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, 4 (11), e7783

Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs


Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs

Herman Pontzer et al. PLoS One.


Background: One of the great unresolved controversies in paleobiology is whether extinct dinosaurs were endothermic, ectothermic, or some combination thereof, and when endothermy first evolved in the lineage leading to birds. Although it is well established that high, sustained growth rates and, presumably, high activity levels are ancestral for dinosaurs and pterosaurs (clade Ornithodira), other independent lines of evidence for high metabolic rates, locomotor costs, or endothermy are needed. For example, some studies have suggested that, because large dinosaurs may have been homeothermic due to their size alone and could have had heat loss problems, ectothermy would be a more plausible metabolic strategy for such animals.

Methodology/principal findings: Here we describe two new biomechanical approaches for reconstructing the metabolic rate of 14 extinct bipedal dinosauriforms during walking and running. These methods, well validated for extant animals, indicate that during walking and slow running the metabolic rate of at least the larger extinct dinosaurs exceeded the maximum aerobic capabilities of modern ectotherms, falling instead within the range of modern birds and mammals. Estimated metabolic rates for smaller dinosaurs are more ambiguous, but generally approach or exceed the ectotherm boundary.

Conclusions/significance: Our results support the hypothesis that endothermy was widespread in at least larger non-avian dinosaurs. It was plausibly ancestral for all dinosauriforms (perhaps Ornithodira), but this is perhaps more strongly indicated by high growth rates than by locomotor costs. The polarity of the evolution of endothermy indicates that rapid growth, insulation, erect postures, and perhaps aerobic power predated advanced "avian" lung structure and high locomotor costs.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Schematic of extensor fascicle length (lfasc), the GRF vector moment arm (R; segmental gravitational, but not inertial, moments were also included but not shown here; see [48]), and the extensor (antigravity) muscle moment arm (r) for the hip joint.
These parameters were calculated at midstance for the antigravity muscle groups at the hip, knee, and ankle, and combined with step length (estimated from hip height) to estimate the volume of muscle activated per meter travelled (Vmusc); see Methods. Joint angles and position of the center of mass (yellow circle) are taken from Hutchinson . Adapted with permission from original artwork by Scott Hartman.
Figure 2
Figure 2
A. Locomotor power requirements for dinosauriforms (aeroic power, mlO2/s) plotted on a graph of maximum aerobic power (VO2max, mlO2/s), for extant endotherms (light red circles and shaded region) and ectotherms (blue circles and shaded region) versus body mass. Estimated rates of oxygen consumption for dinosauriforms are calculated using the two methods described in the text for walking (Froude 0.25), slow running (Froude 0.50), and moderate running (Froude 1.00) speeds (from left to right, Archaeopteryx, Marasuchus, Microraptor, Compsognathus, Lesothosaurus, Heterodontosaurus, Coelophysis, Velociraptor, Gorgosaurus, Dilophosaurus, Plateosaurus, Allosaurus, Tyrannosaurus). White symbols are estimates from hip height, black symbols are estimates from active muscle volume, Vmusc. The data points for Coelophysis and Velociraptor (both 20 kg) have been separated slightly for clarity. The upper limit of maximum aerobic power for modern ectotherms (i.e., the upper 95% confidence limit) is indicated by the upper boundary of the blue region; the upper limit for modern endotherms is indicated by the upper boundary of the red region. B. A similar plot as in A showing log10 residuals from the ectotherm trendline.
Figure 3
Figure 3. Evolution of locomotor cost and endothermy in Archosauria.
A. Estimates from our Vmusc-based method for slow walking (Fr 0.25) used to reconstruct the evolution of endothermy. Substantial size-related homoplasy is shown. B. Estimates from our hip height-based method for moderate running (Fr 1.0) as a less conservative alternative to Fig. 2A. Endothermy is estimated as ancestral for at least Dinosauriformes.

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