The oldest traces of a digestive tract discovered in cloudinid fossils

Cloudinid fossils
Cloudinid fossils

An article published in the journal “Nature Communications” reports a study of fossils of organisms belonging to the group of cloudinids that show the oldest traces of a digestive tract. A team of researchers led by the paleobiologist James Schiffbauer of the University of Missouri subjected fossils discovered in Nevada dating back to about 550 million years ago to a micro-CT scan that allowed to recreate a 3D image thanks to which it was possible to examine their internal parts. Among the anatomical structures there’s also a primitive digestive tract, a discovery that helps to understand something more about the relationships between the large groups of today’s animals.

Cloudinids, organisms that are part of a taxonomic family that includes the genera Cloudina, Acuticocloudina and Conotubus, lived between the Ediacaran and Cambrian periods. These tiny beings with a length that could reach 15 millimeters, were composed of conical structures inserted into each other forming a body that was perhaps flexible. The overall appearance of these creatures remains unknown and it’s unclear how well known fossils are representative of that appearance, despite having been found all over the world. They aren’t associated with the so-called Ediacara biota existing at that time, with organisms of very strange shapes, but the classification of cloudinids is also under discussion.

Unlike the strange organisms of the Ediacara biota, of which paleontologists sometimes don’t know if they’re animals, plants or something else, cloudinids are normally considered animals and discussions begin when they start talking about relationships with large taxonomic groups. In general, a process called pyritization preserved their soft tissues after death by creating a fossil cast. However, fossils were discovered in Nevada in which pyrite hasn’t filled these organisms’ inner tube allowing to see the internal soft tissues.

Taking advantage of this peculiarity of fossil cloudinids dated between 539 and 550 million years ago, the team led by James Schiffbauer subjected them to micro-CT scans, a non-invasive examination derived from the common medical CT scan which has the advantage of being able to irradiate the fossils far more than human patients. It’s a type of examination used increasingly in the field of paleontology because it allows to obtain 3D reproductions of the organisms examined without damaging them. Those reproductions offer the possibility to study the internal details of organisms that sometimes would be impossible to see without destroying the fossils.

The top image (Courtesy James Schiffbauer et al.) shows some cloudinid fossils discovered in Nevada. The bottom image (Courtesy James Schiffbauer et al.) shows a 3D reproduction of a 550 million year old fossil with the tubular structure on the left in red and the internal digestive tract in gold, on the left inside the structure and isolated on the right.

An article published in September 2017 in the journal “PLOS ONE” described a research on primitive trilobites with the discovery of the oldest digestive tract consisting of both digestive glands and a crop. The tract discovered in cloudinid fossils was probably much more basic therefore the relationship with arthropods is to be evaluated. The researchers speculate that cloudinides may have been part of the annelid (Annelida) phylum but we may be far from a final classification. However, it’s a step forward made with the help of modern technologies.

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