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This Fossil's Penis Worm Mouth Has Mystified Scientists, Until Now

Paleontologists have finally solved the riddle of this ancient creature's sarlacc mouth.
Sarlacc pit. Screenshot: YouTube

In the frigid expanse of northern Greenland, paleontologists unearthed the fossilized remains of some behemoth, wormlike creature. On either side of its meter-long body were 12 short legs, fleshy armor, and spiky antennae that functioned as "arms" for eating.

But the most bizarre feature on this prehistoric chimaera was its monstrous, gaping mouth. Nestled beneath its head, three rows of teeth circled around a terrifying orifice. Sound like something straight out of science fiction? The researchers who recently described the animal thought so, too.

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"The mouth is a spitting image of the Sarlacc from Star Wars," Jakob Vinther, an earth sciences professor at the University of Bristol, said in a statement.

Sarlacc pit from Return of the Jedi. Screenshot: YouTube

Over the course of multiple digs in Sirius Passet, Greenland, Vinther and four other colleagues found several of these specimens, all completely intact. The researchers realized they had discovered the 520 million-year-old remains of Pambdelurion whittingtoni, an extinct ancestor of modern arthropods, which include insects and crustaceans.

But perhaps most excitingly, the team now believes they have also solved a longstanding mystery about the origins of this real-life Sarlacc mouth.

According to their study, which was published this week in Paleontology, a fossilized mouth called Omnidens (literally meaning "one tooth") was discovered in Chengjiang, China two decades ago. Unfortunately, the giant mouth was found without a body, so scientists could only speculate what kind of animal belonged to it.

An artist's rendering of Pambdelurion whittingtoni. Credit: Robert Nicholls, Palaeocreations

In 2006, researchers concluded that Omnidens was a large priapulid, or ocean-dwelling invertebrate like a penis worm, rejecting competing ideas that it belonged to an arthropod or arthropod relative. Still, others suggested the mouth actually existed on Anomalocaris canadensis, a three-foot-long, shrimp-like organism that cruised the Cambrian seas.

Much like fossils themselves, the truth appeared buried by time.

However, Vinther's newly discovered specimens offer a seemingly logical compromise to this debate. Pambdelurion possessed a mouth almost identical to Omnidens, yet it shared many morphological features with arthropods. Because of this, the study's authors propose that Pambdelurion was an ancient relative of Anomalocaris, and also shared a common pre-Cambrian ancestor with Omnidens and modern penis worms.

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Penis worm. Image: Wikipedia/Shunkina Ksenia

"This solves a mystery for the affinities of this giant mouth and demonstrates that the two previous hypotheses—whether the mouth belongs to Anomalocaris or a penis worm—are not exactly right, but not entirely wrong either," Vinther said.

All of these species, with the exception of the penis worm, were alive during the Cambrian Period. At this time in evolutionary history, an explosion of unusual species crawled, swam, and wriggled into existence. Between 570 and 530 million years ago, something contributed to a sudden diversification of life, though scientists aren't sure whether that catalyst was more oxygenated air, the opening up of ecological niches, or some genetic factor that kicked into gear.

Whatever the case, its outpouring resulted in the most unimaginable collection of creatures to ever inhabit Earth.

"It seems as if nowhere was safe back in the Cambrian," said co-author Fletcher Young in a statement. "No matter whether you lived in the water column or on the seafloor there was a big, ugly beast that would devour you."

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