Animal World

Animal Characteristics and Activities

What was the first group of vertebrates?

The first vertebrates were fishes that appeared 500 million years ago. They were agnathans (from the Greek terms a, meaning “without,” and gnath, meaning “jaw”), small, jawless fishes up to about 8 inches (20 centimeters) long and also known as ostracoderms (“shell skin”) because their bodies were covered with bony plates, most notably a head shield protecting the brain.


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