Lamprey fossils can rewrite the history of vertebra evolution

Recently discovered fossils of various stages in the life cycle of the lamprey may dispel our notions of vertebra evolution.

New fossil finds indicate that speckled lamprey hats were more similar to modern adult lampreys, and were completely unlike their modern-day larval counterparts. .

The findings challenge a long-held notion that lamprey larvae are now trapped from the past, like the ancestors of all living vertebrates, people among them.

“We’ve basically been removing false eels from the spinal cord ancestry setting,” says Tetsuto Miyashita, a former associate of the University of Chicago and now a paleontologist at House- Canadian Nature Reserve. “So now we need another choice.”

“Lamps have an advanced life cycle.”

Lamps – unusual eel-like creatures – have long provided a glimpse into the evolution of the vertebra, says Miyashita, the first author of the new paper on its findings. Nature.

“Lamps have an advanced life cycle. Once born, the larvae bury themselves in the river bed and spawn before finally metamorphosing into blood-sucking adults. They are so different from adults that scientists originally thought they were a completely different group of fish.

“Modern day lamprey larvae have been used as a model of the ancestral condition that led to the spinal cord. They looked primitive enough, compared to vertebrate invertebrates, and their features best matched the vertebra ancestry. But we had no evidence that such a fundamental shape goes all the way back to the beginning of vertebral evolution. ”

Recent fossils found in Illinois, South Africa and Montana change the story. Connecting the dots between dozens of samples, the research team realized that different stages of the life cycle of eels were preserved, allowing paleontologists to monitor their growth from birth to adulthood.

On some of the smaller specimens, about the size of a fingerprint, the preservation of a soft print even shows the remains of a yellow sac, indicating that a fossil record had briefly caught these speckled eels. after crying.

Crucially, these fossil juveniles are in stark contrast to their modern counterparts (known as “ammocoetes”), and instead look more like adult adult eels of today. today, with big eyes and a toothy mouth. Interestingly, this phenotype is seen at the larval stage in several different species of lamprey.

“Surprisingly, we have enough samples to reproduce a pathway from hatching to adulthood in several independent rows of early lampreys and they all show the same pattern: the larval shape was similar to small adult, ”says Michael Coates, professor of organic biology and anatomy. ”

“Lampreys are nothing like the swimming time capsules we once thought they were. ”

The researchers say these findings challenge the 150-year-old evolutionary statement that modern-day lamprey larvae give us insight into deep-ancestral spinal cord conditions. . By showing that ancient lampreys have never gone through the same blind, seed-feeding stage seen in modern species, the researchers have emptied this popular ancestral model.

Having looked back at the fossil record, the team now believes that extinct armed fish called ostracoderms may represent better candidates for the root of the vertebrate family tree, but newer modern lamprey larvae.

The team believes that the evolution of seed-feeding larvae may have allowed eels to build rivers and lochs. Fossils reported in the new study all came from marine sediments, but modern lampreys usually live in freshwater.

This is the kind of discovery that textbooks can rewrite, the researchers say.

“Lampreys are not the swimming pool capsules we once thought they were,” Coates says. “They remain important and essential to understanding the deep history of spinal cord diversity, but we must also recognize that they have also evolved and specialized in themselves.”

Additional coauthors are from the Albany Museum in South Africa and the University of Kansas. The work was supported by the National Science Foundation.

Source: University of Chicago