This Gnarly Ancient Creature Had Spiny Teeth in Its Guts

A fossil of a strange, squishy creature with a toothy tongue inside its gut has been discovered in good condition.

The specimens of this bizarre mollusk-like creature were found in the Carboniferous Bear Gulch Limestone deposit in Montana and were unusually well-preserved, according to a paper published in the journal Biology Letters.

This species, named Typhloesus, was thought to have lived during the Carboniferous period, between 358.9 million and 298.9 million years ago. Although it was previously identified, it has not been classified into any one group of animals because of a lack of fossil details.

The Carboniferous era is associated with rich coal deposits in its fossil rock layers. According to the University of California Museum of Paleontology, in Berkeley, the amniote egg (with a shell) was one of the greatest evolutionary advances during the period, which allowed the ancestors of birds, mammals and reptiles to reproduce on land. Oceans were often warm and shallow, and they were dominated by sharks and bony fishes after the late Devonian extinction, as well as starfish, gastropods, sea urchins and many other marine invertebrates.

"Here, we document new features, including possible phosphatized muscle tissues and a hitherto unrecognized feeding apparatus with two sets of ca. 20 spinose teeth whose closest similarities appear to lie with the molluscan radula," the authors wrote in the paper. "Typhloesus may represent an independent radiation of Mid-Palaeozoic pelagic gastropods."

The key discovery in this new specimen is a "radula-like organ" in the creature's foregut, with two rows of spiny teeth. Radulas are structures that mollusks like snails use to grind down their food.

"Identification of the toothed feeding apparatus throws further light on the functional anatomy of Typhloesus, and potentially its wider relationships," the authors said. "The location of the teeth in the posterior section of the foregut, as well as their direction of curvature, suggests that to function effectively most of the foregut would have had to evert in order to bring the teeth into a position to seize prey."

In essence, rather than swallowing prey and using the tooth-like tongue apparatus inside the gut, this creature everted the tongue outside of its body to eat its prey.

Images of the ancient sea creature called Typhloesus: the fossil itself (bottom) compared with a simplified illustration (top). The spiny radula-like organ is shown in orange. Dr Simon Conway Morris / Jean-Bernard Caron / Biology Letters / Royal Society

"Eversion of the foregut would most likely have been achieved by a hydrostatic mechanism whereby the foregut was enclosed in a fluid-filled body cavity," the authors said.

This mechanism can be seen in other animals, both ancient and modern, and some notable examples are starfish and sea cucumbers. The mechanism usually requires the contraction of muscles to evert the gut, which is also supported by the findings of a "paired structure close to the foregut–midgut boundary" in the Typhloesus specimen. However, according to the authors, the structure may have had some other function.

"We are mindful that jaws are rampantly convergent [traits that evolved to look similar despite having distant genetic ties, like wings in bats and bees] and radularlike structures occur elsewhere," the authors wrote.

"We conclude that a place for Typhloesus among the gastropods is plausible, but acknowledge that similarities to the molluscs, let alone the heteropods [sea slugs and sea elephants], may be the result of convergence," the authors said.

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A stock image shows ancient sea life from the Cambrian Period. iStock / Getty Images Plus

Further soft-bodied samples from this era are needed to form a more solid conclusion about Typhloesus' place in the evolutionary tree. But because of the immense amount of time that has passed since they lived, not many well-preserved specimens are available, let alone any discoveries.

"More precise pronouncements of its [evolutionary] relationships are hampered by the unique aspects of its morphology and the sparsity of equivalent soft-bodied fossils in Palaeozoic deposits," the authors wrote in their paper.