Cambrian Explosion: a new study of early form fills a gap (Introduction)

by David Turell , Sunday, May 14, 2023, 18:54 (349 days ago) @ David Turell

Well preserved forms from China studied:

https://phys.org/news/2023-05-rare-fossils-gap-evolution-major.html

"Exceptionally well-preserved fossils from the Cambrian period have helped fill a gap in our understanding of the origin and evolution of major animal groups alive today.

"A new analysis of fossils belonging to an extinct invertebrate called Rotadiscus grandis have helped place this species in the animal tree of life, revealing how some characteristics of living species may have evolved independently rather than originating in a single common ancestor.

"Half a billion years ago, an unusual-looking animal crawled over the sea floor, using tentacles to pick up food particles along the way.

"Known as Rotadiscus grandis, this animal lived during the Cambrian period when a burst of evolutionary activity is thought to have given rise to many of the major animal groups we see today.

"The ancient remains of Rotadiscus were first discovered over 30 years ago, but the incomplete specimens made it challenging to determine their evolutionary significance.

"Now, a new study published in Current Biology describes Rotadiscus grandis in far more detail after rare, exceptionally preserved fossils were unearthed from the Chengjiang biota in Yunnan Province in China. The 518-million-year-old fossils have shone a new light on the evolution of early members of major animal groups.

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"Many animals from this period possessed unique anatomies that look very different to anything seen today. But the patchiness of the fossil record often makes deciphering what these species are or where they fit into the tree of life challenging for paleontologists.

"In the past, Rotadiscus and its closest fossil relatives have been placed in a number of different groups, including the sea cucumbers and jellyfish. But the new fossils of Rotadiscus from Chengjiang are helping to clear this up.

"The Chengjiang biota is famous for its exceptionally preserved Cambrian fossils. The likely reason is that these animals were buried by a mudflow very rapidly while they were still alive, entombing them and preventing decay by bacteria and scavenging by other animals.

"The new Rotadiscus fossils are no exception, as their extraordinary preservation has revealed structures in more detail than had previously been observed, such as traces of possible nerves in the tentacles and a new double spiral structure.

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"The new evolutionary tree including Rotadiscus and other fossils has helped the researchers reconstruct the evolution of major animal traits. One feature that was of particular significance was the presence of a tail extending posteriorly to the anus.

"Scientists originally believed that a post-anal tail was present in the common ancestor of all fish and acorn worms. However, as Rotadiscus lacks a post-anal tail it now seems that this trait may have evolved independently within these different groups.

"This process is known as convergent evolution, where the same feature evolves separately multiple times, often in response to similar environmental or ecological pressures.

"'Through our analysis, we can fill an evolutionary gap with Rotadiscus and its relatives," says Imran. "This is important because one of the goals for paleontologists is to try to understand the tree of life and how things are related to one another.'"

Comment: major work filing gaps in the evolutionary tree. But the study continues to demonstrate how stark the Cambrian gap really is. Unchanged since Darwin's time, all developments studying the source organisms of all our current species show the complexity of animals without precursors. Where did their brains come from??? is one question of very many. It all points to a designer at work, doesn't it?