One-Of-A-Kind Jurassic Sea Creature With Enormously “Long Neck” Discovered After Nearly 50 Years in Museum Storage

A study published in PeerJ by paleontologists Sven Sachs and Daniel Madzia has reclassified a nearly complete plesiosaur skeleton found in 1978 in Holzmaden, Germany, as a new genus and species. Named Plesionectes longicollum, this Early Jurassic marine reptile had an extraordinarily long neck and unique skeletal features that challenge previous ideas about plesiosaur evolution during the Toarcian stage, about 183 million years ago.

Hidden for Decades, Misidentified at First

The fossil, known as SMNS 51945, was discovered in the Posidonia Shale, a site famous for exquisitely preserved marine life. After its excavation, it was moved to the Staatliches Museum für Naturkunde Stuttgart, catalogued, and assumed to belong to a known species. For nearly 50 years, it sat in storage without thorough study.

When Sachs and Madzia revisited the specimen, they noticed traits no other Lower Jurassic plesiosaur combined in this way. These included a neck with at least 43 cervical vertebrae—making up 1.25 meters of its estimated 3.2-meter length—V-shaped neurocentral sutures in the vertebrae, and relatively low neural spines.

Even though the skull was heavily damaged, certain bones, like the paraoccipital process and squamosal, offered key diagnostic clues. The researchers concluded it warranted both a new genus and species designation.

Anatomy That Breaks the Mold

The study found Plesionectes longicollum was not only elongated in the neck but also preserved rare traces of soft tissue, allowing for a more complete anatomical picture. The skeleton had four pectoral vertebrae, 20–21 dorsal vertebrae, and a tail made up of 39 vertebrae. Limb bones and girdles suggested an unusual swimming style, possibly linked to ecological specialization.

Its cervical ribs showed both anterior and posterior processes, and in the final neck vertebrae, the rib facets shifted from two co-joined points to a single facet—a configuration seen in only a few other early plesiosaur species.

The relatively small neural spines, compared to other contemporaries, add to its distinction. Importantly, the researchers note these traits are stable and not simply due to the animal’s juvenile age at death.

Life in a Time of Ocean Crisis

This marine reptile lived during the Toarcian Oceanic Anoxic Event, a period of intense climate change marked by higher CO₂ levels, ocean warming, and reduced oxygen in deep waters. These conditions triggered widespread marine extinctions, yet Plesionectes longicollum thrived in this environment. Its presence in early deposits of the Posidonia Shale makes it the oldest known plesiosaur from Holzmaden, predating five other documented species from the site.

The discovery adds evidence that some plesiosaurs adapted quickly to environmental stress, evolving specialized traits that helped them persist while other marine reptiles disappeared. This adaptability points to a more complex evolutionary pattern in Early Jurassic seas than previously thought.

With this addition, Holzmaden’s Posidonia Shale now boasts six known plesiosaur species, further cementing its status as one of the richest fossil sites for marine reptiles of the Lower Jurassic. The find also underscores the untapped scientific value of museum collections. As Sachs and Madzia’s work shows, specimens stored for decades can still transform our understanding of prehistoric life—provided someone looks closely enough.