The resemblance soounded so nice and neat a Darwinian belief that few can have wanted, in these times, to subject it to scrutiny. But some people did:
A study of fossilized lampreys dating from more than 300 million years ago is challenging a long-held theory about the evolutionary origin of vertebrates. These ancient, jawless, eel-like fishes arose around half a billion years ago and they have long provided insights into vertebrate evolution. The analysis of the fossils counters the established view that the blind, filter-feeding larvae of modern lampreys (ammocoetes) are a holdover from the ancestors of living vertebrates.Canadian Museum of Nature, “Long-accepted theory of vertebrate origin upended by fossilized lamprey larvae” at ScienceDaily
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.
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.
“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.Canadian Museum of Nature, “Long-accepted theory of vertebrate origin upended by fossilized lamprey larvae” at ScienceDaily
The researchers think that filter feeding in the young was a later adaptation. They are not especially kind to received wisdom:
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.Canadian Museum of Nature, “Long-accepted theory of vertebrate origin upended by fossilized lamprey larvae” at ScienceDaily
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.”Canadian Museum of Nature, “Long-accepted theory of vertebrate origin upended by fossilized lamprey larvae” at ScienceDaily
It’s almost like they don’t mind rewriting the textbooks. It’s as if they don’t “trust science” or something.
The paper is closed access.