Cretaceous amber fossils highlight the evolutionary history and morphological conservatism of land snails

Abstract

Other than hard bones and shells, it is rare for soft tissues to fossilize, but occasionally they are well-preserved in amber. Here, we focus on both modern and fossilized species of the land snail superfamily Cyclophoroidea. Phylogenetic relationships within the Cyclophoroidea were previously studied using extant species, but timing of divergence within the group remains unclear. In addition, it is difficult to observe morphological traits such as the chitinous operculum and periostracum of fossil snails due to their poor preservation potential. Here we describe nine species including a new genus and five new species of well-preserved fossil cyclophoroideans from the mid-Cretaceous Burmese amber. These fossils include not only the shell, but also the chitinous operculum and periostracum, soft body, and excrements. We present the first estimation of divergence time among cyclophoroidean families using fossil records and molecular data, suggesting extreme morphological conservatism of the Cyclophoroidea for nearly 100 million years.