When it was just giving birth to its young, the small land snail was caught in a drop of tree resin and preserved along with its offspring for millions of years. Researchers report on a 99 million year old amber that preserved the house and the soft tissues of a snail including its offspring. The scene, frozen to stone, documents that some land snails were viviparous as early as the Cretaceous, say the scientists.
Some ambers are paleontological jewels: the petrified tree resin has already given scientists many interesting insights into the history of life. What is special about this is that resin can also preserve sensitive living beings and filigree structures, sometimes in astonishing detail: insects, fungi, feathers, soft tissues and many other traces of former living beings have been discovered in amber by scientists in recent years. Since the animals were mostly caught surprisingly by the tree sap and torn from life, in some cases scenes have also been preserved that allow conclusions to be drawn about abilities and behavior.
Snail with newborn babies
This is now also the case with the amber that the researchers working with Adrienne Jochum from the Senckenberg Research Institute and Museum of Nature and the Museum of Natural History in Bern report on. It comes from an amber mine in northern Myanmar, where there was a lush tropical forest 99 million years ago, in which it apparently crawled and flickered intensely next to the dinosaurs. As can be seen quite clearly, the amber contains a screw-shaped snail shell about eleven millimeters long. The researchers hoped that the animal’s soft tissues were also preserved, so they examined the fossil using high-resolution photography and micro-computed tomography images.
They discovered the soft body structures of the snail as well as traces of mucus. “Our new amber find is remarkable for this reason alone,” explains Jochum. But there was still more to discover: “In addition to the body and shell of the land snail, we found five freshly born young of the apparently female snail.” The photos show the tiny bodies as well as the still transparent structures of their delicate houses. “The ensemble was apparently enclosed by the tree sap immediately after birth and preserved in this position for millions of years,” says Jochum. The mother snail raised its antennae when it was surrounded by the resin, as the photos show. She probably noticed her impending fate and was therefore highly active, explains the scientist.
Already viviparous in the Cretaceous period
The snail is a previously unknown species – but above all, the discovery now represents the oldest evidence of a live birth in land snails, say the scientists. “Based on the find, we can not only make statements about the morphology and paleoecology, but now also know that there were viviparous snails in the Cretaceous”, says Jochum happily. Some of today’s species also reproduce in this way, but so-called viviparity is more of an exception in this group of molluscs. The researchers suspect that the species, newly described as Cretatortulosa gignens, gave birth to its young alive, because egg clusters in the tropical forests of the Cretaceous period were probably looted particularly frequently by predators.
“Just like its modern relatives from the genus Cyclophoroidea, our snail probably spent its life inconspicuously on dead and rotting leaves. We assume that these snails produced smaller and fewer young animals than the hatchlings of egg-laying snails, ”says Jochum. The bottom line is that the protection provided by carrying eggs and the subsequent live birth was apparently a decisive advantage for the survival of the offspring of this little cretaceous snail.
Source: Senckenberg Research Institute and Nature Museums, specialist article: Gondwana Research, doi: 10.1016 / j.gr.2021.05.006