Derpy from the side and hell from below, the lamprey is the bane of the Great Lakes fishery. A jawless, blood-sucking fish, the lamprey is often considered an ancestral early vertebrate fish due to its seminal morphology and its larval life stage. Now, a team of researchers has written a new study on fossilized Devonian lamprey larvae, which they say show that lamprey evolution took place differently than previously thought. This would mean changing our story about the origin of vertebrates.
The researchers’ paper was published Wednesday in the journal Nature. Their argument depends on the lamprey life cycle. Modern lamprey larvae called ammocoetes are blind filter feeders, later turning into their noodle-like, predatory adult selves. Biologists and paleontologists have viewed that ammocut larval stage as a relic of early vertebrate evolution, and a sign that the lamprey can be trusted as a living fossil that helps explain where all hind-legged animals came from. But the recent team describes fossils of baby pricks that are not ammocoetes – these fossils look like smaller versions of adult pricks – suggesting that that larval stage was a later evolutionary adaptation, one unique to pricks.
“Now it looks like the jabs are the weird ones,” Tetsuto Miyashita, a paleontologist at the Canadian Museum of Nature and lead author of the paper, said in a video interview.[The lamprey] looks primitive, more primitive than these extinct jawless fish. But it was the other way around. “
Miyashita’s team describes four different types of ancient lamprey from Africa and North America, ranging from 360 to 310 million years old. At the time, the places in Montana, Illinois, and South Africa (where the eel-like pricks were dug up) were shallow seas; a different habitat than the fresh waters where most of the punctures nowadays meander.
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The non-ammocoet fossil lamprey weren’t a smaller group of adult lampreys, the team says, as some of the fossilized fish even have yolk sacs still attached to their bodies. If that were only in one place, “we would have thought we were looking at this really weird, specialized, extinct line of the lamprey doing its own thing and maybe losing the filter-feeding larval phase,” Miyashita said. “But kind after kind after kind, across four different lineages of fossil prickles, they show the same thing.”
The authors argue that the ammocoetic larval stage was an adaptation that the lamprey evolved to move into the freshwater environments in which they now thrive. In the 20th century, numerous attempts were made to use the invasive lamprey population in the Great Lakes. The lampreys were first observed in Lake Ontario in 1835 and spread to the other great lakes in the mid-20th century. Now the established population is wreaking havoc on the lakes’ trout, whitefish, ciscoes and other fish species, clamping them with their suction cups and eventually killing them. In the 1960s, annual Great Lakes catches were 2% the previous average; a dramatic dive attributed to the jabs.
“These species, like the lamprey, which we think of as ‘ancient fish’, have been evolving just as long as we are and are not frozen in time,” said Jera.Miah Smith, a biologist at the University of Kentucky who was not affiliated with the recent paper, in an email. “More broadly, the study clearly shows the importance of considering alternatives to generally accepted evolutionary scenarios, and how new datasets continue to shape our understanding of the deep evolutionary history of vertebrate lineage.”
As an alternative candidate for a vertebrate ancestor, the researchers propose the armored Devonian fish, called ostracoderms, which look a lot like tadpoles going to war.
“Lampreys aren’t quite the swim time capsules we once thought they were,” said study co-author Michael Coates, a biologist at the University of Chicago, in a Canadian Museum of Nature. press release“They remain important and essential for understanding the deep history of vertebrate diversity, but we must also recognize that they, too, have evolved and specialized on their own.”
This story has been updated with comments from Jeramiah Smith.