Scientists have revealed insights into a peculiar, phallus-shaped creature discovered at a fossil site in Canada.
The animal has been identified as Spartobranchus tenuis, a species from the Cambrian period that was previously unknown to science.
The odd-looking creature was an ancient relative of acorn worms that exist today, according to researchers.
Their study, published in the journal Nature, is the first full description of the prehistoric animal.
Remains of soft-bodied worms were found in the Burgess Shale fossil beds in Yoho National Park, British Columbia, Canada throughout the last century.
But now researchers studying the 505 million years old fossils have for the first time given a detailed insight into the lives of the bizarre beasts.
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.
The animals' phallus-shaped anatomy consisted of a head, or "muscular proboscis", in front of a short "collar" and ended with "a posterior kind of long wormy tail which has gill slits", Dr Cameron explained. The body ended in a bulbous structure which may have helped it anchor to the sea bed.
The team's identification of Spartobranchus tenuis pushes the appearance of enteropneusts (or acorn worms) in the fossil record back a further 200 million years to the Cambrian period (545 to 495 million years ago). Previously, the oldest specimens found were from the later Triassic period (248 million to 205 million years ago).
Crucial missing linkAccording 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 indicates 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.
"By finding enteropneusts in tubes we begin to bridge this evolutionary gap," Dr Morris told BBC Nature.
Dr Cameron commented: "It's astonishing how similar Spartobranchus tenuis fossils are to modern acorn worms, except that they also formed fibrous tubes."
In many of the fossils, remains of the worms were encased in these tubes, and the team believe they lived in the structures and may have even sealed themselves in a doughnut shape within the tubes.
Spartobranchus tenuis fossils are unique to the Burgess Shale fossil bed in Canada's Yoho National Park, which is known for its preservation of soft-bodied animals from the Cambrian period.
Prof Morris added that the team's identification of the new species at the site "reinforces the magnitude of the Cambrian 'explosion', with many of the major [animal] groups evolving relatively rapidly".
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Source: http://www.bbc.co.uk/nature/21745029
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