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Bilateran Worm discovered in Precambrian


The Barbarian

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A further demonstration that complex animals evolved long before the Cambrian:

Nature volume 573pages412415 (2019)

Death march of a segmented and trilobate bilaterian elucidates early animal evolution

Abstract

The origin of motility in bilaterian animals represents an evolutionary innovation that transformed the Earth system. This innovation probably occurred in the late Ediacaran period—as evidenced by an abundance of trace fossils (ichnofossils) dating to this time, which include trails, trackways and burrows1,2,3. However, with few exceptions4,5,6,7,8, the producers of most of the late Ediacaran ichnofossils are unknown, which has resulted in a disconnection between the body- and trace-fossil records. Here we describe the fossil of a bilaterian of the terminal Ediacaran period (dating to 551–539 million years ago), which we name Yilingia spiciformis (gen. et sp. nov). This body fossil is preserved along with the trail that the animal produced during a death march. Yilingia is an elongate and segmented bilaterian with repetitive and trilobate body units, each of which consists of a central lobe and two posteriorly pointing lateral lobes, indicating body and segment polarity. Yilingia is possibly related to panarthropods or annelids, and sheds light on the origin of segmentation in bilaterians. As one of the few Ediacaran animals demonstrated to have produced long and continuous trails, Yilingia provides insights into the identity of the animals that were responsible for Ediacaran trace fossils.

 

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1 hour ago, The Barbarian said:

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Interesting to post this. It almost appears like a fossilized fish of some sort. 

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It obviously crawled on legs, because it left a trail with impressions of limbs.  Since it's segmented and has a trilobed structure, it's likely an annelid (many of them had/have legs) or a very primitive arthropod, perhaps a trilobite ancestor.

Genetic and anatomical data have indicated that arthropods evolved from annelids, or possibly they had a common ancestor that was neither.   So something like this was expected to be found.

 

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45 minutes ago, The Barbarian said:

It obviously crawled on legs, because it left a trail with impressions of limbs.  Since it's segmented and has a trilobed structure, it's likely an annelid (many of them had/have legs) or a very primitive arthropod, perhaps a trilobite ancestor.

Ah, yes. Now that you mention this, there do seem to be imprints of back legs at the base of the tail. Trilobites are pretty cool looking too, and I had several small specimens of them years ago. Lost them, unfortunately. 

 

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1 hour ago, BeauJangles said:

Ah, yes. Now that you mention this, there do seem to be imprints of back legs at the base of the tail. Trilobites are pretty cool looking too, and I had several small specimens of them years ago. Lost them, unfortunately. 

They are lovely creatures, particularly the compact ones.    Perhaps the most famous of all fossils.    They are relatively inexpensive, since they were so numerous for so long.   Very nice specimens of common species, go for less than $50 on Ebay, cut out of their matrix.  Replicas go for much less.

 

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