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New in PLoS ONE: Running Biomechanics and Endothermy in Dinosaurs
Pontzer H, Allen V, Hutchinson JR (2009) Biomechanics of Running
Indicates Endothermy in Bipedal Dinosaurs. PLoS ONE 4(11): e7783.
Freely available at:
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.
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.
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.