Billie Burton, age 14, of Milwaukee, Wisconsin, for his question:

What were the Devonian armored fishes like?

They came in many shapes and sizes and most of them resembled robots designed to scare small children. But when these armor plated fishes lived, they were the most advanced animals on our planet. They dominated life in the ancient seas for 100 million years, sharing the latter part of their reign with large and smallish sharks. The armored fishes have been extinct for about 300 million years and they may or may not have been the direct ancestors of our modern bony fishes.

Suppose we could telescope the history of the earth into a single year. The Devonian Period would whisk by during the second week of November. It is known as the Age of Fishes and actually lasted about 60 million years. The climate was mild, the oceans flooded much of the land with shallow water and everything favored the acceleration of life in the sea. When this period opened, the sea was the cradle of all living things. When it closed, early plants and animals were well established on the dry land.

The Devonian inherited corals and a large variety of invertebrate sea dwellers from previous ages. It also inherited the first vertebrate, complete with a bony spine and internal skeleton. However, this fishy fellow also inherited a protective outer coat of crusty armor. His head and shoulders were fitted with bony plates and the rest of his body was covered with tough little shells. He was Ostracoderm, the shell skinned fish. Both his fan shaped tail and the pair of primative fins under his chin were covered with little shells. He had no jaws and his round mouth was suitable for sucking up food from the muddy sea floor.

Ostracoderm was somewhat streamlined and often three feet long. Some of his cousins were shorter or thicker or had more bony plates. Some of these species may or may not have given rise to the true armored fishes    the placoderms. Early in the period, the ancient seas were populated with various species of shell skinned and true armored fishes. Both types were similar, though the placoderms had more bony armor and tended to come in more fantastic shapes. They had one other remarkable feature that set them apart.

None of those clumsy early fishes were very mobile. But the placoderm had a special joint that slightly raised the top of his skull. This enabled him to grab his food and gradually gave rise to jaw bones. Toward the end of the Devonian Period, some of the armored fishes had jaws with teeth for seizing, tearing or crushing. No doubt they were more successful than the jawless, shell skinned fishes, though they survived only a few million years longer.

Some armored fishes were mackerel sized and others were three feet long. One species had humped shoulders and bony plates over the front half of his body. Another had huge, shell covered fins like rounded wings. One fantastic species had a pair of erect fins, like spikey horns behind his bony, bullet shaped head, plus a dorsal fin and a variety of shell covered fins on his underside.