Caiuajara (pterosaur) metabolic rate and aerobic capacity (free pdf)
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Ben Creisler
Sep 2, 2026, 1:59:47 PMSep 2
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Ben Creisler
A new paper:
Studies on paleophysiology and thermoregulation are central topics in fossil vertebrate paleobiology because they allow inferences about extinct organismal function beyond anatomical description. Pterosaur thermophysiology remains actively debated. Evidence such as relatively rapid growth and elevated metabolic rate estimates has been used to argue for endothermic-like physiologies consistent with the energetic demands of powered flight, whereas reproductive traits, including burial incubation and precocial development, have led some authors to propose ectothermic strategies more akin to those of extant non-avian diapsids. Here, we provide quantitative estimates of resting metabolic rate (RMR) for the tapejarid pterosaur Caiuajara dobruskii using phylogenetic eigenvector maps and osteocyte lacunar density as proxy. Analysis of six histological sections from three appendicular elements (femur, tibia, humerus) at different ontogenetic stages (adult and juvenile) yielded mass-independent RMR estimates of 0.24–0.76 ml O2 h−1 g−0.86, substantially higher than those of lepidosaurs but lower than typical mammalian and avian values. The retrodicted mass-independent maximum metabolic rate (MMR) of 5.68 ml O2 h−1 g−0.87 falls between values for highly active reptiles and birds, suggesting sufficient aerobic capacity to sustain powered flight without fully matching the maximal performance of small endotherms. Together, these results suggest active-flighted pterosaurs fall among a metabolically intermediate continuum, limiting straightforward actualistic comparisons for inferring their thermoregulatory strategy.
Non-technical Summary
Pterosaurs were flying reptiles that lived alongside dinosaurs and were the first vertebrates to achieve powered flight. How they produced and regulated the heat and energy needed for this lifestyle has been debated for decades, with proposals ranging from reptile-like “cold-blooded” physiology to bird-like “warm-blooded” systems. In this study, bones of the pterosaur Caiuajara dobruskii from both juvenile and adult individuals were examined under the microscope. The analysis focused on tiny cavities in the bone that once housed bone cells. The density of these spaces can be used to estimate how rapidly an animal grows, consumes oxygen and, therefore, its metabolic intensity. The results show that Caiuajara probably had higher metabolic rates than those of most living reptiles, but not as extreme as those of typical mammals and birds, placing it in an intermediate metabolic continuum. Despite this intermediate metabolism, Caiuajara could sustain energetically demanding behaviors, including powered flight, while maintaining a level of internal heat production greater than that of most modern reptiles, though not as intense as in small warm-blooded animals.
Free pdf:
Esaú Victor de Araújo, Mariana Valeria Haase, Jorge Cubo, Luiz Carlos Weinschütz, Alexander Wilhelm Armin Kellner & Juliana Manso Sayão (2026)
New insights on metabolic rates and aerobic scopes of the tapejarid pterosaur Caiuajara dobruskii
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2026.10111
https://www.cambridge.org/core/journals/paleobiology/article/new-insights-on-metabolic-rates-and-aerobic-scopes-of-the-tapejarid-pterosaur-caiuajara-dobruskii/FFCA9092D493066EAD69332652DCCB9A
Abstract
Esaú Victor de Araújo, Mariana Valeria Haase, Jorge Cubo, Luiz Carlos Weinschütz, Alexander Wilhelm Armin Kellner & Juliana Manso Sayão (2026)
New insights on metabolic rates and aerobic scopes of the tapejarid pterosaur Caiuajara dobruskii
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2026.10111
https://www.cambridge.org/core/journals/paleobiology/article/new-insights-on-metabolic-rates-and-aerobic-scopes-of-the-tapejarid-pterosaur-caiuajara-dobruskii/FFCA9092D493066EAD69332652DCCB9A
Abstract
Studies on paleophysiology and thermoregulation are central topics in fossil vertebrate paleobiology because they allow inferences about extinct organismal function beyond anatomical description. Pterosaur thermophysiology remains actively debated. Evidence such as relatively rapid growth and elevated metabolic rate estimates has been used to argue for endothermic-like physiologies consistent with the energetic demands of powered flight, whereas reproductive traits, including burial incubation and precocial development, have led some authors to propose ectothermic strategies more akin to those of extant non-avian diapsids. Here, we provide quantitative estimates of resting metabolic rate (RMR) for the tapejarid pterosaur Caiuajara dobruskii using phylogenetic eigenvector maps and osteocyte lacunar density as proxy. Analysis of six histological sections from three appendicular elements (femur, tibia, humerus) at different ontogenetic stages (adult and juvenile) yielded mass-independent RMR estimates of 0.24–0.76 ml O2 h−1 g−0.86, substantially higher than those of lepidosaurs but lower than typical mammalian and avian values. The retrodicted mass-independent maximum metabolic rate (MMR) of 5.68 ml O2 h−1 g−0.87 falls between values for highly active reptiles and birds, suggesting sufficient aerobic capacity to sustain powered flight without fully matching the maximal performance of small endotherms. Together, these results suggest active-flighted pterosaurs fall among a metabolically intermediate continuum, limiting straightforward actualistic comparisons for inferring their thermoregulatory strategy.
Non-technical Summary
Pterosaurs were flying reptiles that lived alongside dinosaurs and were the first vertebrates to achieve powered flight. How they produced and regulated the heat and energy needed for this lifestyle has been debated for decades, with proposals ranging from reptile-like “cold-blooded” physiology to bird-like “warm-blooded” systems. In this study, bones of the pterosaur Caiuajara dobruskii from both juvenile and adult individuals were examined under the microscope. The analysis focused on tiny cavities in the bone that once housed bone cells. The density of these spaces can be used to estimate how rapidly an animal grows, consumes oxygen and, therefore, its metabolic intensity. The results show that Caiuajara probably had higher metabolic rates than those of most living reptiles, but not as extreme as those of typical mammals and birds, placing it in an intermediate metabolic continuum. Despite this intermediate metabolism, Caiuajara could sustain energetically demanding behaviors, including powered flight, while maintaining a level of internal heat production greater than that of most modern reptiles, though not as intense as in small warm-blooded animals.
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