PROBLEMS WITH DINOSAURS EVOLVING INTO BIRDS

 

Warm-blooded vs. cold-blooded

Seemingly forgotten in all the claims that birds are essentially dinosaurs (or at least that they evolved from dinosaurs) is the fact that dinosaurs are reptiles. There are many differences between birds and reptiles, including the fact that (with precious few exceptions) living reptiles are cold-blooded creatures, while birds and mammals are warm-blooded. Indeed, even compared to most mammals, birds have exceptionally high body temperatures resulting from a high metabolic rate.

 

IN AN EFFORT TO MAKE THE EVOLUTION OF DINOSAURS INTO BIRDS SEEM MORE PLAUSIBLE, SOME EVOLUTIONISTS HAVE ARGUED THAT DINOSAURS WERE ALSO ENDOTHERMIC.

 

The difference between cold- and warm-blooded animals isn’t simply in the relative temperature of the blood but rather in their ability to maintain a constant body core temperature. Thus, warm-blooded animals such as birds and mammals have internal physiological mechanisms to maintain an essentially constant body temperature; they are more properly called “endothermic.” In contrast, reptiles have a varying body temperature influenced by their surrounding environment and are called “ectothermic.” An ectothermic animal can adjust its body temperature behaviorally (e.g., moving between shade and sun), even achieving higher body temperature than a so-called warm-blooded animal, but this is done by outside factors.

 

In an effort to make the evolution of dinosaurs into birds seem more plausible, some evolutionists have argued that dinosaurs were also endothermic, but there is no clear evidence for this.

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One of the lines of evidence for endothermic dinosaurs is based on the microscopic structure of dinosaur bones. Fossil dinosaur bones have been found containing special microscopic structures called osteons (or Haversian systems). Osteons are complex concentric layers of bone surrounding blood vessels in areas where the bone is dense. This arrangement is assumed by some to be unique to endothermic animals and thus evidence that dinosaurs are endothermic, but such is not the case. Larger vertebrates (whether reptiles, birds, or mammals) may also have this type of bone. Even tuna fish have osteonal bone in their vertebral arches.

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Another argument for endothermy in dinosaurs is based on the eggs and assumed brood behavior of dinosaurs, but this speculation too has been challenged. There is in fact no theropod brooding behavior not known to occur in crocodiles and other cold-blooded living reptiles.

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Alan Feduccia, an expert on birds and their evolution, has concluded that “there has never been, nor is there now, any evidence that dinosaurs were endothermic.” Feduccia says that despite the lack of evidence “many authors have tried to make specimens conform to the hot-blooded theropod dogma.” - Dr. David Menton (Answers in Genesis)