The Warm and Cold Blooded Nature of Dinosaurs
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The debate of whether dinosaurs were cold blooded or warm blooded has been ongoing since the beginning of the century. At the turn of the century scientists believed that dinosaurs had long limbs and were fairly slim, supporting the idea of a cold blooded reptile. Recently, however, the bone structure, number or predators to prey, and limb position have suggested a warm blooded species. In addition, the recent discovery of a fossilized dinosaur heart has supported the idea that dinosaurs were a warm blooded species. In this essay, I am going to give supporting evidence of dinosaurs being both warm and cold blooded. I will provide background information on the dinosaur that was discovered and what information it provides scientists.
Until recently, scientists believed the chances of finding a fossilized dinosaur heart were extremely slim. The heart belonged to a 66 million year old dinosaur found in Harding County in Northwestern South Dakota. The dinosaur, found in 1993, weighed over 650 pounds and was 13 feet long. The dinosaur was in fairly good condition with the exception of the left side of the skeleton. The small, plant-eating Thescelosaurus, nicknamed ‘Willo’ has been acquired by the North Carolina Museum of Natural Sciences. Thescelosaurus was an ornithischian, or "bird-hipped," dinosaur that lived in the latter stage of the Cretaceous period. This was approximately 1 million years before the end of the dinosaur era. Native to North America, its range extended from the northern United States up into Canada. Since using the 3-D software to reveal Willo's heart, scientists have also used it to create 3-D images of the fossil's skull, and of remains from other dinosaurs in the museum's collection. (Fisher, Paul)
A group of scientists from North Carolina and Oregon used medical technology to search an iron-stained concretion inside the specimen’s chest. With the assistance of imaging equipment and software, they were able to reconstruct 3-dimensional structures through the interior of the concretion. The images reveal a heart that was more like that of a bird or a mammal than those of reptiles, significantly adding to evidence suggesting that at least some dinosaurs had high metabolic rates. In addition, the heart appears to have been four chambered with a single aorta, which is most commonly found in mammals or birds.
This seems to indicate a high level of activity in at least this species of dinosaur. These discoveries to do not prove, without doubt, that this dinosaur was a warm blooded animal. However, these findings add some evidence to the argument of warm or cold blooded dinosaurs. (Fisher, Paul)
Ectothermy is the definition of a cold blooded animal that keeps its body warm by using heat from outside of the body. This means that the animal is heated externally. The main sources for this heat are the sun and the air around the body. Ectotherms lie in the sun to warm their bodies so that they can function properly. Modern ectotherms include crocodiles, alligators and lizards. Ectothermy has contributed to the ongoing success of the arthropods, fish, reptiles, and all modern animals with the exception of mammals and birds. Another term for Ectotherms is poikilotherms. Poikilotherms have a fluctuating internal body temperature that is dependent on surrounding environmental conditions. There body temperature can range form very high to very low. Ectothermy is sometimes perceived as being in some way inferior to endothermy, warm blooded, but in reality it is a sensible and efficient way of maintaining body temperature. Ectothermy is very energy efficient and require substantially less calories than endotherms. Some evidences supporting the idea that dinosaurs were ectotherms include: When dinosaurs lived, the climate was very warm. Therefore, the dinosaurs had no need to be endothermic because it was always warm enough outside. Fossilized skin impressions show that many of the dinosaurs had somewhat scaly skin. Most modern ectotherms have scaly skin as well. These pieces of evidence suggest that dinosaurs were cold blooded; however there is conflicting evidence to suggest otherwise.
Endothermy is the name for warm blooded animals which produce heat within the body. Modern endotherms include all birds and mammals. The heat is produced by the chemical reactions which digest food as well as when muscles contract during movement. Most endotherms are also homeotherms. This means that they can control their body temperature to with in four degrees of normal. Different ways this is accomplished is through sweating when they are too hot and shivering when they are too cold. While resting, a warm blooded animal has a body temperature that is constant and a little over the environmental temperature. It is not able to withstand sever variations from the environmental temperature without seeking shelter or utilizing thick skin or feathers as insulation. Some reasons why dinosaurs are believed to be endotherms include: Dinosaurs evolved alongside mammals, so they must have been endotherms in order to coexist with mammals successfully for the over 150 million years that they lived together. Some dinosaurs were massive; in order to survive they needed big, elaborate hearts to pump enough blood. Endotherms have large elaborate hearts and ectotherms do not. Dinosaurs were the ancestors of birds and since birds are endotherms, dinosaurs must have been the same. Dinosaurs walked upright with their legs below their bodies which is typical of endotherms. Ectotherms aren’t commonly found at higher elevations where most dinosaur fossils have been discovered. Dinosaur bones have more in common with bird and mammal bone structure than reptile bone. This similar bone structure shows that dinosaurs were endothermic. (www.ucmp.berkeley.edu) All of this evidence suggests that dinosaurs were endothermic, warm blooded creatures.
There are many pieces of evidence supporting both ideas of warm and cold blooded dinosaurs. The issue is a complex one with many different opinions and facts. The fact that a fossilized dinosaur heart was discovered is exciting and has shed light on the debate. "This gives us a nondestructive way to look inside specimens that are still embedded, as two-thirds of Willo is, in stone," John Fisher, director of the vet school's Biomedical Imaging Resource Facility says. "It's an amazing use of the technology." (http://www.memphisgeology.org/p_willo.html) Technology has helped uncover many mysteries of the dinosaurs and it is just a matter of time before we make the next groundbreaking discovery.
1. Dinosaur Blood 2 April 2004 <www.priweb.org>
2. Hot Blooded or Cold Blooded 3 April 2004 <www.ucmp.berkeley.edu>
3. Willo the Dinosaur with a Heart 2 April 2004 <http://www.memphisgeology.org/p_willo.html>
4. Fisher, Paul. Cardiovascular Evidence for an Intermediate or Higher Metabolic Rate in an Ornithischian Dinosaur 3 April 2004 http://www.sciencemag.org/cgi/content/full/288/5465/503
5. Dinosaur Heart Found 1 April 2004 http://news.bbc.co.uk/1/hi/sci/tech/720871/stm
6. Willo the Dinosaur with a Heart 1 April 2004 http://www.dinoheart.org/