Who knows what nightmares inspired George Lucas to create the Sarlacc in Return of the Jedi, but what he came up with looks like a giant version of a mouth that haunted the oceans 520 million years ago.
Pambdelurions whittingtoni was a fearsome Cambrian predator, related to modern arthropods like insects and crustaceans. Although not the largest hunter of the times, the combination of eleven pairs of legs to walk across the ocean bottom and eleven swimmers to allow them to move through the waters above, they would have been more than a match for most of the species of the day.
But although Pambdelurion has been known for decades, it is only now, with a study of several hundred Pambdelurion fossils from the northern tip of Greenland, Sirius Passet, that we know what sort of mouth it had.
The fossil imprint of the mouth on a 520 million-year-old Pambdelurion whittingtoni. Fletcher Young
Vinther is first author of a paper in Paleontology describing the Pambdelurion mouthparts. Although most of the Greenland specimens are incomplete, four are preserved in what Vinther calls “reasonable detail”. Differences in the mouths' locations suggest it sat on the end of a cone that could be moved around to capture prey.
Mouths like this have been seen before among Cambrian fossils, but paleontologists have been confused about what creatures possessed them. Vinther's discovery suggests they were actually widespread, and probably evolved in an early ancestor of many of the Cambrian species.
The mouth was made up of teeth-like sclerites (hardened body parts) and circles of radial plates bearing rounded nodules. Larger versions of the same mouth, found in China and called Omnidens, came from fossils where little else had been preserved, leading to debate about what sort of creature possessed it.
Favored options included the mud-dwelling marine worms known as penis worms (for obvious reasons) and the free swimming apex predator Anomalocaris. Some Omnidens were so large their owners were thought to have been 2 meters (6.6 feet) long, gigantic at the time.
A modern penis worm, Priapulus caudatus, whose ancestors go back to the Cambrian era. Jakob Vinther and Fredrik Pleijel
The largest of Vinther's complete Pambdelurions was 46 centimeters (1.5 feet) long, although partial fossils suggest some grew to 55 centimeters (1.8 feet). Assuming similar mouth-to-body ratios, Vinther calculates the original Chinese Omnidens came from individuals 1.5 meters (5 feet) in length – not quite as large as some had speculated, but still the largest mobile Cambrian creatures we know.
“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. It seems these mouths, so strange looking to our eyes, were a common feature in the Cambrian originating with an ancestor from which these very different species descended.
Another image of a fossilized Pambdelurion whittingtoni from the Sirius Passet, Greenland, Fletcher Young