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When researchers studied the first known fossils of Prototaxites more than a century ago, they assumed the remains came from a tree. Decades of study eventually led paleontologists to rule out plants, pointing instead to a giant fungus. Now, a new study has reopened the mystery.
Neither plant nor fungus. The study has reignited debate over the nature and taxonomy of Prototaxites, prehistoric organisms once widely considered fungi. Removing these creatures from the fungal evolutionary branch suggests they may have belonged to an extinct and unknown group in the tree of life.
400 million years ago. What experts do know from the fossil record is that Prototaxites lived during the middle of the Paleozoic Era, between 420 million and 375 million years ago. These organisms had a cylindrical, trunk-like shape and could grow up to 26 feet tall with a diameter of about 3 feet. Their size and age make them some of the earliest large organisms ever recorded.
Scientists reached a consensus in the mid-2000s that these organisms didn’t get their carbon from photosynthesis, like plants, but from other living things, as fungi do.
Rhynie Chert. The new study challenges that conclusion. It focuses on one species, Prototaxites taiti, using fossils found at the Rhynie Chert site in Scotland. This site contains fossilized remains of P. taiti, fungi, and other organisms from different biological kingdoms.
Similarities and differences. The fossil analysis revealed some expected similarities with fungal structures. P. taiti had internal tubular features, but they branched and connected in ways that differ from known fungi. That wasn’t the only surprise.
Researchers found no evidence of chitin, the compound in the cell walls of all modern fungi and also present in ancient fungi. Instead, the chemical signature resembled that of lignin, a polymer found in vascular plants.
The study appears in draft form in the bioRxiv preprint repository and hasn’t yet undergone peer review.
So what? That detail means any conclusions should be treated with caution. Still, the research team outlined its preliminary findings in the draft study.
They wrote: “We conclude that the morphology and molecular fingerprint of P. taiti is clearly distinct from that of the fungi and other organism preserved alongside it in the Rhynie chert, and we suggest that it is best considered a member of a previously undescribed, entirely extinct group of eukaryotes.”
Image | Matthew Humpage, Northern Rouge Studios
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