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Stasis: Early trilobites had stomachs, contrary to earlier assumptions

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digestive system preserved as reddish iron oxides/F. Chen

From ScienceDaily:

Exceptionally preserved trilobite fossils from China, dating back to more than 500 million years ago, have revealed new insights into the extinct marine animal’s digestive system. Published today in the journal PLOS ONE, the new study shows that at least two trilobite species evolved a stomach structure 20 million years earlier than previously thought.

“Trilobites are one of the first types of animals to show up in large numbers in the fossil record,” said lead author Melanie Hopkins, an assistant curator in the Division of Paleontology at the American Museum of Natural History. “Their exoskeletons were heavy in minerals, and so they preserved really well. But like all fossils, it’s very rare to see the preservation of soft tissues like organs or appendages in trilobites, and because of this, our knowledge of the trilobite digestive system comes from a small number of specimens. The new material in this study really expands our understanding.”

Previous research suggests that two body plans existed for trilobite digestive systems: a tube that runs down the length of the trilobite’s body with lateral digestive glands that would have helped process the food; or an expanded stomach, called a “crop,” leading into a simple tube with no lateral glands. Until now, only the first type had been reported from the oldest trilobites. Based on this, researchers had proposed that the evolution of the crop came later in trilobite evolutionary history and represented a distinct type of digestive system.

The Chinese trilobite fossils, about 20 percent of which have soft tissue preservation, are dated to the early Cambrian, about 514 million years ago. Contradictory to the previously proposed body plans, the researchers identified crops in two different species within this material. In addition, they found a single specimen that has both a crop and digestive glands — suggesting that the evolution of trilobite digestive systems is more complex than originally proposed.

“more complex than originally proposed.” Right… Less time for purely Darwinian processes to work.

“This is a very rigorous study based on multiple specimens, and it shows that we should start thinking about this aspect of trilobite biology and evolution in a different way,” Hopkins said. Paper. (public access) – Melanie J. Hopkins, Feiyang Chen, Shixue Hu, Zhifei Zhang. The oldest known digestive system consisting of both paired digestive glands and a crop from exceptionally preserved trilobites of the Guanshan Biota (Early Cambrian, China). PLOS ONE, 2017; 12 (9): e0184982 DOI: 10.1371/journal.pone.0184982 More.

“we should start thinking about this aspect of trilobite biology and evolution in a different way” We hear you. So do lots of people. Great find.

Right now, the field could do with a shot of analyzable dinosaur soft tissue as well…

See also: Trilobite “behaviorally sophisticated”

Food for thought from that paywalled soft dino tissue article in Science (They are obviously stepping around the implications of such finds for what we can really know about now-extinct life forms. The market in career-boosting speculation is bound to take a tumble.)


Stasis: Life goes on but evolution does not happen

Yeah, ok, but could they stomach critical rationalism? Was Neo-Darwinism digestible, or did it just pass right through? Mung
Good post. I'm sure a/mats will find a way to fit this into their just-so story called Darwinian evolution. It's what they do. Truth Will Set You Free
Contrary to earlier assumptions, they ain't seen nothin' yet. :) Dionisio

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