Dinosaurian digestive strategies indicated by gastrolith shapes (free pdf)
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Ben Creisler
Jul 20, 2026, 1:13:55 PM (3 days ago) Jul 20
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Ben Creisler
A new paper:
Ryuji Takasaki, Yoshitsugu Kobayashi, Anthony R. Fiorillo, Tsogtbaatar Chinzorig & Gregory F. Funston (2026)
Gastrolith shape as an indicator of digestive function and its implications for dinosaurian digestive strategies
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2026.10112
https://www.cambridge.org/core/journals/paleobiology/article/gastrolith-shape-as-an-indicator-of-digestive-function-and-its-implications-for-dinosaurian-digestive-strategies/647E287A6C4E48CF4C50C709BE917BC7
The evolution of the muscular stomach was a key innovation in the avian body plan, enabling high metabolic rates by functionally replacing oral processing. However, its deep-time origins within Archosauria have remained poorly understood, primarily due to the extreme rarity of fossilized stomachs. Here, we demonstrate that gastrolith shape is a robust proxy for digestive function and, by extension, stomach muscularity and diet. By assembling a comprehensive dataset from 104 individuals across 46 extant archosaur species, we establish a strong correlation between gastrolith shape, stomach muscularity, and diet. Application of this validated method to the fossil record reveals divergent digestive strategies among major dinosaur clades. Herbivorous ornithischians retained angular gastroliths, consistent with limited gastric abrasion and compensation through oral processing. Sauropods likewise retained angular gastroliths, consistent with limited gastric abrasion and digestion relying more on long retention times and fermentation. Conversely, the muscular stomach, indicated by rounded gastroliths, evolved early within Theropoda, appearing at least by the base of Maniraptoriformes. This innovation was likely a crucial prerequisite for repeated transitions to herbivory in maniraptoriform theropods with reduced dentition, shifting mechanical processing from the jaws to the stomach and reducing reliance on heavy jaw adductor musculature.
Non-technical Summary
For decades, paleontologists have often interpreted the discovery of stomach stones, or gastroliths, inside a dinosaur’s ribcage as a sign of a plant-based diet. However, because many modern carnivores also swallow stones, this assumption has been uncertain. This study reveals that the secret to understanding a dinosaur’s digestion lies not in the presence of stones, but in their shape. Analysis of a new, comprehensive dataset from modern birds and crocodiles shows that rounded stones are a clear indicator of a muscular stomach used to grind tough, fibrous plants. Angular stones, in contrast, point to a weaker stomach and reduced gastric processing. Applying this new lens to the fossil record reveals a major evolutionary divergence. Iconic herbivores like the distant relatives of Triceratops retained angular stones, consistent with limited gastric abrasion and reliance on chewing and other processing. Long-necked sauropods also retained angular stones, suggesting limited gastric abrasion. Their digestion likely relied more on retention time and fermentation rather than a powerful grinding stomach. In contrast, the lineage of meat-eating dinosaurs that led to birds evolved muscular gizzards early in their history. This key innovation allowed them to process tough foods without relying on heavy jaw musculature, paving the way for subsequent skull and feeding adaptations in the avian stem lineage.
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Free pdf:
Ryuji Takasaki, Yoshitsugu Kobayashi, Anthony R. Fiorillo, Tsogtbaatar Chinzorig & Gregory F. Funston (2026)
Gastrolith shape as an indicator of digestive function and its implications for dinosaurian digestive strategies
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2026.10112
https://www.cambridge.org/core/journals/paleobiology/article/gastrolith-shape-as-an-indicator-of-digestive-function-and-its-implications-for-dinosaurian-digestive-strategies/647E287A6C4E48CF4C50C709BE917BC7
The evolution of the muscular stomach was a key innovation in the avian body plan, enabling high metabolic rates by functionally replacing oral processing. However, its deep-time origins within Archosauria have remained poorly understood, primarily due to the extreme rarity of fossilized stomachs. Here, we demonstrate that gastrolith shape is a robust proxy for digestive function and, by extension, stomach muscularity and diet. By assembling a comprehensive dataset from 104 individuals across 46 extant archosaur species, we establish a strong correlation between gastrolith shape, stomach muscularity, and diet. Application of this validated method to the fossil record reveals divergent digestive strategies among major dinosaur clades. Herbivorous ornithischians retained angular gastroliths, consistent with limited gastric abrasion and compensation through oral processing. Sauropods likewise retained angular gastroliths, consistent with limited gastric abrasion and digestion relying more on long retention times and fermentation. Conversely, the muscular stomach, indicated by rounded gastroliths, evolved early within Theropoda, appearing at least by the base of Maniraptoriformes. This innovation was likely a crucial prerequisite for repeated transitions to herbivory in maniraptoriform theropods with reduced dentition, shifting mechanical processing from the jaws to the stomach and reducing reliance on heavy jaw adductor musculature.
Non-technical Summary
For decades, paleontologists have often interpreted the discovery of stomach stones, or gastroliths, inside a dinosaur’s ribcage as a sign of a plant-based diet. However, because many modern carnivores also swallow stones, this assumption has been uncertain. This study reveals that the secret to understanding a dinosaur’s digestion lies not in the presence of stones, but in their shape. Analysis of a new, comprehensive dataset from modern birds and crocodiles shows that rounded stones are a clear indicator of a muscular stomach used to grind tough, fibrous plants. Angular stones, in contrast, point to a weaker stomach and reduced gastric processing. Applying this new lens to the fossil record reveals a major evolutionary divergence. Iconic herbivores like the distant relatives of Triceratops retained angular stones, consistent with limited gastric abrasion and reliance on chewing and other processing. Long-necked sauropods also retained angular stones, suggesting limited gastric abrasion. Their digestion likely relied more on retention time and fermentation rather than a powerful grinding stomach. In contrast, the lineage of meat-eating dinosaurs that led to birds evolved muscular gizzards early in their history. This key innovation allowed them to process tough foods without relying on heavy jaw musculature, paving the way for subsequent skull and feeding adaptations in the avian stem lineage.
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