Isotopologue thermometry of fossil hard tissues: A new approach to inferring dinosaur body temperature.
Zusammenfassung der Projektergebnisse
The clumped isotope analysis is a relativly new method in isotope geochemistry for high precision measurements of the 13C-18O bond abundance in carbonate minerals to determine the (bio-)mineral formation temperature. This chemical thermometer measures how often the heavy rare isotopes 13C and 18O clump together to form 13C-18O-bonds in carbonate molecules. From theoretical considerations this also should apply to the carbonate moiety in biogenic apatite of enamel and calcium carbonate of eggshells. Aim of this research project was to develop the clumped isotope thermometer for skeletal bioapatite of vertebrates. For this purpose enamel of modern vertebrates (sharks, crocodiles, mammals) with well-known body temperatures in the range from 23° to 37°C were analyzed. This empirical calibration was then used to determine dinosaur body temperatures, especially of sauropds, the largest land animals on Earth. This required defining criteria to verify the preservation of original 13C-18O bond abundance and thus body temperature information in fossil hard tissues. A combination of different histological, mineralogical and geochemical indicators was developed and applied for this purpose. Clumped isotope analysis of enamel from Late Pleistocene mammoth yielded the same body temperature as that of a modern Indian elephant. Similar temperatures of 36- 38°C were determined for well-preserved enamel of giant Late Jurassic sauropods such as Camarasaurus and Brachiosaurus. Temperatures were also determined for dinosaur eggshells for which the egg-laying taxon could be inferred either by in situ embryos or associated skeletal remains. The eggshell formation temperature reflects the core body temperature of sexually mature, egg-laying female dinosaurs. For two Cretaceous dinosaurs, a sauropod titanosaur (38°C) and the theropod Oviraptor (32°C) different eggshell formation temperatures were determined. The Oviraptor had a body temperature of only 32°C, which, however, was significantly higher than the Late Cretaceous ambient air temperature. Although birds evolved from theropod dinosaurs Oviraptor had a different thermophysiology than extant birds, which mostly have body temperatures well above 40°C. Overall, our temperature reconstructions demonstrate that dinosaurs had different thermoregulation strategies. Some had mammal-like body temperatures and were possibly warm-blooded. Ongoing investigations on small-bodied dinosaurs, such as dwarf sauropods, will provide more detailed information in this regard. Our results clearly demonstrate that clumped isotope analysis of fossil tooth enamel and egggshells enables us to reconstruct the body temperature of extinct vertebrates. This opens new research avenues to assess the evolution of endothermy among vertebrates and the ambient climatic conditions for cold blooded taxa.
Projektbezogene Publikationen (Auswahl)
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(2010): Body temperatures of modern and extinct vertebrates from 13C-18O bond abundances in bioapatite. Proceedings of the National Academy of Sciences 107, 10377-10382
Eagle, R.A., Schauble, E.A., Tripati, A.K., Tütken, T., Hulbert, R.C. & Eiler, J.M.
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2011. Direct measurement of dinosaur body temperatures from the analysis of isotopic (13C-18O) ordering in fossil biominerals. Science 333, 443-445
Eagle, R.A., Tütken, T., Martin, T.S., Tripati, A.K., Fricke, H.C., Connely, M., Cifelli, R.L., Eiler, J.M.
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2014. Empirical calibration of the clumped isotope paleothermometer using calcites of various origins. Geochimica et Cosmochimica Acta 141, 127-144
Wacker, U., Fiebig, J., Schöne, B.R., Bahr, A., Friedrich, O., Tütken, T., Gischler, E. & Joachimski, M.M.
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Isotopic ordering in eggshells reflects body temperatures and suggests differing thermophysiology in two Cretaceous dinosaurs. Nature Communications volume 6, Article number: 8296 (2015)
Eagle, R.A., Enriquez, M., Grellet-Tinner, G., Hu, D., Pérez-Huerta, A., Tütken, T., Montanari, S., Loyd, S.J., Ramirez, P., Tripati, A.K., Kohn, M.J., Cerling, THE, Chiappe, L.M. & Eiler, J.M.
