From the mouths of molluscs -- ancient snail relative found

Aug 22, 2012
Two snails cross a wooden veranda in Oberbeuren, southern Germany. Fossils of toothy, slug-like creatures that grazed the sea floor 500 million years ago have shed light on the origins of modern-day snails, shellfish and squid, a study said Wednesday.

Fossils of toothy, slug-like creatures that grazed the sea floor 500 million years ago have shed light on the origins of modern-day snails, shellfish and squid, a study said Wednesday.

The most comprehensive analysis yet of the ancient slugs' mouth parts -- multiple rows of that moved in conveyor-belt fashion, showed they were related to present day molluscs, scientists wrote in the journal .

Dubbed Wiwaxia and Odontogriphus, the slugs' place on the evolution ladder has been in contention for decades -- whether they were early molluscs, relatives of the earthworm, or a completely different species that died out.

This is a reconstruction of the Odontogriphus mouthparts. Credit: Marianne Collins 2012

Using new microscope technology, Martin Smith, a graduate student at the University of Toronto's department of , found they shared a feeding mechanism with today's molluscs.

"Their mouthparts are... the closest thing that we have to the radula, the conveyor-belt-like feeding apparatus found in almost all molluscs today," he told AFP.

"My new reinterpretation of their 'teeth' shows that they represented early molluscs."

Molluscs, which also include octopuses, mussels and oysters, are the second-biggest , yet little has been known about their early evolution.

Fossil of Wiwaxia, mouthparts are visible towards front. Credit: Martin Smith

Odontogriphus, whose name means "toothed riddle" in Greek, was a naked slug that grew up to 15 centimetres (six inches) long, while tiny Wiwaxia, between 1 millimetre and 5 cm, was covered with spines and scales.

The invertebrate fossils come from the Burgess Shale Formation in the Canadian province of British Columbia, deposited there during the Middle Cambrian period about 505 million years ago.

To study the remains, Smith used an which has a resolution about a thousand times better than that of a , "so you see loads more detail" of the mouth parts.

It has only recently become possible to put large fossils in electron microscopes without damaging them.

This is an electron micrograph of Wiwaxia mouth parts seen in Figure 2. Credit: Martin Smith

The researcher concluded that the mouths of Wiwaxia and Odontogriphus had two to three rows of 17-33 teeth of a similar size, with a symmetrical central tooth and more, smaller teeth on the edges.

The teeth would have moved around a tongue in the same way as those of both plant- and meat-eating molluscs today, scooping algae and organic waste from a muddy sea floor.

"I don't see how you can doubt that they are molluscs any more," said Smith.

What is not clear is whether these fossils were the direct ancestors of today's molluscs.

There were likely several similar-looking species living alongside Wiwaxia and Odontogriphus, but since species cannot interbreed, only one could have given rise to the snails and slugs we know today.

"It's possible that Odontogriphus or Wiwaxia was this species, but it's more likely that they were very close relatives -- offshoots from the lineage that would have led to all molluscs," said Smith.

Explore further: 110-million-year-old crustacean holds essential piece to evolutionary puzzle

add to favorites email to friend print save as pdf

Related Stories

Danger lurking below the sand

Aug 01, 2011

A voracious predator that devours prey larger than itself has been found lurking beneath Queensland's golden sandy beaches.

500 million year old fossils discovered on new site

Sep 17, 2010

During an expedition into the Canadian Rocky Mountains in 2008, a Canadian-led team including Swedish researchers from Uppsala University found a new site with exceptionally preserved fossils. The site and ...

Recommended for you

Fish eye sheds light on color vision

Dec 23, 2014

A fish eye from a primitive time when Earth was but one single continent, has yielded evidence of color vision dating back at least 300 million years, researchers said Tuesday.

Study sheds new light on the diet of extinct animals

Dec 22, 2014

A study of tooth enamel in mammals living today in the equatorial forest of Gabon could ultimately shed light on the diet of long extinct animals, according to new research from the University of Bristol.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.