Nature is weird and wonderful. And, yet, sometimes a newly discovered organism can be too weird. In 1977, when Simon Conway Morris found one such creature, he thought he must be hallucinating. Appropriately, he named it Hallucigenia.
For the last 40 years, the many well-preserved fossils of Hallucigenia sparsa—its full name—have been studied intensely by a small group of biologists. Until now they couldn’t, quite literally, make head or tail of Hallucigenia. But with the help of electronic microscopes, as described in a study in Nature, Martin Smith at Cambridge University and his colleague Jean-Bernard Caron at the University of Toronto, have figured out which way the head goes.
Those nerdy details are not as trivial as you may think. Hallucigenia has been, as paleontologist Xiaoya Ma describes here (paywall), one of the most celebrated organisms from a special period 540 million years ago. That period, often called the Cambrian explosion, is thought to have brought a sudden burst of biodiversity on Earth and many animals here today have ancestors dating back to that time. Studying Hallucigenia has shown that evolution in that period didn’t happen in leaps, but in small increments.
Hallucigenia‘s modern descendants are pretty weird too. One, the penis worm—so-called because it resembles a man’s genitalia—gained the mouth teeth that belong to Hallucigenia but evolved to turn them inside out when it wanted. Another, the velvet worm—which has velvet-like skin—gained the throat teeth which appear on legs inside its jaw.
Although Smith and Caron have solved one of Hallucigenia‘s mysteries, they have yet to understand exactly how its descendants evolved. But such is nature’s game that both a cute, cuddly velvet worm and a vaguely pornographic penis worm can be descendants of a ghoulish creature.