Book: The Dinosaur Heresies

Overview
Robert T. Bakker presents a forceful reinterpretation of dinosaurs that overturns the classic image of sluggish, cold-blooded reptiles. He argues that many dinosaurs were active, warm-blooded animals with high metabolic rates, complex behaviors, and anatomical specializations more akin to those of birds and mammals than to modern reptiles. The work synthesizes field observations, comparative anatomy, and emerging paleontological evidence to build a coherent alternative view of dinosaur physiology and ecology.

Core Arguments
Bakker contends that endothermy explains numerous features of dinosaur anatomy and distribution. Upright limb posture, rapid growth rates inferred from bone histology, and locomotive adaptations suggest sustained activity levels incompatible with ectothermy. He links metabolic demands to predator-prey ratios, community structure, and the ability of dinosaurs to inhabit diverse climates. The argument extends to physiology: respiratory efficiency, cardiovascular capacity, and insulation all play roles in a warm-blooded interpretation.

Evidence and Reasoning
The case rests on multiple converging lines of evidence. Bone microstructure and growth rings point to rapid growth and high metabolic throughput. Trackways and limb proportions indicate sustained locomotion rather than brief bursts of speed. Morphological features such as hollow bones, air sac-like structures, and erect posture are read as functional adaptations that parallel those of birds and certain mammals. Bakker emphasizes ecological data, arguing that population structures and faunal assemblages better match endothermic models.

Behavior and Ecology
Complex social behavior is a recurring theme. Bakker proposes parental care, pack hunting, herding, and territoriality, using fossil associations, nesting sites, and comparative analogies to living animals as supporting evidence. He interprets some skeletal and trackway patterns as signs of coordinated group behavior rather than chance aggregation. These behavioral inferences feed back into physiological claims: active social lifestyles and sustained activity are easier to reconcile with higher metabolic rates.

Controversy and Debate
The conclusions sparked vigorous debate. Critics questioned whether the available data could unambiguously demonstrate endothermy or specific behaviors, and many pointed to alternative explanations tied to reptilian physiology or environmental effects. Methodological disputes arose over how to interpret bone histology, trackway evidence, and ecological inferences. The provocative tone and sweeping claims drew both strong support from proponents of the emerging Dinosaur Renaissance and skepticism from those favoring more conservative reconstructions.

Legacy
The reinterpretation accelerated a shift in paleontological thinking and in popular perception of dinosaurs. Subsequent discoveries, including feathered theropods, more detailed growth studies, and refined analyses of respiratory anatomy, provided additional context that validated several of Bakker's predictions even as other details were revised. The work helped catalyze a research agenda that treats dinosaurs as dynamic, physiologically complex organisms rather than static, reptilian backdrops, influencing both scientific inquiry and public imagination.