When was the first vertebrate

Almost all living fish, amphibians, and reptiles are ectothermic. Their metabolic rate and level of activity depend mainly on the outside temperature. They can raise or lower their own temperature only slightly through behavior alone.

Both mammals and birds evolved endothermy. Endothermy means regulating bodytemperature from the inside through metabolic or other physical changes. On a cold day, for example, an endotherm may produce more heat by raising its metabolic rate. On a hot day, it may give off more heat by increasing blood flow to the surface of the body. Keeping body temperature stable allows cells to function at peak efficiency at all times.

The metabolic rate and activity level can also remain high regardless of the outside temperature. On the other hand, maintaining a stable body temperature requires more energy—and more food. What type of fish is a simple perch?

Vertebrate Evolution The earliest vertebrates were jawless fish, similar to living hagfish. Evolution of Fish Not too long after hagfish first appeared, fish similar to lampreys evolved a partial vertebral column. Evolution of Other Vertebrate Classes Amphibians, reptiles, mammals, and birds evolved after fish. The first amphibians evolved from a lobe-finned fish ancestor about million years ago.

They were the first vertebrates to live on land, but they had to return to water to reproduce. This meant they had to live near bodies of water. The first reptiles evolved from an amphibian ancestor at least million years ago.

They laid amniotic eggs and had internal fertilization. Subscribers, enter your e-mail address for full access to the Science News archives and digital editions. Not a subscriber? Become one now. To celebrate our centennial, we have made our entire archive available for free. But quality journalism comes at a price. Support the next century of science journalism. Skip to content. Science News Needs You Support nonprofit journalism.

By Carolyn Gramling October 25, at pm. There was a problem signing you up. Here, a selection of illustrated ancient fishes is shown. Nobumichi Tamura. The team that did the study gathered fossil data from around 2, specimens ranging from million to million years ago. Combining those records with environmental information, the paleontologists developed a model The conclusion helps explain the incomplete fossil record, the authors write in their report.