Prehistoric Animals


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Dinosaurs blood

Warm or cold-blooded?

Until recently, it was generally accepted that dinosaurs, like modern reptiles, were cold-blooded animals. Recent research has casted a shadow of doubt on this hypothesis. One of the most controversial questions scientists have been asking themselves about dinosaurs in recent times is whether they were cold-blooded creatures, as they have been thought to be for a long time, or warm-blooded. This debate has raised important questions about the physiology of dinosaurs. We may never find the answer, for the simple reason that body temperature, unlike bones, does not fossilize. We can nevertheless make certain deductions by studying the data provided by the fossils and by using our knowledge of living creatures. In reality, the question is not whether dinosaurs were warm or cold blooded, because these terms are misleading. In warm weather, for example, blood temperature may be higher in cold-blooded animals such as crocodiles than in warm-blooded mammals of the same size. The real question is: were dinosaurs able to maintain a constant internal temperature, such as birds and mammals, or did their internal temperature fluctuate according to their environment, such as lizards, snakes? and crocodiles? Homeothermy has advantages and disadvantages. The main advantage for the animal is that it is always ready to act, day or night, in hot weather or in cold weather. This means that it is able to exploit its habitat and endure conditions (such as night temperatures close to 0) that would not support a variable temperature animal. The main disadvantage of homeothermy is that it consumes a lot of energy and thus the animal must eat more. A lion who is homeothermic, and therefore warm-blooded, must eat as example about ten times more than an endothermic crocodile, and therefore cold-blooded, of the same size. There is some evidence that dinosaurs had a variable physiology: some were warm-blooded and others were cold-blooded.


Troodon formosus
Troodon formosus

The fact that theropods were the ancestors of birds, warm-blooded animals, allowed some researchers to think they were also warm-blooded. In addition, recent discoveries in China have shown that small theropods had a hair cover or even feathers that would help them not to cool. Smaller theropods weighing less than 100 kg should be able to remain active to hunt. Some of them, such as dromaeosaurids and troodontids, had sharp claws, which are usually more associated with warm-blooded creatures than cold-blooded, low-energy creatures. Another argument: the discovery of small theropods and ornithopods in high-latitude areas such as the Dinosaur Cove in Victoria, Australia, where the temperatures of the Mesozoic winter fell below 0 C. Today, this kind of environment is the field of warm-blooded animals. But perhaps it is not appropriate to establish analogies between the present and the past. Remnants of other Cretaceous cold-blooded animals such as crocodiles and large amphibians have also been found at these sites.

Comparison with crocodiles


Recent studies on the internal temperature of crocodiles may be able to solve the problem of thermal regulation in large dinosaurs. The internal temperature of crocodiles decreases more slowly as they grow. In other words, the growing mass of the animal serves to conserve heat inside the body. A specimen of 5 tons would therefore have a constant internal temperature simply because it is bigger. If such a system applied to dinosaurs, the larger ones would have been forced to evacuate the heat provided by the outside or generated by movement and digestion. Long necks and long tails may have played a role in increasing the area relative to the animal's mass. Plates, tips and wings may also have contributed to the regulation of the internal temperature. This would explain the function of the plates of stegosaurs or sails of Spinosaurus and Ouranosaurus.