Plesiopterys

''Plesiopterys'' (“plesio” meaning “near,” and “pterys” meaning “wing” or “pterygoid bone”) is an extinct genus of plesiosaur originating from the Posidonienschiefer of Holzmaden, Germany, and lived during the Early Jurassic period. The type and only species is ''P. wildi'', known from two immature specimens with the subadult measuring long. It possesses a unique combination of both primitive and derived characters, and is currently displayed at the State Museum of Natural History and the Hauff Museum, Germany.

Discovery and naming

In 2004, Frank Robin O'Keefe named the species ''Plesiopterys wildi''. The generic name is a combination of Greek ''plesios'', "near", and ''pterys'', "wing", the latter also referring to the pterygoid bones (apart from the fins). The specific name honors the German paleontologist Rupert Wild for his contributions to the Mesozoic vertebrate paleobiology in Germany.

''P. wildi'' is only known from two complete immature specimens: the juvenile holotype and the referred subadult specimen. The holotype (SMNS 16812) is an almost complete juvenile skeleton found and prepared in the nineteenth century. It is mounted in the Staatliches Museum für Naturkunde, Stuttgart, with the damaged skull replaced by a reconstruction. In 2025, a subadult plesiosaur specimen (MH 7) from the Lower Jurassic Posidonia Shale (Germany) was referred to ''P. wildi''.

In 2007, Fransiska Großmann considered ''Plesiopterys'' a junior synonym of ''Seeleyosaurus guilelmiimperatoris''. Sachs et al. (2025) has since interpreted ''Plesiopterys wildi'' as a taxon distinct from ''S. guilelmiimperatoris''. Marx et al. (2025) also argued that both taxa are separate and that ''Plesiopterys'' is valid based on the shared autapomorphies (derived traits) found in SMNS 16812 and MH 7.

Description

''Plesiopterys wildi'' is a relatively small plesiosaur, with the subadult measuring long. It had a relatively small head and body, and its limbs and limb girdles are similar in proportion to other plesiosaurs. ''Plesiopterys'' had 39 cervical vertebrae, with the neck having general morphology and proportions more similar to ''Thalassiodracon'' than to ''Plesiosaurus''. ''Plesiopterys'' also has 23 dorsal vertebrae, 3 sacral vertebrae and 41 caudal vertebrae. The holotype had specialized grooves on the dorsal side of the pterygoid for attachment of the internal carotid artery, a feature that is not observed in ''Plesiosaurus''.

The holotype was initially thought to be a young adult due to the visible sutures between the centra and neural arch on the cervical vertebrae and based on the interpretation of the other skeletal elements being ossified. However, the cervical neural spines display a shark fin-shape, a feature also known in the osteologically immature holotype of ''Brancasaurus'', which indicates that the holotype of ''Plesiopterys'' is a juvenile.

The subadult specimen MH 7 preserves traces of scaly skin on the right front flipper and smooth skin on the tail, with the tail integument also showing preservation of dark-colored melanosomes and keratinocytes. This specimen suggests that plesiosaurs retained reptilian scaly skin unlike some Mesozoic marine reptiles like ichthyosaurs and metriorhynchids. The scales might have aided the plesiosaurs during swimming or protected the flippers during feeding on the seafloor.

Skull

The skull of specimen SMNS 16812, while well preserved, has a rather crushed skull, with multiple skeletal elements having been broken off, rotated, or otherwise obliterated. On the premaxilla, four or five alveoli are present, along with five premaxillary teeth, which is a plesiomorphic feature for plesiosaurs. Its skull is intermediary between the more primitive ''Thalassiodracon'' and the more derived ''Plesiosaurus''.

The pterygoids are unique in that they possess grooves on the dorsal surface, and extend within the posterior interpterygoid vacuities and the pterygoid covering of the ventral surface of the basisphenoid. There has been some debate regarding the interpretations of the location of the suture between the vomer and the pterygoid, but it is most likely located at the anterior end of the anterior interpterygoid vacuity. This anterior interpterygoid vacuity is rather large, and is bigger than those in ''Thalassiodracon'', ''Rhomaleosaurus'', and '' Leptocleidus''. The large anterior interpterygoid vacuity is not a general autapomorphy. The pterygoid possess thin flanges and extend within the posterior interpterygoid vacuities, and the pterygoid covering of the ventral surface of the basisphenoid. Furthermore, there is no visible suture between the flanges and the quadrate rami of the pterygoids. Dorsally, the thin pterygoid surface displays paired grooves that are oriented posterolateral to anteromedial. This feature is unlike those seen in any known plesiosaur, and is similar to the closed palate on nothosaurs. The cultriform process of the parasphenoid divides the pterygoids, extending towards the posterior end of the anterior interpterygoid vacuity, and is rather narrow. Unlike other early plesiosaurs, there is no evidence of a structure for articulation for a quadrate, but that may be due to degradation.

The mandible retains a prominent mandibular ridge, unlike the rest of plesiosaurids, which have lost the feature. Akin to ''Plesiosaurus'', ''Plesiopterys'' has a simple and unreinforced lower jaw symphysis. Unfortunately, the rest of the mandibular elements of SMNS 16812 are too crushed to identify, so no further significant features could be identified.

The braincase of SMNS 16812 is similarly obstructed, being dislocated from the rest of the skull. However, the exoccipital/opisthotics, basioccipital, and the supraoccipital elements are similar to that seen in ''Thalassiodracon''.

Classification

''Plesiopterys wildi'' is a member of the clade Plesiosauroidea. Phylogenetic analyses have recovered ''Plesiopterys'' as a sister taxon of the genus ''Franconiasaurus'' and the clade Cryptoclidia, in a more derived position than the family Microcleididae.

Paleoenvironment

Specimens of ''Plesiopterys'' are discovered from the Lower Jurassic (Toarcian) Posidonia Shale of Germany. This area is well known for fossil finds of sauropterygians, and is divided into four main zones: Suebian-Franconian, Yorkshire, Luxembourgian, and Norman. The zonation of the area can be used to interpret the distribution of plesiosaurs from the Early Jurassic, as each species is sorted into their respective zones.

The Posidonienshifer, also known as the Posidonia Shale, has yielded a great number of specimens, most abundantly ichthyosaurs and plesiosaurians. ''Plesiopterys wildi'' is accompanied by a few other taxa found in the Holzmaden area, including ''M. brachypterygius'' and ''Hauffiosaurus''.

See also

* List of plesiosaur genera
* Timeline of plesiosaur research

References

{{Taxonbar, from=Q7204675

Jurassic plesiosaurs
Fossils of Germany
Cryptoclididae
Early Jurassic plesiosaurs of Europe
Fossil taxa described in 2004
Sauropterygian genera
Plesiosaurs
Posidonia Shale