The profound transformations that shaped the marine ecosystems during the mid-Cretaceous period continue to captivate paleontologists and geoscientists alike. A recent study, presented at the 2025 General Assembly of the European Geosciences Union, sheds new light on the dramatic shifts in marine reptile communities during the Cenomanian-Turonian transition — a time marked by extreme climatic events and global oceanic changes. This interval, roughly 93.9 million years ago, stands out as one of the hottest periods in the last half a billion years, characterized by unprecedented carbon dioxide concentrations and fluctuating ocean chemistry, likely altering the entire structure of marine food webs.
Before this transition, Late Jurassic and Early Cretaceous oceans were dominated by apex predators such as formidable pliosaurids with massive jaws extending up to two meters, swift ichthyosaurs reminiscent of modern dolphins, and predatory crocodyliforms known as thalattosuchians. These taxa held ecological dominance for tens of millions of years, shaping the food chain architecture in marine environments. However, the fossil record reveals an abrupt and widespread extinction event during the Cenomanian-Turonian boundary, whereby these keystone predators vanished almost entirely. This sudden die-off paved the way for the diversification of mosasaurs, plesiosaurs, and various shark species, dramatically reshaping marine predation strategies.
Valentin Fischer and his research team at the Université de Liège approached this complex biological turnover by integrating phylogenetic data from hundreds of marine reptile lineages. Leveraging both two-dimensional and three-dimensional morphological datasets—the largest assemblage of such data ever compiled—the team investigated how extinction patterns corresponded with shifts in predatory traits and functional capabilities. Their analyses demonstrate that extinctions disproportionately affected large-bodied and fast-swimming predators, resulting in a sequential rather than instantaneous collapse of these groups.
One striking finding centers on the alterations in skull morphology before and after the transition. Changes in cranial shape closely correlate with biomechanical attributes such as bite force and feeding strategies. Predators that once relied on speed and powerful jaw mechanics gave way to species with markedly different morphologies and functional anatomies. This morphological turnover highlights not only the taxonomic but also the ecological restructuring within marine guilds, indicating a fundamental shift in ecosystem dynamics.
Crucially, the underlying environmental drivers are linked to ocean anoxia and climatic instability during the Cenomanian-Turonian event. Known as one of the most severe oceanic anoxic events (OAE) in the Phanerozoic Eon, this interval witnessed widespread depletion of oxygen in the oceans, severely impacting marine life. Elevated greenhouse gas concentrations, particularly of carbon dioxide, generated climatic volatility that disrupted nutrient cycles, including sulfur and iron availability. These changes cascade through marine ecosystems, constraining the survival and adaptability of top predators highly dependent on specific environmental conditions.
This research also emphasizes the importance of combining phylogenetic and functional morphology frameworks to decipher extinction dynamics. By mapping extinction rates and shifts in predatory capabilities onto evolutionary trees, the study provides nuanced insight into how selective pressures functioned at different evolutionary scales. It appears that extinction was not random but instead targeted species exhibiting particular traits—specifically, those occupying upper trophic levels with high energy demands and specialized hunting methods.
The extinction and subsequent ecological turnover had profound implications for marine biodiversity and ecosystem functioning. The rise of mosasaurs and plesiosaurs after the mid-Cretaceous event signified a reorganization of marine predator-prey interactions. Mosasaurs, for example, evolved elongated bodies and robust jaws capable of subduing a broad range of prey, effectively filling niches left vacant by extinct pliosaurids and ichthyosaurs. This new assemblage of predators formed oceanic food webs distinct from their Jurassic and Early Cretaceous predecessors, highlighting evolutionary innovation triggered by environmental upheaval.
The study also provides a window into the tempo and mode of marine reptile extinctions, indicating a stepwise decline rather than a sudden extinction pulse. Such patterns suggest that environmental stressors may have progressively limited the viability of certain clades, leading to cascading ecological consequences. Understanding these patterns is critical for comprehending the resilience and vulnerability of marine ecosystems to rapid climate change, both in the deep past and potentially in the modern era.
Furthermore, mechanistic investigations into bite force evolution reveal that shifts in predatory performance were tightly coupled to extinction dynamics. Changes in cranial architecture reflected adaptations to new prey types, hunting techniques, or ecological constraints induced by fluctuating oceanic conditions. These biomechanical transformations underscore the intricate relationship between environmental change and organismal functional traits, illustrating how extinction events can drive evolutionary innovation and diversification.
Fischer’s team will expand on these findings in a dedicated session on mass extinctions during the Earth’s history, presented at EGU 2025. This contribution not only enriches our understanding of the mid-Cretaceous extinction event but also provides a methodological blueprint for studying marine extinction patterns by bridging paleontology, phylogeny, and functional morphology. Their data-intensive approach paves the way for future investigations into how ancient climate crises shaped the evolutionary trajectories of oceanic life.
The implications of this research extend beyond paleobiology. By elucidating the responses of marine apex predators to past climate extremes, it offers valuable analogs for predicting how modern marine ecosystems might respond to ongoing anthropogenic environmental changes. With ocean deoxygenation and climate warming accelerating in today’s seas, the mid-Cretaceous record provides a cautionary tale about ecosystem fragility and the potential for rapid faunal turnovers.
In conclusion, the Cenomanian-Turonian transition stands as a pivotal moment in Earth’s history where extraordinary climate volatility induced a major restructuring of marine food webs. The disappearance of iconic Jurassic predators and emergence of novel Cretaceous marine reptiles exemplifies the deep evolutionary consequences of oceanic anoxic events and greenhouse-driven environmental perturbations. Through cutting-edge phylogenetic and morphometric analyses, researchers have unraveled key aspects of this ancient crisis, demonstrating the power of multidisciplinary approaches to unravel the complex tapestry of life’s history.
Subject of Research: Not applicable
Article Title: How mid-Cretaceous events affected marine top predators
News Publication Date: Not explicitly stated; presented at the EGU General Assembly on 01 May 2025
Web References: https://doi.org/10.5194/egusphere-egu25-3100
References: Fischer, V., Della Giustina, F., Bennion, R., and MacLaren, J.: How mid-Cretaceous events affected marine top predators, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3100
Image Credits: Valentin Fischer, Francesco Della Giustina
Keywords: Cenomanian-Turonian transition, mid-Cretaceous extinction, marine reptiles, pliosaurids, ichthyosaurs, mosasaurs, ocean anoxia, phylogenetics, functional morphology, carbon dioxide, climate volatility, marine apex predators
