New Ediacaran fossils; a form living in the Cambrian era (Introduction)

by David Turell , Friday, August 10, 2018, 20:16 (2297 days ago) @ David Turell

The Ediacarans are simple animal forms which lived well into the Cambrian era, but they do explain the gap in body complexity:

https://phys.org/news/2018-08-evolution-rethink-scientists-closer-earth.html

"Fossils of Stromatoveris psygmoglena are found in only one place in the world: Chengjiang county, China. This region is known for exceptionally well-preserved Cambrian fossils from 518m years ago.

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"While the fossil record most often preserves only hard shells or bones, some special sites like Chengjiang preserve the remains of soft-bodied animals, such as Stromatoveris psygmoglena. Originally described in 2006 from eight known specimens, we examined over 200 new fossils of the organism that have since been discovered by researchers from Northwest University, China, and dated to the Cambrian period.

"The way in which fossils of the Ediacaran Period were preserved has been another of their mysteries. These fossils often show signs of bending, twisting and tearing, suggesting that they preserve soft-bodied organisms without hard parts. However, there is rarely anything left of the soft tissues themselves.

"Instead, they left moulds in the surrounding sediment, a little like a footprint on the beach. In contrast, the newly examined Cambrian fossils of Stromatoveris psygmoglena retain carbon-based tissue, allowing us to see the detailed and internal anatomy of the body itself.

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"The analysis showed that Stromatoveris psygmoglena and seven key members of the Ediacaran biota share very similar anatomies, including multiple, branched fronds which radiate outwards like seaweed, uniting them all in a new group of early animals called Petalonamae. The name means "Nama Petals" and was chosen to honour biologist Hans Pflug and his work on the Ediacaran biota in Namibia, a reference to the petal-like fronds which, Pflug noted, distinguish these unusual animals.

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"Because members of the Ediacaran biota can now be classed as animals, we can date the origin of the animal kingdom to at least the time when these fossils appeared. The oldest members of these groups are known as "rangeomorphs" and appear in the fossil record approximately 571m years ago, in the late Ediacaran Period.

"This means that animal species were diversifying well before the Cambrian explosion. It may also mean that the search for animal origins should now focus on the time before this, in the early Ediacaran and even more ancient geological periods. Based on this, animals may have originated much earlier than the traditional reading of the fossil record had suggested.

"This study also has key implications for the ecology and eventual extinction of the petalonamids. Many Ediacaran species have not been found in later rocks leading some researchers to think that they were a "failed experiment" in evolution, disappearing by the beginning of the Cambrian. Indeed, this was my own view until I saw the remarkable new fossils of Stromatoveris psygmoglena.

"The inclusion of this Cambrian animal among the petalonamids changes the picture of the Ediacaran biota. Stromatoveris psygmoglena shows that the petalonamids were alive and well over 20m years into the Cambrian period and did not go extinct at its outset, as had been thought.

"Even more intriguing, more than 200 fossils of Stromatoveris psygmoglena have now been found, despite the fact that it lacked hard parts which are usually most easily preserved. This indicates that this species was an important member of its shallow marine ecosystem rather than a rare or marginal survivor."

Comment: Still no explanation for the gap in morphology and physiology.