New Species of Jurassic Marine Reptile Discovered in Germany

In August 2025, paleontologists Sven Sachs and Dr. Daniel Madzia unveiled a new species of Jurassic marine reptile, Plesionectes longicollum, in the journal PeerJ. This discovery stems from a nearly complete skeleton excavated in 1978 from the Posidonia Shale in Holzmaden, Germany.

The specimen, cataloged as SMNS 51945, had been housed at the Staatliches Museum für Naturkunde Stuttgart since its discovery. Through comprehensive analysis, Sachs and Madzia identified unique anatomical features distinguishing it from known plesiosaurs, leading to the classification of a new genus and species. The name Plesionectes combines the Greek words "plēsíon" (near) and "nēktēs" (swimmer), while "longicollum" derives from the Latin words "longus" (long) and "collum" (neck), referencing the species' elongated neck.

"This specimen has been in collections for decades, but previous studies never fully explored its distinctive anatomy," said Sven Sachs. "Our detailed examination revealed an unusual combination of skeletal features that clearly distinguish it from all previously known plesiosaurs."

The Posidonia Shale, also known as the Sachrang Formation, is an Early Jurassic geological formation renowned for its exceptionally preserved fossils. Located in southwestern Germany, including the Holzmaden area, this formation dates back to the early Toarcian stage, approximately 183 million years ago. The shale's unique depositional environment has yielded a diverse array of marine fossils, including ichthyosaurs, plesiosaurs, ammonites, and crinoids. Holzmaden, a small town with fewer than 800 inhabitants, is particularly famous for its wealth of superbly preserved fossils, making it a significant site for paleontological research.

The specimen SMNS 51945 is a remarkably well-preserved, nearly complete skeleton of a plesiosauroid plesiosaur. Despite being an immature individual, its distinctive anatomical characteristics were not significantly affected by its developmental stage, warranting classification as an entirely new genus and species. The fossil even preserves remnants of fossilized soft tissue, providing rare insights into the physiology of these ancient marine reptiles. This discovery adds another piece to the puzzle of marine ecosystem evolution during a critical time in Earth's history, marked by significant environmental changes, including a major oceanic anoxic event that affected marine life worldwide.

The identification of Plesionectes longicollum underscores the rich biodiversity of the Early Jurassic marine ecosystems and highlights the importance of re-examining existing fossil collections. This discovery not only adds to the known plesiosaur diversity of both the Toarcian age and the Posidonia Shale but also provides valuable insights into the evolutionary history of marine reptiles. The presence of a unique suite of osteological characters found in SMNS 51945 justifies the erection of a new genus and species, contributing to our understanding of the morphological diversity and evolutionary pathways of plesiosaurs.

"This discovery adds another piece to the puzzle of marine ecosystem evolution during a critical time in Earth's history," explained Dr. Madzia.

The Posidonia Shale has been a focus of scientific interest for the last 100 years. The first fossils were recorded in 1598 by the medical doctor Johannes Bauhin, who interpreted the local ammonites as "metallic things" in rocks and as "miraculous tricks" of nature, while the crinoids were interpreted as either huge flowers or heads of medusa, and evidence of the biblical flood. Many people did important geological and paleontological research on the Swabian Posidonia Shale, including Carl Hartwig von Zieten (1785–1846), Eberhard Fraas (1862–1915), Bernhard Hauff senior (1866–1950), and Adolf Seilacher (1925–2014).

The first geological studies were carried out, motivated by the extraction of shales in the southern quarries. Several fossils were reported, studied, and named at the time from locations such as Banz Abbey, Ohmden, Holzmaden, or Dotternhausen, including Macrospondylus in 1824 (as Steneosaurus, being originally identified as a Gharial), the pterosaur Dorygnathus (as a species of Pterodactylus) in 1830, the fish Lepidotes, the selachian Hybodus, or the crinoid Pentacrinites.