Institution: California Institute of Technology
The first scientific description of dinosaurs was made nearly 170 years ago, but the ways in which they regulated their body temperatures remain a mystery. Dinosaurs could have been endotherms ("warm blooded") similar to birds and mammals, or might have been more similar to ectothermic ("cold blooded") reptiles such crocodiles and lizards, or perhaps depended on some intermediate metabolic strategy, such as "gigantothermy" the ability of some "cold blooded" animals to maintain high, stable body temperatures simply through great size. The PI will explore the body temperatures, and thereby the metabolisms, of dinosaurs using the most direct and quantitative measurements attempted to-date. He will use a novel geochemical approach, "clumped isotope" thermometry, which measures the temperature at which carbonate-bearing minerals, including carbonate-rich bio-apatite, formed based on the temperature-dependent ordering, or "clumping", of 13C and an 18O into bonds with each other. Initial results on modern and fossil mammals and well understood reptiles indicate this method can reconstruct the body temperature of an extinct species with an accuracy of 1-2oC. Our study will examine fossil remains of adult sauropod, theropod, and hadrosaur dinosaurs, co-existing crocodilians, as well as smaller juvenile and dwarf specimens of similar species. This project is expected to result in the first precise, quantitative measurements of dinosaur body temperatures; these data will have the potential to resolve one of the most long standing and well known debates in vertebrate paleontology. This project will be conducted with the help of undergraduate students from Caltech and a neighboring community college, and its results will be prepared for presentation to the broader public through the Los Angeles County Natural History Museum.
The nature of the dinosaurs — how they looked and behaved; their interactions with each other and their ecosystems — remains one of the great problems in natural history. Many questions about the dinosaurs concern their metabolisms — how their bodies generated energy, and how that in turn controlled their temperatures and overall levels of physical activity. Paleontologists have struggled for many years to reach clear conclusions about dinosaur metabolsim and body temperature because most of what we can observe — the distribution and physical properties of fossil bones and teeth — give few clues. The research supported by this grant aimed to make the first ever measurements of the body temperatures of extinct dinosaurs using a method that is quantitative, calibrated and relatively precise. The method in question examines the extenet to which rare isotopes of carbon and oxygen 'stick' to each other in the same carbonate chemcial unit within fossil mineral remains. It was demonstrated several years ago that this isotopic property is controlled by the temperature of mineral growth, and records temperature in a similar way, regardless of the mineral form or origin. We checked that the calibration of this tool applies to the teeth and egg shells of vertebrate animals by studying modern birds, reptiles, mammals and fish. We then studied the ancient fossil remains of animals with known metabolisms (e.g., pigs, mammoths, aligators) to prove we could observe the correct body temperatures in ancient materials from the rock record. Finally, we applied this tool to a suite of fossil teeth and egg shells from dinosaurs. Our findings indicate that dinosaur body temperatures varied by much more than do modern birds and mammals, extending from high values near the upper end of the range for living vertebrates, down to temperatures more typical of modern reptiles in warm climates. We found that body temperature is correlated with body size in dinosaurs, in a way that suggests their temperature was strongly influenced by 'giganthermy' — the propensity of large animals to retain body heat simply by virtue of their small surface areas realtive to their weights. This suggests that dinosaurs were not metabolically 'warm blooded' in the way that modern birds and mammals are. Rather, they were likely more closely similar to reptiles in their basal metabolisms but could have elevated body temperatures when they were large enough to retain heat efficiently. These results provide a new window into the basic physiology and behaviors of dinosaurs, and appear to disprove some wides spread current ideas. In particular, our findings suggest that recent arguments for 'warm bloodedness' of dinosaurs based on growth rates, bone vasculature and other arguments are misleading.
