Artist’s reconstruction showing the life stages of the fossil lamprey Priscomyzon riniensis. It lived around 360 million years ago in a coastal lagoon. Clockwise from right: A tiny, yolk-sac carrying hatchling with its large eyes; a juvenile; and an adult showing its toothed sucker.
© Kristen Tietjen
Here is a little news item of a sort that normally has Creationists' pulses racing while loudly declaring victory and the death of Darwin's hated Theory of Evolution. It is the discovery by a bunch of researchers with the Canadian Museum of Nature, the University of Chicago and the Albany Museum in South Africa that what we thought we knew of the early evolution of the vertebrates was wrong and, to coin a cliché, the textbooks now need to be rewritten.
The reality is though, that this is merely science doing its job and checking the facts and revising the information that we thought we had, now we know better.
What we thought was that the larvae of early lampreys were pretty much like the larvae of modern lampreys and thus represented a very primitive vertebrate, close to the basal vertebrates that all vertebrates subsequently evolved from.
From this recent research however, it appears that the larvae of early lampreys were not simple, blind filter-feeders with no mouth-parts as we thought and were really much more like their adult forms, complete with large eyes and a fully developed toothed suctorial disc for a mouth.
The news release from the Canadian Museum of Nature explains:
Fossil of the hatchling of Priscomyzon, from the Late Devonian around 360 million years ago. The hatchling is already equipped with large eyes and toothed sucker, which in modern lampreys only develop in adults. (The Canadian 25-cent coin offers a size comparison for the tiny fossil)
Credit: Tetsuto Miyashita © Canadian Museum of Nature
Incidentally, as an added disappointment to Creationists, did anyone spot the comment about modern lamprey larvae evolving into their modern, simple form by loss of complexity?Long-accepted theory of vertebrate origin upended by fossilized lamprey larvae
Ottawa, March 10, 2021 – A new study of fossilized lampreys dating from more than 300 million years ago is challenging a long-held theory about the evolutionary origin of vertebrates (all animals with a backbone). The findings are published March 10 in the science journal Nature.
Lampreys are ancient, jawless, eel-like fishes that arose around half a billion years ago and they have long provided insights into vertebrate evolution. Now, scientists with the Canadian Museum of Nature, the University of Chicago and the Albany Museum in South Africa are reporting their analysis of dozens of tiny fossils that track the life stages and growth of ancient lampreys, from hatchlings to juveniles to adults.
We’ve basically removed lampreys from the position of the ancestral condition of vertebrates, so now we need an alternative.Their results counter the established view that the blind, filter-feeding larvae of modern lampreys (called ammocoetes) are a holdover from the ancestors of all living vertebrates. The new fossil discoveries show that ancient lamprey hatchlings were completely unlike their modern larvae counterparts.
Once hatched, the larvae of modern lampreys bury themselves in a riverbed and filter feed before eventually metamorphosing into blood-sucking adults. The larvae are so different from adults that scientists originally thought they were different species. Even after finding out they are just an early phase in the lamprey life cycle, scientists saw the image of our distant ancestors in these seemingly primitive larvae.
Lampreys solved this problem [of rivers and lakes being tough environments in which to migrate because of the limited and unpredictable supply of prey] by burrowing in sand and slurping up whatever food particles were available until they could mature enough to start looking for prey with blood, but you don’t have to be too complicated for this kind of lifestyle. So even though lampreys invented this filter feeding larval phase anew, the larvae themselves looked simple and primordial. Until now we were misinterpreting this simplicity for primitiveness.
Tetsuto Miyashita, Ph.D, Lead author
Palaeontologist with the Canadian Museum of Nature.
“We’ve basically removed lampreys from the position of the ancestral condition of vertebrates,” explains lead author Tetsuto Miyashita, Ph.D, a palaeontologist with the Canadian Museum of Nature. “So now we need an alternative.”
Miyashita explains that lampreys have a curious life cycle. “Once hatched, the larvae of modern lampreys bury themselves in a riverbed and filter feed before eventually metamorphosing into blood-sucking adults. The larvae are so different from adults that scientists originally thought they were different species. Even after finding out they are just an early phase in the lamprey life cycle, scientists saw the image of our distant ancestors in these seemingly primitive larvae.”
The newly discovered lamprey fossils are now changing this story. The fossils, belonging to four extinct species, were discovered in South Africa and the United States (Illinois and Montana) and range in age from 310 to 360 million years old. The researchers found that the smallest individuals, barely 15mm in length (fingernail sized), still carried a yolk sac, signalling that these had only just hatched before dying. Further examination revealed that these youngsters already had large eyes and were armed with a toothed sucker, characteristics that in modern lamprey species only develop in the adults.
“Remarkably, we’ve got enough specimens to reconstruct a trajectory from hatchling to adult in several independent lineages of early lampreys,” said Michael Coates, Ph.D, a biology professor at UChicago and co-author of the study along with Rob Gess, Ph.D at the Albany Museum and Kristen Tietjin at the University of Kansas. “They each show the same pattern: the larval form was like a miniature adult.”
Remarkably, we’ve got enough specimens to reconstruct a trajectory from hatchling to adult in several independent lineages of early lampreys. They each show the same pattern: the larval form was like a miniature adult.The researchers say that these results run counter to the 150-year-old evolutionary narrative that modern lamprey larvae, with their curious life cycle, offer a glimpse of deep ancestral vertebrate conditions. By demonstrating that ancient lampreys never went through the same blind, filter-feeding stage seen in modern species, the researchers have falsified the conventional ancestral model shared in textbooks.
They remain important and essential for understanding the deep history of vertebrate diversity, but we also need to recognize that they, too, have evolved and specialized in their own right.
Professor Michael Coates, Ph.D, Co-author
Professor of biology
University of Chicago
After their examination of the fossil record, the researchers now believe that extinct armored fishes known as ostracoderms might instead represent better candidates for the root of the vertebrate family tree, whereas modern lamprey larvae are a more recent evolutionary innovation.
If so, then why do modern lamprey larvae appear so primordial? The team suggests that the evolution of filter-feeding larvae may have been an innovation that allowed lampreys to populate rivers and lakes. Fossil lampreys reported in the new study all came from marine sediments, but modern lampreys, with their filter-feeding, blind larvae, mostly live in freshwater.
For ancient blood-sucking lampreys, rivers and lakes would be tough environments in which to migrate because of the limited and unpredictable supply of prey. “Lampreys solved this problem by burrowing in sand and slurping up whatever food particles were available until they could mature enough to start looking for prey with blood,” said Miyashita. “But you don’t have to be too complicated for this kind of lifestyle. So even though lampreys invented this filter feeding larval phase anew, the larvae themselves looked simple and primordial. Until now we were misinterpreting this simplicity for primitiveness.”
The researchers say that this is the sort of discovery that can rewrite textbooks. “Lampreys are not quite the swimming time capsules that we once thought they were,” said Coates. “They remain important and essential for understanding the deep history of vertebrate diversity, but we also need to recognize that they, too, have evolved and specialized in their own right.”
There is, of course, no suggestion by the authors that this finding represents a serious problem for the TOE or any hint that the TOE is a 'theory in crisis', merely that the known facts are now not consistent with what was thought about the evolution of early vertebrates, in particular which primitive organisms were the real stem vertebrates. That focus now shifts onto the ostracoderms or armoured fish.
Evolution is still the fundamental foundation of biology and the only theory capable of explaining these new findings and adjusting to fit them.
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