Examples Of Poikilothermic Ectotherms

Just like their relatives, our modern day reptiles, dinosaurs were long thought to be poikilothermic ectotherms. Like reptiles, many believe that dinosaurs were slow, sluggish and unable to regulate and maintain a homeostatic body temperature internally, by themselves, as endotherms are able to. Endotherms regulate body temperature internally with their metabolism. When compared to ectotherms, endotherm cells possess a larger number of Mitochondria within each cell. Mitochondria are like the power plants of our bodies. These mitochondria perform the process of cellular respiration. Cellular respiration is an intracellular process that converts energy found in bonds of nutrients like glucose and lipids into ATP. ATP is the main energy currency

Much of the energy used to create ATP during cellular respiration is lost as heat. This produced heat is the mechanism largely used by endotherms to regulate their internal body temperatures. To maintain such a high metabolic rate, endotherms would have to seek out a constant supply of nutrients to fuel cellular respiration, and internal heat production, thus, they would have a much more active lifestyle than poikilothermic ectotherms. Since dinosaurs were thought to be poikilothermic ectotherms they do not internally regulate their body temperature with heat produced by a high metabolism. They would not have required such a steady supply of nutrients to fuel cellular respiration the way endotherms do. Thus dinosaurs would have a much lower activity level and be more slow and sluggish, more like the reptiles of modern day. One of my favorite childhood memories is going to see Jurassic Park in the movies. This information paints a very different picture than the one I saw in the movie, where the dinosaurs were highly active, trying to eat anyone in their

A plethora of fossils have been found in the Cretaceous Arctic Circle. If dinosaurs were found in the Arctic Circle, where temps were sure to be cold, they would have needed to have possessed the ability to self-regulate their body temperatures. This was thought to further the argument of endothermy, but this also may be false indication. According to Benson “there was no evidence of glaciation in the Mesozoic and climates at these high latitudes need not have been cold” (Benson 1979, 984).
Bone histology may be another possible indicator of endothermy. Dinosaurs possessed highly extensive Haversian systems. Haversian systems are largely responsible for internal remodeling as well as bone regeneration. These were thought to be an indicator of endothermy because all living endotherms also possess extensive Haversian systems, by comparison they are less developed in extant ectotherms such as reptiles, but some now believe this is thought to be linked to large size rather than