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Environment

First Fish

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Digging up a fossil does not bring instant enlightenment. Take, for example, a few scraps of bone that turned up in 1975 on the remote Arctic island of Spitsbergen. They were tiny chips covered with dense rows of bumps and dating back 500 million years. If they were scales, they were unlike anything seen before on a vertebrate. Some paleontologists even suggested that they were from the shell of a creature resembling a horseshoe crab. It wasn’t until this past year that compelling proof came: those bone chips belonged to the oldest fish yet found.

Paleontologists from the University of Birmingham in England took a close look at the microstructure of the fossils. They found that while the bone might look bizarre at low magnification, under a scanning electron microscope it had a familiar look. It had the typical combination of tubes and cavities that is unique to dentine--the hard tissue found in our teeth and in the scales of fish. The researchers concluded that the fossils came from the exoskeleton of Anatolepis, which was a small, lightly-armored jawless fish that rooted around in ocean muck.

Not only is Anatolepis the first fish, at least for now, but it’s also one of the earliest vertebrates--animals possessing, among other things, bone, a spinal cord, and a body made of segmented muscles and tissue. (In late-arriving vertebrate specimens like ourselves, the segments include our vertebrae.) In 1995 another mysterious group of animals called conodonts (which look like bug-eyed worms to the untrained eye) were also inducted into the ranks of early vertebrates. Since both conodonts and Anatolepis lived in the ocean, just off the continental shelf, and at the same time, they may finally resolve a long-running debate about whether early vertebrates evolved in freshwater streams or at sea: the winner seems to be the sea. Anatolepis, says Paul Smith, a member of the Birmingham team, is absolutely 100-percent-guaranteed marine.

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