A sweeping evolutionary analysis of nearly 700 genera has redrawn the family tree of Neogastropoda, one of the most diverse and ecologically important groups of marine snails. The study provides the strongest evidence yet that the order arose from a single common ancestor, rather than representing a collection of unrelated lineages that merely evolved similar lifestyles. It also introduces four new families and identifies a previously overlooked burst of diversification in the early Cenozoic, a period when marine ecosystems were being radically reshaped after the end-Mesozoic extinction crisis. Together, the findings offer a new framework for understanding how thousands of predatory and scavenging snails evolved, survived environmental upheaval and became one of the most species-rich branches of marine molluscs.
Neogastropoda includes approximately 16,000 formally recognised species, although the true number is likely considerably higher. Its members inhabit almost every marine environment, from shallow tropical reefs and tidal flats to deep-sea habitats, and display an extraordinary range of shell shapes, feeding strategies and body forms. Some are active predators equipped with venom or specialised drilling structures, while others consume carrion or small organisms on the seafloor. Their shells are often spectacular, but appearance alone has made classification difficult. Closely related species can look dramatically different, while unrelated species may evolve similar shells in response to comparable environmental pressures. This combination of evolutionary diversity and morphological convergence has left major questions about relationships within the group unresolved for decades.
To address the problem, researchers from the Swedish Museum of Natural History and institutions around the world combined traditional systematics with modern phylogenomics. Their analysis drew on specimens preserved in natural history collections, including material gathered across different oceans and habitats. Rather than relying on a small number of visible characteristics, the team compared large quantities of genetic information from hundreds of species. Phylogenomics uses genome-scale or transcriptome-scale molecular data to estimate evolutionary relationships by identifying DNA sequences inherited from common ancestors. When many independent genetic markers support the same branching pattern, researchers can distinguish genuine ancestry from similarities produced by convergent evolution. The resulting dataset represents one of the broadest attempts to reconstruct the evolutionary history of Neogastropoda.
The new phylogenetic tree indicates that the diverse groups currently assigned to Neogastropoda share a single evolutionary origin. In evolutionary terms, this means the order is monophyletic: all of its recognised members descend from one ancestral lineage, and no major group traditionally placed outside the order needs to be added to explain its history. Establishing monophyly is more than a matter of nomenclature. It determines how scientists interpret the evolution of key traits, including carnivory, shell construction, reproductive biology and sensory systems. If a feature evolved once in a common ancestor, its later distribution may reflect inheritance and modification. If it evolved repeatedly, researchers must instead identify the separate ecological pressures that produced similar outcomes.
The analysis also supports a revised classification containing four newly recognised families. These changes are significant because taxonomic families provide the structure scientists use to organise biodiversity and communicate about it. A stable classification helps researchers identify whether an unusual specimen represents a new species, a previously overlooked member of a known lineage or a representative of an entirely distinct branch. This is especially important in Neogastropoda, where many species are small, rare, cryptic or found in poorly sampled marine environments. By placing species into a more reliable evolutionary context, the new framework can guide future collecting, genetic comparisons and formal descriptions. It may also help reveal hidden diversity that traditional shell-based classifications have missed.
The study changes the timeline of neogastropod evolution as well. Earlier interpretations linked the rise of the group mainly to major marine changes near the end of the Mesozoic Era, around the time non-avian dinosaurs disappeared. The researchers’ reassessment of the fossil record, combined with molecular dating and the new phylogeny, points to an additional evolutionary acceleration during the early Cenozoic, specifically the Danian stage. This interval began immediately after the end-Cretaceous mass extinction, when marine food webs and predator communities were undergoing rapid transformation. The result suggests that the modern diversity of Neogastropoda was not produced by one uninterrupted expansion, but by multiple phases of innovation and replacement separated by major ecological disruptions.
One possible explanation involves a new generation of shell-crushing predators. During the early Cenozoic, crustaceans and cephalopods capable of attacking and breaking mollusc shells became increasingly important in marine ecosystems. Such predators would have imposed intense selection on snails, favouring shells that were thicker, stronger or architecturally more resistant to compression and drilling. In evolutionary terms, this is an example of predator-driven natural selection: individuals with traits that reduce the probability of being eaten are more likely to survive and reproduce. Lineages unable to withstand the new threats may have declined or gone extinct, while others diversified into forms with reinforced shells, altered apertures or different internal structures. The modern neogastropod families may therefore represent descendants of survivors that passed through a severe evolutionary filter.
This scenario does not mean that shell strength alone determined the outcome. Evolutionary radiations are shaped by interacting pressures, including prey availability, temperature, ocean chemistry, habitat complexity and competition. A stronger shell may improve defence but also require more energy to build, reduce mobility or limit the habitats an animal can occupy. Neogastropods may have responded through a combination of shell redesign, changes in behaviour, improved sensory systems and more specialised feeding mechanisms. The phylogenetic results allow scientists to map these traits onto the evolutionary tree and test whether they appeared once, evolved repeatedly or were lost in particular lineages. Such comparisons can reveal whether diversification followed a common adaptive pattern or emerged through many independent experiments in marine survival.
The findings also demonstrate why natural history collections remain essential in the genomic age. Museum specimens preserve a physical record of biodiversity that can span centuries, including species from locations that are now difficult to access or environmentally transformed. When suitable tissue is available, DNA can be extracted from preserved material and combined with anatomical observations, locality data and fossil evidence. This integration makes it possible to study organisms that would otherwise be absent from large-scale analyses. For Neogastropoda, collections provided the taxonomic breadth needed to compare nearly 700 genera and connect living species with the fossil record. The study shows that systematics is not simply the naming of organisms; it is a data-rich science capable of revealing how entire branches of life responded to planetary change.
Despite the scale of the analysis, the evolutionary story of Neogastropoda is far from complete. Thousands of species remain undescribed, and many known species have never been sampled genetically. Deep-sea communities, remote coastlines and small-bodied snails are likely to contain especially important gaps. As additional specimens and molecular data become available, researchers will be able to refine the new classification, improve estimates of the timing of evolutionary events and test the role of predation in shaping shell diversity. For now, the study provides a powerful map of one of the ocean’s most successful radiations. It shows that the familiar shells collected on beaches are not isolated curiosities, but surviving evidence of a complex history involving extinction, innovation and repeated bursts of evolution across hundreds of millions of years.
Subject of Research: Animals
Article Title: Phylogeny, classification, and evolutionary history of Neogastropoda.
Web References: https://doi.org/10.1093/zoolinnean/zlag058
References: Zoological Journal of the Linnean Society; DOI: 10.1093/zoolinnean/zlag058
Image Credits: Alexander Fedosov
Keywords: Neogastropoda, marine snails, phylogenomics, evolutionary biology, molluscs, biodiversity, natural history collections, taxonomy, shell evolution, Cenozoic diversification, marine predators, evolutionary radiation
