Reptilia are ectothermic (coldblooded) and birds are endothermic (warmblooded). Temperature extremes harm animals irrespective of whether they are endothermic or ectothermic. Many ectothermic vertebrates have no sex chromosomes. Scientists disagree as to whether non-avian dinosaurs were endothermic, ectothermic, or some combination of both. Like other reptiles, geckos are ectothermic, producing very little metabolic heat. Like other amphibians, the Chinese giant salamander is ectothermic. Almost all fish are cold-blooded (ectothermic). Mammalian blood flow index is about 10 times greater than in ectothermic reptiles. "Tyrannosaurus", like most dinosaurs, was long thought to have an ectothermic ("cold-blooded") reptilian metabolism. This process is useful to ectothermic (cold-blooded) animals in the regulation of their body temperature. Being ectothermic ("cold-blooded"), the surrounding temperature plays a large role in snake digestion. Brown bullheads are ectothermic, heterothermic, and bilaterally symmetrical. After non-avian dinosaurs were discovered, paleontologists first posited that they were ectothermic. The study contradicted findings published in 2010 indicating mosasaurs were ectothermic. The developmental period for "D. melanogaster" varies with temperature, as with many ectothermic species.