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, 4 (8), e248

Dinosaur Fossils Predict Body Temperatures

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Dinosaur Fossils Predict Body Temperatures

James F Gillooly et al. PLoS Biol.

Abstract

Perhaps the greatest mystery surrounding dinosaurs concerns whether they were endotherms, ectotherms, or some unique intermediate form. Here we present a model that yields estimates of dinosaur body temperature based on ontogenetic growth trajectories obtained from fossil bones. The model predicts that dinosaur body temperatures increased with body mass from approximately 25 degrees C at 12 kg to approximately 41 degrees C at 13,000 kg. The model also successfully predicts observed increases in body temperature with body mass for extant crocodiles. These results provide direct evidence that dinosaurs were reptiles that exhibited inertial homeothermy.

Figures

Figure 1
Figure 1. A Plot of the Relationship between Average Body Temperature (°C) and the Logarithm of Body Mass for Dinosaurs and Extant Crocodiles
For dinosaurs, body temperatures were estimated from Equation 2 using data on ontogenetic growth trajectories determined from bone histology (see Materials and Methods). Body mass is expressed as the size at which maximum growth rates occur, which is about half of asymptotic adult size. The fitted line includes the following species in ascending order of weight: P. mongoliensis (12 kg), M. carinatus (140 kg), Al. sarcophagus (614 kg), G. libratus (622 kg) , D. torosus (869 kg), T. rex (2,780 kg), and Ap. excelsus (12,979 kg) [ – 11]. The line was fit to the data using non-linear least squares regression in order to generate predictions on the change in body temperature with body mass for crocodiles ( Figure 2). This line does not include the two additional species shown here, the dinosaur bird Sh. deserti (1 kg), which was not considered because it was feathered, and Sy. rhodesiensis (11 kg), which was excluded because it was an outlier (see text). For crocodiles, body temperature estimates are based on the previously observed relative increase in body temperature with body size for individuals (32–1,010 kg) held under natural conditions, and by assuming a mean annual environmental temperature of 25 °C [ 5].
Figure 2
Figure 2. A Plot of the Observed versus the Predicted Increase in Average Body Temperature (°C) with Body Mass for Crocodiles
The observed increase in average body temperature for crocodiles ranging in mass from 32–1,010 kg [ 5] was plotted versus the predicted increase in average body temperature with body mass for these crocodiles based on the line fit to the dinosaur data shown in Figure 1 and predicted from Equation 2.

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