GEOL 104 Dinosaurs: A Natural History

Fall Semester 2006
Hot- or Cold-Running Dinosaurs?

Among modern vertebrates, some gross generalizations:
Birds and mammals are warm-blooded; Crocodilians, lepidosaurs, turtles, amphibians, and most fish are cold-blooded.

Old debate in dinosaur studies: were they warm-blooded or cold-blooded?

Owen in 1842 suggested dinosaurs might have been warm-blooded, or at least more warm-blooded than typical modern reptiles.

Need to be precise as to definitions of terms.
"Warm-blooded" and "Cold-blooded" actually encompass several different (although related) topics:

A typical cold-blooded animal is an ectothermic bradymetabolic poikilotherm: needs to get its energy from the sun and fluctuates with external environment (but can moderate fluctuations by moving from sunlight to shade and vice versa); however, needs very little food (snakes can go weeks without feeding, for example). Cold blooded animals become torpid at night and in colder weather.

A typical warm-blooded animal is an endothermic tachymetabolic homeotherm: its body temperature is stable and activity levels can remain high for long periods of time, at night, and in colder weather; however, needs a LOT of food or will die (imagine the effects of not feeding a cat or dog for weeks…).

How can people determine the thermal physiology of extinct animals like non-avian dinosaurs?

Owen suggested dinosaurs might have been warm-blooded because:

Many late 19th Century paleontologists considered dinosaurs to be more similar to modern warm-blooded animals in terms of activity levels.

During early 20th Century, shift to lizard-like concept for dinosaurs.

Concept of warm-blooded dinosaurs revived in late 1960s by Ostrom because of a number of lines of evidence:

Colleague from France: Armand de Ricqlès added additional line of evidence:

Ostrom's undergrad student Robert T. Bakker: main advocate for the "hot-blooded" dinosaurs model. Added his own observations:

Additional lines of evidence (primarily from 1980s and 1990s):

Not everyone convinced that dinosaurs were fully endothermic tachymetabolic homeotherms.

Two main types of evidence to the contrary:

Lines of evidence supporting dinosaurian ectothermy:

To Next Lecture.
To Previous Lecture.
To Syllabus.

Last modified: 14 July 2006