Cretaceous Snail Fossilized In Amber Right After Giving Birth

New-born baby snails were encased in amber 99 million years ago and have now greatly expanded our knowledge of Cretaceous gastropods. Image Credit: Tingting Yu

A snail that lived alongside the dinosaurs has been found, imprisoned in amber for 99 million years, providing us with unprecedented detail of such an ancient mollusks anatomy. Even better for science – although worse for the snail – it had just given birth, and at least some of its newborns were close enough to be encased in the same lump of amber.

Snails seldom preserve well, so most of what we know of their history comes from shells, or at best imprints outlining the shape of their bodies, although one partially preserved Cretaceous specimen in amber has been found. Consequently, the discovery of a superbly preserved snail would be remarkable enough, even if it was not accompanied by five recently born young. The youngest was still connected by a trail of mucus to the mother.

"The snails were apparently encased in the tree resin immediately after birth and preserved in that position over millions of years. The mother snail must have noticed her impending fate and is stretching her tentacles up in a 'red alert' posture," Dr Adrienne Jochum of Senckenberg Research Institute said in a statement. Quite why even a member of the notoriously slow gastropod class couldn't escape an encroaching sapslide is unknown, but perhaps she was tired after the birth process. As the accompanying photographs show, the amber is clear enough to provide an excellent view, but Jochum and colleagues also applied CT scans to study the unfortunate family's innards.

The mother snail and her young, marked with numbers. Image Credit: Tingting Yu

Simply the fact the snail gave birth to live young is a significant finding. A few land snails today have live young, and we have a record of this from 19 million years ago, but egg-laying is far more common. It's possible the same was true in the Cretaceous, but a single contradictory data point throws that into question. This is the oldest evidence of viviparity (live birth) we have found among snails.

Jochum and colleagues have named the amber-encased species Cretatortulosa gignens in the journal Gondwana Research. They suspect live birth was an adaptation to protect the young against predators, although how a snail that couldn't even avoid an amber avalanche did that is less clear. We also don't know why this strategy might have been more advantageous for gastropods then than now.

"Just like their modern relatives from the genus Cyclophoroidea, our new discovery probably spent its life inconspicuously on dead and rotting leaves. We assume that the young of this species – compared to egg-laying snails – were smaller and lower in number to increase their chance of survival." Jochum said.

The discovery was made in a northern Myanmar amber mine. Although Myanmar is now considered part of South-East Asia, which had been part of the supercontinent Laurasia, the western part of the country lies on the Indian tectonic plate. At the time this snail lived, the Indian plate was breaking loose from Gondwana and beginning its long journey north to unite with Asia.

A CT scan of the snail, one of its young, and the amber in natural light. Image Credit: Tingting Yu

 


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