Science & Technology

The hatching of these fossilized lampreys disproves the ancient theory of evolution.

Illustration of a hatched lamprey found in South Africa. (Kristen Tietjen /)

You are not a descendant of a water vampire. For more than 100 years, evolutionary biologists have found that lamprey, a jawless, eel-shaped, blood-sucking fish, is the closest living to the first vertebrate, although it is unlikely that it had ever thought of it. I suspected that it was a model.

Despite how it sounds, it’s not an unreasonable suspicion. Lamprey is one of the few animals on the border between vertebrate and invertebrate ancestors. Adult lampreys have a spinal column and swim in the water in search of fish. The fish gets caught in the tooth-filled mouth and bleeds. But “the early stages of their lives are quite different and ridiculous,” says Tetsuto Miyashita, a vertebrate paleo-vertebrate zoologist at the Canadian Museum of Nature.

The larval lamprey lives like a sea anemone, burying it in the riverbed for the first two to seven years of its life and filtering food from the water with a toothless, muscular throat. Lamprey has long been treated as the earliest model of vertebrates because it resembles invertebrates so much. To be exact, it is a doppelganger, not our ancestor.

“This is a primitive animal that has changed from this primitive state,” explains Miyashita. “It looked like something similar to what must have happened in the early stages of evolution. It’s a very useful story.”

But the study A new fossil of a Paleozoic lamprey larva was published in the journal on Wednesday. Nature, I turned the story over. “It was very clear to me that it overturned the theory of evolution 150 years ago, just as the icicles of that morning hung on the roof,” says Miyashita, the lead author of the study.

Biologists had previously questioned lamprey’s ancestral theory, but the problem was in the sparse fossil record of lamprey. To disprove the theory, scientists will need to show that lampreys began to be completely fish-like and then evolved into the shape of their sedentary larvae.

Therefore, this new study depends on a series of notable fossils. Hatched lampreys include those that are still young enough to carry egg yolks. “The moment I saw it, it was clear that it had just hatched with a yolk sac,” says Miyashita. But it wasn’t like the larvae that feed the bottom of modern lampreys. “It already had a sucker with big eyes and a toothed mouth. It was like a miniature adult.”

A fossil of the hatched paleozo lamprey in Illinois.

A fossil of the hatched paleozo lamprey in Illinois. (Tetsuto Miyashita /)

Miyashita, who likes baseball analogies, says that finding a fossilized, newly hatched baby turtle “goes to the baseball stadium and catches the ball hit by a player who has never hit a home run in 25 years.” It is said that it was a good one. The smallest fossil fits in the little fingernail and has no bones or teeth. A soft tissue engraved on the bottom of a muddy lagoon.

Researchers have collected more fossils from the site, showing mature species of life-sized lampreys and specimens of other juveniles of the same period around the world. “This is a pattern that is retained across time and space,” says Miyashita, not just evidence of one strange baby lamprey.

In short, he says, the larval stage is not an inheritance from the past, but a “totally new evolutionary innovation.”

Margaret Docker, a lamprey biology and genetics expert at the University of Manitoba, calls the findings “very exciting.” She agrees that fossils “exclude modern lampreys as models of the earliest vertebrates.”

Docker has previously proposed another model of lamprey evolution, including ancestors with several traits, both larvae and adults. Now it’s too early to know if these fossils are for or against the theory, she says. Still, she agrees with the overall takeaway. “We run into problems when we treat modern lampreys as” living fossils. “

Larva of the modern Pacific lamprey.

Larva of the modern Pacific lamprey. (Gregory Kowartuk /)

However, the findings raise two new questions. Why did lampreys evolve into such misleading creatures, and what did early vertebrates actually look like?

The first answer seems to be related to the habitat of modern lampreys. From brackish lakes to lagoons to offshore deltas, all ancient fish-like lamprey larvae were found in saltwater environments, Miyashita says. And they are some of the most biologically productive ecosystems on the planet. Consider the large shrimp industry in the Mississippi or Mekong deltas.

“It’s in stark contrast to modern lampreys,” says Miyashita. Most of them live in freshwater rivers and lakes. “And all species begin their life cycle in streams.”

These riverbeds are barren compared to coastal wetlands. “The larval shape allows us to chew the cherries, a resource of life, twice,” said Michael Coates, the lead author of the treatise and a vertebrate paleovertebrate zoologist at the University of Chicago. .. “That means you have a big gap between boys and adults. In a sense, they live in different ecosystems.” Even if food is scarce at one life stage, the whole population Is not wiped out.

It is not clear why lampreys have left the rich coastal waters in the first place. Both Miyashita and Coates point out that lampreys survived four of the Earth’s five major extinction events, speculating that their hybrid lifecycle might have been part of their resilience. ..

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Coates also states that there are many “relics” species of fish that have been retained only in rivers and streams, primarily in North America. Bowfin, alligator gar, and sturgeon are all the last living examples of a once large family of fish that have been pushed out of the open ocean and evacuated inland. Lamprey may be part of that pattern.

For early vertebrates, Mayashita and his co-authors claim that another group of fish featuring skin bone armor is closer to Mark. It seems to have produced other boneless vertebrates, such as lampreys, which have no jaws. “The bones seem to be running deep,” says Coates. In other words, lampreys, sharks, and other animals are not primitive due to their lack of bones, but at some point they gave up.

If the “primitive” characteristics of lamprey are actually special adaptations, it also has important implications for other studies that treat lamprey as a baseline. Of particular interest is the fact that lampreys can regenerate the spinal cord. This is a life-changing property if humans come from the same root.

“From the genome to biomedical engineering to evolutionary biology, the idea is that lampreys can be seen as a useful model for primitive vertebrates,” says Mayashita. “Now we have to stop and think about it.”

The hatching of these fossilized lampreys disproves the ancient theory of evolution. The hatching of these fossilized lampreys disproves the ancient theory of evolution.

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