Vadasaurus is an extinct genus of rhynchocephalian closely related to the aquatic pleurosaurids. Although this genus was not as specialized as the eel-like pleurosaurs for aquatic life, various skeletal features support the idea that it had a semiaquatic lifestyle. The type species, Vadasaurus herzogi, was described and named in 2017. It was discovered in the Solnhofen Limestone in Germany, which is dated to the Late Jurassic. The generic name "Vadasaurus" is derived from "vadare", which is Latin for "to go" or "to walk forth", and "saurus", which means "lizard" (although rhynchocephalians are not lizards). "Vadare" is the root of the English word "wade", which is the reason it was chosen for this genus, in reference to its perceived semiaquatic habits. The specific name, "herzogi", refers to Werner Herzog, a Bavarian filmmaker.
Description
The holotype of Vadasaurus herzogi is AMNH FARB 32768, a well-preserved but slightly flattened skeleton which is practically complete.
Skull and teeth
The part of the skull in front of the eyes is rather short, but the rear part is long, with elongated temporal fenestrae (holes in the back of the skull). As a whole the skull is triangular in shape. The lower temporal fenestrae, on the sides of the skull, are very large, about a quarter the length of the entire skull. The premaxillae are not fused together, and each possess a large fang seemingly formed from three fused teeth. The front part of the premaxilla is very short, but the rear part is long, excluding the maxilla from the long nares (nostril holes). Each maxilla possesses about thirteen or fourteen acrodont teeth which are fused to the bone (as is typical for rhynchocephalians). The first six or seven teeth are tiny and simple. However, the latter seven are much larger and more complex. These teeth increase in size towards the back of the skull and possess a pointed cusp followed by a low ridge.
The nasal bones on the top of the snout are thin and separate from each other at the back of the snout to make room for the triangular front edge of the frontals. The bones of the skull roof (frontals and parietals) are not fused to their respective pairs, and the parietals form a sagittal crest between the upper temporal fenestrae on the top of the skull. The parietal foramen (a hole which holds the "third eye" in modern tuataras) is teardrop-shaped. The postorbital, jugal, and squamosal bones on the side of the head curve upwards to form the bar between the upper and lower temporal fenestrae. The jugal lacks a "subtemporal extension" forming the bottom edge of the lower temporal fenestra, leaving the hole open from the bottom as if it was an arch. The squamosal also forms a large portion of the part of the skull behind the lower temporal fenestra, along with a thin and tall quadratojugal and a curved quadrate which probably supported a tympanic membrane (eardrum).
The bones of the roof of the mouth are mostly obscured, but were partially revealed by a micro-CT scan of the specimen. Each of the palatines possess a row of teeth, although the form of such teeth cannot be determined. The palatines themselves are separated by the long and thin front parts of the pterygoids, which do not seem to possess teeth.
The lower jaw is more shallow than those of other advanced sphenodontians, but not as much as that of Pleurosaurus. It is smoothly curved, with the front tip at a higher level than the lower edge. The front part of the jaw is toothless, but the rear part has a row of teeth. Each tooth possesses a cusp preceded by a long ridge and followed by a short ridge. The outer edge of the teeth have been partially worn away by contact with the maxillary teeth.
Spine, tail, and ribs
The specimen preserves seven cervical (neck) vertebrae, sixteen dorsal (back) vertebrae, two sacral (hip) vertebrae, and forty-two caudal (tail) vertebrae. This gives Vadasaurus a very long tail. The neural spines on the top of the vertebrae (particularly the cervicals) are short and rectangular. The pre- and post-zygapophyses on the side of the vertebrae are swollen, making the vertebrae hourglass-shaped from above. Each rib is thinnest in the middle. A jumble of thin bones in the middle part of the body are probably the remains of gastralia (belly ribs) and components of a cartilaginous sternum. The sacral vertebrae are partially fused to each other. Most of the caudal vertebrae possess tapering ribs which are flattened from the side. The last few caudal vertebrae are thin and very simple.