Organ fossils bring new life to primitive fish evolution – New Scientist

Fossils of members of the ancient fish class Placodermi have been found in ancient rocks in Western Australia. They disturb the primitive fish family tree.

Search In the formation of the Australian Gogo, fossilized members of the extinct fish class Placodermi were discovered. The fossils are in very good condition: they are slightly affected by mold. The discovery means that the extant fish species and Placodermi have more in common than previously thought.

The fossils found indicate the presence of a liver with two lobes and a heart on the ventral side of the fish. Until now, researchers believed that these traits only evolved in the late jaws, a group descended from Placodermi, of which many subspecies now constitute the vertebrate group. But the found remains show that Placodermi also had such a liver with two lobes and a heart on the ventral side. Fossils provide more clarity about the evolution of jaw animals and the layout of their bodies.

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This concluded the paleontologist Kate Triangstickaffiliated with Curtin University in Australia. Fragments of petrified hearts, livers and abdomens were found in Placodermi. She and her colleagues compared the remains to other fish species, including sharks and sharks lamprey. From the similarities, I concluded that Placoderms have more in common with related fish species than previously thought.

“Much is still not clear about Placodermi,” says the paleontologist. Lars van den Hoek Ostend, who works at Leiden Naturalis. It is a collective name for different animals. Little is known about the evolutionary relationship with, for example, sharks and bony fish. So this result is an important step. The fossils found may explain what the Placodermi family tree looks like.

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Lidl Storage Box

Not surprisingly, the fossils were found in the western Australian Gogo Formation. “The Gogo Formation is a rock bundle in which special conditions prevail,” says Van den Hoek Ostende. It used to be a reef where fish could quickly sink to the depths after they died, in conditions of lack of oxygen. Bacterial activity there was minimal. As a result, a slight decay of the tissues occurred, so that the remains of the animals were well preserved. So you can see this configuration as a Lidl storage box, where you can pack food without oxygen. The soft parts of the fossils can also be preserved.

Van den Hoek Ostende has doubts about some of the statements made by Trinajstic and her team. Researchers say that Placodermi did not have lungs yet, because they had not found them. So you might think that the lungs actually developed later. But this evidence is a bit weak. After all, it can also mean that the lungs are less well preserved.

However, Van den Hoek Ostende is excited about the remains that have been found. Our knowledge depends mainly on skeletons. So now we can also look at the internal organs.

Winton Frazier

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