Dinosaur energetics: setting the bounds on feasible physiologies and ecologies
TL;DR: Quantitative analysis of dinosaur energetics shows that many features of dinosaur lifestyle are compatible with a physiology similar to that of extant lizards, scaled up to dinosaur body masses and temperatures.
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Abstract: The metabolic status of dinosaurs has long been debated but remains unresolved as no consistent picture has emerged from a range of anatomical and isotopic evidence. Quantitative analysis of dinosaur energetics, based on general principles applicable to all vertebrates, shows that many features of dinosaur lifestyle are compatible with a physiology similar to that of extant lizards, scaled up to dinosaur body masses and temperatures. The analysis suggests that sufficient metabolic scope would have been available to support observed dinosaur growth rates and allow considerable locomotor activity, perhaps even migration. Since at least one dinosaur lineage evolved true endothermy, this study emphasizes there was no single dinosaur physiology. Many small theropods were insulated with feathers and appear to have been partial or full endotherms. Uninsulated small taxa, and all juveniles, presumably would have been ectothermic, with consequent diurnal and seasonal variations in body temperature. In larger taxa, inertial homeothermy would have resulted in warm and stable body temperatures but with a basal metabolism significantly below that of extant mammals or birds of the same size. It would appear that dinosaurs exhibited a range of metabolic levels to match the broad spectrum of ecological niches they occupied.
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Figure 2. Growth rates in dinosaurs. A. Relationship between estimated maximum annual growth rate (kg y -1 ) in dinosaurs and adult (asymptotic) body mass (kg) (black symbols and fitted line). The scaling exponent is 0.75 (SE 0.07). Data for growth rate averaged over the lifespan shown for four taxa (grey symbols, not included in fitted relationship). Data for Apatasaurus and Maiasaura from Erickson et al. (2001) and Chasmosaurus from Lehman (2007) are shown as white symbols, and not included in the fitted relationship. B. Comparison of daily growth rate in mammals (white symbols), reptiles (grey symbols) and dinosaurs (black symbols). Reptile and mammal data are from Case (1978a); dinosaur data assume aseasonal growth. Lines show least-squares linear regressions fitted with a General Linear Model; the common slope is 0.71 (SE 0.02). 
Figure 4. A. Turnover number (fraction of body energy consumed per day) for dinosaurs modelled as ectotherms (solid and dashed lines) and endotherms (Tb 37.5 o C, dotted line). The ectotherm lines are modelled estimates for a herbivore (dashed line) and an active predator (solid line); in each case data are shown for Tb 25 o C (lower) and 35 o C (upper). B. Relationship between daily travel distance (km) and body mass (g) in dinosaurs; presentation as for A. Also shown (dotted line) is the diameter of core home range extrapolated from data for living lizards (Christian and Waldschmidt 1984), assuming core range is 25% estimated home range (Stone and Baird 2002). 
Figure 5. Reproductive output in dinosaurs. A. Scaling relationship between annual reproductive output in oviparous (black symbols and regression line) and viviparous lizards (white symbols) (data from Meiri et al. 2012). Also shown are estimates for dinosaurs from Varricchio et al. (2008) (grey symbols). B. Growth model for Tyrannosaurus rex (Erickson et al. 2004): body mass (black symbols) and annual growth rate (kg y -1 , white symbols) as a function of age. Also shown is an estimate of annual reproductive output (g y -1 , grey symbols). The bar shows the range of estimates of the timing of the onset of sexual maturity from Schweitzer et al. (2005) and Lee and Werning (2008). 
Figure 1. A. Basal metabolic rate (BMR, W) as a function of body mass (g) in reptiles (black symbols), extrapolated to the body mass values of dinosaurs (plotted range 3 g to 65 tonnes), and compared with mammals (open symbols, plotted range 3 g to 1.2 tonnes). The reptile relationships are for Tb of 15 o C (lower) and 35 o C (higher), and the mammal relationship for 37.5 o C. B. Boxplots of factorial aerobic scope (FMR/BMR) for terrestrial vertebrates. Data for endotherms are shown in grey, and ectotherms in white. Plots show median with 25th and 75th percentiles (box), together with 10th and 90th percentiles (whiskers) and individual outliers (dots). Data from Nagy (2005) and Clarke and Pörtner (2010). 
Figure 3. A. Thermodynamic cost of growth (fraction of the absolute metabolic scope) as a function of body mass (Mb, g) in dinosaurs. The lines are model estimates for a herbivore with Tb 25 o C (upper) and an active predator with Tb 35 o C (lower). Individual data points are for those dinosaurs for which we have estimates of annual growth rate. B. Frequency histograms of cost of growth as a fraction of metabolic scope for reptiles (Tb 25 o C, white bars) and dinosaurs (Tb 35 o C, grey bars). The skewness is caused by back-transformation from scaling relationships based on logarithmically transformed variables. Also shown are the geometric mean and range for reptilian data with Tb of 25 o C (lower white symbol) and 35 o C (upper white symbol) and for dinosaurs with Tb 35 o C (grey symbol).
Citations
Reconstructing the mass and thermal ecology of North American Pleistocene tortoises
TL;DR: In this paper, the authors provided new metrics to derive quantitative weight estimates from measurements of the tortoise shell and found that the regression between straight carapace length and weight is most significant, with a maximum r2 > 0.99.
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150 million years of sustained increase in pterosaur flight efficiency
TL;DR: Novel phylogenetic statistical methods and biophysical models combined with information from the fossil record mean the opportunity to test hypotheses about evolutionary changes to the energetics of locomotion following the transition to flight is available.
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Evidence of endothermy in the extinct macropredatory osteichthyan Xiphactinus audax (Teleostei, Ichthyodectiformes)
TL;DR: This study presents an equivalent methodology developed for assessing locomotion energetics in extinct osteichthyans and provides evidence of endothermy in X. audax.
Response to formal comment on Myhrvold (2016) submitted by Griebeler and Werner (2017).
TL;DR: A formal comment on Myhrvold, 2016 defends the conclusions of Werner and Griebeler, 2014, and shows that the comparison with dinosaurs must be restricted only to extant sauropsids, ignoring other vertebrate groups, is unsupported by established principles of phylogenetic comparison.
Early Jurassic origin of avian endothermy and thermophysiological diversity in dinosaurs
Alfio Alessandro Chiarenza,Juan L. Cantalapiedra,Lewis A. Jones,Sara Gamboa,Sofía Galván,Alexander J. Farnsworth,Paul J. Valdes,Graciela Sotelo,Sara Varela +8 more
TL;DR: This study investigates the origin of avian endothermy and thermophysiological diversity in dinosaurs, revealing distinct evolutionary pathways in ornithischians and theropods, with theropods adopting endothermy in the Early Jurassic, while sauropodomorphs remained poikilothermic.
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