Bloodsucking Lamprey Found to Be "Living Fossil"
for National Geographic News
|October 25, 2006|
Add the lamprey to the list of "living fossils."
A 1.7-inch (4.2-centimeter) fossilized specimen found in an ancient South African lagoon shows that the bloodsucking, eel-like fish hasn't changed much in 360 million years, according to a new study to be published tomorrow in the journal Nature.
(See another newfound "living fossil": the first new mammal discovered in Europe in a hundred years.)
The ancient lamprey attached its toothy, suckerlike mouth to, for example, prehistoric sharks almost exactly the same way that modern lampreys latch onto other fish today, the study says.
As the prehistoric lamprey's hosts went extinct or evolved into new species, "the lamprey simply evolved into a lamprey,'' said study co-author Michael Coates, a biologist at the University of Chicago in Illinois.
Like modern lampreys, this ancient lamprey had a backbone made not of bone but of cartilage—the generally translucent, somewhat flexible substance that gives human noses and ears their shapes and that makes up shark skeletons.
Perhaps most important, the new discovery is "the first lamprey fossil to give us a good view of the mouth,'' Coates said.
The fossilized lamprey had a jawless mouth ringed with horny teeth, like modern lampreys. This jawless mouth sets the lamprey and its cousin the hagfish apart from all other modern vertebrates—animals with backbones.
It is believed that jawless marine animals were the first vertebrates and that they emerged sometime after 540 million years ago.
The Great Divide
When the fossilized lamprey lived, there were probably many types of jawless vertebrates. Except for the lamprey and hagfish, all of them seem to have died out.
"This fossil shows that the lampreys are the closest living representatives of backboned animals of that era,'' Coates said.
Paleontologists believe that, over millions of years, lamprey-like creatures evolved into jawed, bony fish.
If these proto-lampreys were the first vertebrates, they may be the common ancestors to all animals with backbones, including humans.
The evolutionary split between jawless and jawed fish probably happened close to 500 million years ago, according to Michael Miyamoto and colleagues at the University of Florida in Gainesville.
During a genetic study reported in a February issue of the journal Proceedings of the National Academy of Sciences, Miyamoto discovered that the cartilaginous lamprey backbone and the human backbone are built from the same essential protein, collagen.
This seems to confirm that lampreys and humans share an ancient common ancestor that produced collagen, he says.
Not Quite Twins
Though the ancient lamprey is remarkably similar to modern varieties, there are differences.
The fossilized fish is just 1.7 inches (4.2 centimeters) long. Modern adult lampreys measure anywhere from about 6 to 40 inches (15 to 100 centimeters) long.
The ancient lamprey had a much larger mouth, proportionately speaking, than modern lampreys do. In addition, the prehistoric fish had one long dorsal fin, whereas many lampreys today have more. And the fossil creature had 14 teeth, compared with the modern lamprey's 19.
Though the newfound fossil is significant, the discovery of almost any lamprey fossil is cause for celebration.
Unlike with bony fish, only a handful of lamprey fossils have ever been found, because cartilage usually decays too fast to become fossilized.
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