecology/Taphonomy, Phylogenic Morphological Patterns (Posters)

Presenting Author:

Authors:

Abstract:

Brachiopods are one of the most abundant fossils in the Paleozoic, and they persist into the modern. While their diversity, morphology, and ecology have been extensively studied, we know surprisingly little about their life histories. Life history, specifically lifespan, can inform ecological context because of the connection to organism metabolism and environmental energetics, where a longer lifespan implies a slower metabolism and vice versa. Brachiopod lifespan data offer an opportunity to test Bambach’s ‘seafood through time’ hypothesis, which posits that ocean energetics have increased from the Paleozoic into the modern.

Despite being accretionary, resolving and counting annual growth increments in brachiopod shells has proven difficult, hence the scarcity of available data. To address this, we use geochemical techniques along brachiopod hinges. Brachiopod hinges preserve a complete accretionary record, tend to be thick and well preserved, and consist largely of secondary shell layer that is less likely to experience diagenesis. We utilize micro x-ray fluorescence (microXRF) and laser ablation inductively coupled plasma mass spectometry (LA-ICP-MS) to collect Sr/Ca ratios that can reveal banding associated with seasonal cycles. Sr partitions into calcite as a function of temperature and growth rate such that higher Sr/Ca indicates both warmer temperatures in ambient seawater and faster growth.

We focus on brachiopods from the Middle Devonian Hamilton Group in the northeastern US, including Spinocyrtia granulosa and Mucrospirifer mucronatus. Reconstructions place the region in the subtropics, ~30º S, where temperature varies seasonally and should make years possible to delineate with Sr/Ca.

If brachiopod lifespans are longer than the average bivalve, which appears to be the case based on preliminary results and modern brachiopod data, we might conclude that brachiopods as a whole have slower metabolisms than bivalves, which dominate modern oceans. This implies that brachiopod ecologies could reflect a Paleozoic ocean dominated by slow-growing, longer-lived, low metabolic rate animals, which differs dramatically from post-Paleozoic oceans. This is in accordance with the ‘seafood-through-time’ hypothesis, allowing us to formally test whether the transition toward bivalve dominance represents a shift to faster-paced oceans going into the Cenozoic. Although this work focuses on a restricted spatio-temporal and taxonomic scale, it offers proof of concept and sets the stage to begin filling a large gap in understanding the ecology of marine ecosystems over the Phanerozoic.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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