New findings by paleontologists contradict the conventional wisdom that the blind filtering larvae of modern lampreys – ammocoetes – are the prototype for the early developmental stage of all vertebrates, scientists told TOPNEWS. It turned out that fry of ancient lampreys are completely different from their modern counterparts, but rather resemble adults in miniature. Now scientists propose ostracoderms as the ancestors of vertebrate armored jawless fish. The research results are published in the journal Nature.
Lampreys are eel-like jawless fish that appeared on Earth half a billion years ago. Modern lampreys have an unusual life cycle. They live in freshwaters. Adults are external parasites that stick to large fish and feed on their blood. Lamprey larvae – sandworms, or ammocoetes – after emerging from eggs burrow into the silt and pass a water stream through themselves, filtering detritus and microscopic organisms from it.
The larvae are so different from the adults that scientists initially thought they belonged to a separate species. And when it turned out that this was only a stage of development, they saw in the primitive larvae of lampreys the prototype of the distant ancestors of all vertebrates.
Recently, paleontologists have found lamprey fossils between 310 and 360 million years old in Carboniferous sediments in South Africa and the United States. The value of these finds lies in the fact that among them all stages of development of ancient animals are represented – from newly hatched fry, barely reaching 15 millimeters in length, and not yet deprived of their yolk sac, to adults. It turned out that the ancient lampreys, which, unlike their modern counterparts, lived in the sea, and not in freshwater, did not go through the stage of ammocoetes.
“It is noteworthy that we have enough samples to reconstruct the trajectory from hatching to adult in several independent lines of early lampreys,” said one of the study authors Michael Coates, professor of the Department of Biology and Anatomy of Organisms, in a press release from the University of Chicago. “Each of them shows the same picture: the larva looks like a miniature adult.”
Newly hatched fry already had large eyes and “toothy” suckers, which develop in modern lampreys only in adulthood.
“Modern lamprey larvae were used as a model of the inherited condition that led to the emergence of the vertebrate lineage,” says lead author Tetsuto Miyashita of the Canadian Museum of Nature. a description of rudimentary forms dating back to the early evolution of vertebrates. But now we have practically excluded lampreys from the ancestors of vertebrates. Now we need an alternative. ”
Perhaps, the authors believe, such an alternative can be the armored jawless fish of the ostracoderm, which can now be considered as the root element of the family tree of vertebrates.
“Lampreys are not at all the time capsule we once thought,” Coates notes.
The stage of filtering larvae in modern lampreys arose in the process of evolution, scientists say. Perhaps this innovation allowed lampreys to colonize freshwater reservoirs, where there was much less fish than in the seas.
“Lampreys solved this problem in this way. Their larvae buried themselves in the ground and swallowed all available food particles until they were ripe enough to start looking for their own prey,” explains Miyashita.