From the depths of Germany’s legendary Posidonia Shale, scientists have unveiled a new marine reptile species: Plesionectes longicollum, meaning “long-necked near-swimmer.” This elegant plesiosauroid once glided through Jurassic seas nearly 183 million years ago, and its almost complete skeleton, soft tissues, and all were dug up back in 1978 in Holzmaden.
After decades on the museum shelf, a fresh scientific deep dive revealed that this fossil wasn’t just another plesiosaur; it was something entirely new. With a unique mix of skeletal traits, it earned its own genus and species name.
Back in 1978, a nearly complete plesiosaur skeleton was unearthed from a quarry in Holzmaden, Germany. It was impressive, even preserving traces of soft tissue, but for decades, scientists only scratched the surface.
Earlier studies were brief, focusing on isolated features like its skin, while its complete anatomy and identity remained a mystery.
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In this study, paleontologists finally gave this fossil the spotlight it deserved. Through a detailed reexamination, they uncovered a unique blend of skeletal traits that didn’t match any known plesiosaur. These features weren’t just quirks of a young specimen; they were distinct enough to declare a new genus and species: Plesionectes longicollum, the “long-necked near-swimmer.
The fossil-rich Posidonia Shale in Holzmaden, Germany, has long been a treasure trove of prehistoric marine life. But a new study reveals it’s even richer than we thought. Paleontologists have identified Plesionectes longicollum as the oldest known plesiosaur from the region.
Credit
Plesionectes skeleton at the Staatliches Museum für Naturkunde Stuttgart
Although the specimen was immature, its bones told a mature story. The team found a distinct mix of skeletal traits that weren’t just juvenile quirks; they were unique enough to justify a brand-new genus and species. This means the fossil, cataloged as SMNS 51945, adds a whole new branch to the plesiosaur family tree.
Plesionectes longicollum is a newly identified plesiosaur that stands out due to a distinctive combination of anatomical features. It had an exceptionally long neck made up of at least 43 vertebrae, measuring 125 cm, with wide, strap-shaped rib bones in the front and middle sections.
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The back of its skull featured a long bony extension, longer than the height of the bone it connected to. Its neck and chest vertebrae showed a V-shaped joint pattern, and most of the neck bones had fused rib attachment points, forming a single facet.
The spines along its back were relatively short and lacked narrowing at the base, and it had 20 to 21 vertebrae in its back region. The preserved skeleton measures 295 cm, but with the skull included, the full length of the animal is estimated at 320 cm, roughly 10.5 feet long.
Co-author Dr. Daniel Madzia from the Polish Academy of Sciences said, “This discovery adds another piece to the puzzle of marine ecosystem evolution during a critical time in Earth’s history. The early Toarcian period, when this animal lived, was marked by significant environmental changes, including a major oceanic anoxic event that affected marine life worldwide.”
The fossil is permanently housed at the Staatliches Museum für Naturkunde Stuttgart (Stuttgart State Museum of Natural History).
Journal Reference
- Sachs S, Madzia D. 2025. An unusual early-diverging plesiosauroid from the Lower Jurassic Posidonia Shale of Holzmaden, Germany. PeerJ 13:e19665 DOI: 10.7717/peerj.19665