Abstract
One of the most common responses of marine ectotherms to rapid warming is a reduction in body size, but the underlying reasons are unclear. Body size reductions have been documented alongside rapid warming events in the fossil record, such as across the Pliensbachian-Toarcian boundary (PToB) event (~ 183 Mya). As individuals grow, parallel changes in morphology can indicate details of their ecological response to environmental crises, such as changes in resource acquisition, which may anticipate future climate impacts. Here we show that the morphological growth of a marine predator belemnite species (extinct coleoid cephalopods) changed significantly over the PToB warming event. Increasing robustness at different ontogenetic stages likely results from indirect consequences of warming, like resource scarcity or hypercalcification, pointing toward varying ecological tolerances among species. The results of this study stress the importance of taking life history into account as well as phylogeny when studying impacts of environmental stressors on marine organisms.
Highlights
The most common responses of recent and fossil marine invertebrates to global warming are e xtinctions[1], changes in geographical d istribution2, phenology[3,4], and decreases in body s ize[5,6,7,8,9,10]
Individuals in colder environments grow more slowly but become larger as adults[14]. This widespread pattern is embodied by two well-established hypotheses: Bergmann’s rule, which describes the negative association between temperature and body size in natural environments[15], and the temperature-size rule (TSR)[16], which describes physiological reaction norms relating temperature to body size in laboratory e xperiments[8,11,17,18]
The consensus shape produced through the Generalized Procrustes Analysis (GPA) is a ventral to dorsal profile through an almost cylindrical belemnite rostrum of medium robustness
Summary
The most common responses of recent and fossil marine invertebrates to global warming are e xtinctions[1], changes in geographical d istribution2, phenology[3,4], and decreases in body s ize[5,6,7,8,9,10]. While a decrease in body size has been reported from various past hyperthermal events[25,26,27,28,29,30,31,32,33], morphological changes of different life stages are not commonly s tudied[34] they are crucial for understanding long-term impacts on life history and their ecological implications. We tackle this issue by focusing on one of the most severe extinction crises of the Jurassic: the Pliensbachian-Toarcian crisis. We expect these changes to be correlated with increased temperature, rather than with severe shifts in depositional environments
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