Penis-Shaped Worm Creature Solves Ancient Fossil Mystery

Fossilized forms of a penis-shaped invertebrate have shed light on a dramatic spurt in Earth's biodiversity and may be the missing link connecting two mysterious branches of sea creatures, Canadian scientists reported on Wednesday.

Christopher Cameron of the University of Montreal's Department of Biological Sciences and his colleagues unearthed the phallus-shaped fossil in Canada's 505 million year-old Burgess Shale. The discovery is resetting the origin of these enteropneusts back to the Cambrian period. The study was published on Wednesday in the journal Nature.

The prehistoric marine creatures were around the size of an earthworm, "but unlike an earthworm that's segmented from its front end to its back end, these guys just had three distinct body segments," said research team member Dr Christopher Cameron from the University of Montreal, Canada.

 "Unlike animals with hard parts including teeth, scales and bones, these worms were soft-bodied, so their fossil record is extremely rare," said Dr. Cameron added. "Our description of Spartobranchus tenuis, a creature previously unknown to science, pushes the fossil record of the enteropneusts back 200 million years to the Cambrian period, fundamentally changing our understanding of biodiversity from this period."

According to Dr Cameron and colleagues, Spartobranchus tenuis reveals a crucial evolutionary link between two distinct living groups of animals: enteropneusts and pterobranchs.

Both groups belong to the hemichordates phylum of marine animals, the origins of which has intrigued scientists since its discovery in the 19th Century.

"Enteropneusts look very different from pterobranchs in as much as the former are worms, whereas the latter are tiny animals, live in tubes, are colonial and have feeding tentacles," explained Professor Simon Conway Morris from the University of Cambridge, UK, who also worked on the study.

The new research shows that Spartobranchus tenuis was an ancient relative of both groups of animals. It shared many of the features of modern acorn worms but like pterobranchs, lived in a tube.