The missing fossils argument; new very early Ediacaran (Introduction)

by David Turell , Monday, November 18, 2024, 21:43 (2 days ago) @ David Turell

A worm with an external skeleton:

https://www.sciencedaily.com/releases/2024/11/241118125212.htm

"The history of a major animal group, composed of millions of species of insects, arachnids, and nemotodes, has been elusive -- until now. A team has now identified the oldest known ecdysozoan in the fossil record and the only one from the Precambrian period.

"Until recently, details about this group's most distant past have been elusive. But a UC Riverside-led team has now identified the oldest known ecdysozoan in the fossil record and the only one from the Precambrian period. Their discovery of Uncus dzaugisi, a worm-like creature rarely over a few centimeters in length, is described in a paper published today in Current Biology.

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"This discovery reconciles a major gap between predictions based on molecular data and the lack of described ecdysozoans prior to the rich Cambrian fossils record and adds to our understanding of the evolution of animal life," said Mary Droser, a distinguished professor of geology at UCR, who led the study.

"The ecdysozoans are the largest and most species-rich animal group on Earth, encompassing more than half of all animals. Characterized by their cuticle -- a tough external skeleton that is periodically shed -- the group comprises three subgroups: nematodes, which are microscopic worms; arthropods, which include insects, spiders, and crustaceans; and scalidophora, an eclectic group of small, scaly marine creatures.

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"Ediacaran animals, which lived 635-538 million years ago, were ocean dwellers; their remains preserved as cast-like impressions on the seabed that later hardened to rock. Hughes said uncovering them is a labor-intensive, delicate process that involves peeling back rock layers, flipping them over, dusting them off, and piecing them back together to get "a really nice snapshot of the sea floor."

"This excavation process has only been done at Nilpena Ediacara National Park in South Australia, a site Droser and her team have been working at for 25 years that is known for its beautifully preserved Ediacaran fossils.

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"'Because it was deep, we knew it wasn't smooshed easily so it must have had a pretty rigid body," Hughes said. Other defining characteristics include its distinct curvature and the fact that it could move around -- seen by trace fossils in the surrounding area. Paul De Ley, an associate professor of nematology at UCR, confirmed its fit as an early nematode and ruled out other worm types.

"'At this point we knew this was a new fossil animal and it belong to the Ecdysozoa," Hughes said.

"The team called the new animal Uncus, which means "hook" in Latin, noting in the paper its similarities to modern-day nematodes. Hughes said the team was excited to find evidence of what scientists had long predicted; that ecdysozoans existed in the Ediacaran Period."

Comment: this is the first animal like Ediacaran fossil I've seen. Non e of the others seemed to be mobile. Also it appears de novo as do the Cambrian animals.