Dinosaurian Biology

Were the dinosaurs cold or warm blooded?????

These pages are maintained by Tamsin Rothery - e-mail tr7401@bris.ac.uk

Before you start

On these pages warm-bloodedness will mean endothermy and cold-bloodedness will mean ectothermy

Any links followed by (gl) will take you to the glossary.

Introduction

The name dinosaurs, given by Richard Owen in 1842, means terrible lizards. This name was give because the bones in dinosaurs' skeletons are more similar to those of lizards than to those of mammals and, indeed, we think dinosaurs are more closely related to lizards than to mammals.

Click here for more information on dinosaur relationships

Because of this relationship it was initially thought that dinosaurs' bodies would work in a very similar way to lizards' bodies - that is, that they would be cold-blooded.

Click here for an early reconstruction of some dinosaurs

However, there are many lines of evidence that seem to indicate that the dinosaurs were warm-blooded and some people think they had a completely different system of temperature control.

Firstly, we should consider what the advantages and disadvantages of being warm or cold-blooded are.

Warm-blooded animals have to eat large amounts of food in order to provide energy and produce heat. Cold-blooded animals do not need to generate heat and so can eat a lot less.
For example, a cheetah weighing 50-60kg will eat its own weight every 10 days. Whereas a komodo dragon, a large reptile, weighing 50kg will eat its own body weight every 60 days.
Warm-blooded animals are capable of being active for long periods of time - this is because a lot of energy is produced by all the food they eat (as well as heat). Cold-blooded animals can only cope with short amounts of activity, they then have to rest.
Warm-blooded animals need to drink a lot of water. This is because they loose water when they sweat or pant (water vapour lost) to keep cool. As warm-blooded creatures are highly active, they make a lot of heat by muscle contraction and also produce heat constantly, even when stationary. This makes cooling mechanisms are especially important. Cold-blooded creatures do not loose water to keep cool. They cannot sweat as they have impermeable (gl) skin. However, they do not really need these additional cooling mechanisms as they are not as active as warm-blooded creatures and can cool down by moving into the shade.
The constant temperatures achieved by warm-blooded creatures means that their enzymes can work at maximum efficiency. This means it is 'safe' for them to develop more complex functions as the environment is relatively steady. Because of the fluctuating temperatures of cold-blooded creatures, their enzymes have to cope with extreme conditions and therefore find it harder to develop.

Opinion is divided on the subject, so read the evidence listed below and make up your own mind!

Bone Histology

Birds as Dinosaurs

Oxygen Isotopes

Predator/Prey Ratios

Dinosaur Physiology

Where Dinosaurs Lived

Gigantothermy - What is it?

Further Reading

Robert Bakker - The Dinosaur Heresies

Dr. Bakker is the main spokesperson for the warm-blooded dinosaur idea. Very easy to follow.

Adrian J. Desmond - The Hot-Blooded Dinosaurs

An easy to read, historical look at how ideas on dinosaurian biology have developed.

Ed.s R.D.K. Thomas and E.C. Olson - A Cold Look at the Warm-Blooded Dinosaurs

This collection of scientific papers (including one by Bakker) provides a more objective overview on the subject. As it was written for a scientific audience, a lot of knowledge is assumed and some of the terminology may be hard to follow.