Vadasaurus
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''Vadasaurus'' is an extinct
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of rhynchocephalian closely related to the aquatic pleurosaurids. Although this genus was not as specialized as the
eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
-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 Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, which is dated to the Late
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
. The generic name "''Vadasaurus"'' is derived from "''vadare''", which is
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
for "to go" or "to walk forth", and "''saurus''", which means " lizard" (although rhynchocephalians are not lizards). "''Vadare"'' is the root of the
English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...
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 Werner Herzog (; born 5 September 1942) is a German film director, screenwriter, author, actor, and opera director, regarded as a pioneer of New German Cinema. His films often feature ambitious protagonists with impossible dreams, people with u ...
, a
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n
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.


Description

The
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
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
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
e 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 The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
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 A cusp is the most pointed end of a curve. It often refers to cusp (anatomy), a pointed structure on a tooth. Cusp or CUSP may also refer to: Mathematics * Cusp (singularity), a singular point of a curve * Cusp catastrophe, a branch of bifurc ...
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 The third eye (also called the mind's eye or inner eye) is a mystical invisible eye, usually depicted as located on the forehead, which provides perception beyond ordinary sight. In Hinduism, the third eye refers to the ajna (or brow) chakra. In ...
" in modern
tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...
s) is teardrop-shaped. The
postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ...
,
jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
, and
squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...
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 The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...
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 X-ray microtomography, like tomography and X-ray computed tomography, uses X-rays to create cross-sections of a physical object that can be used to recreate a virtual model (3D model) without destroying the original object. The prefix ''micro-'' ...
scan of the specimen. Each of the
palatines Palatines (german: Pfälzer), also known as the Palatine Dutch, are the people and princes of Palatinates ( Holy Roman principalities) of the Holy Roman Empire. The Palatine diaspora includes the Pennsylvania Dutch and New York Dutch. In 1709 ...
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)
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
e, 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 Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In thes ...
(belly ribs) and components of a
cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...
. 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.


Limbs and pelvis

The humerus is short but proportionally similar to that of other rhynchocephalians when compared to the body length of the animal. The hand possesses five fingers, with the longest being finger IV, followed by fingers III, II, V, and I. The phalangeal formula of the hand (which describes the number of bones in each finger starting with finger I) is ?-3-4-5-3. Each finger ends in a curved claw. The
metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...
(hand bone) corresponding to finger I is characteristically wide. The ilium is short and tapers towards the rear. The top edge of the pubis is large and rounded while the back edge is arched, creating a large thyroid fenestra between the pubis and ischium. The ischium is larger than the pubis and has a bony spur which could have connected to tail muscles. The
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...
is S-shaped but the finer details of its structure (as well as the structure of the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
and
fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity i ...
) are poorly developed. The astragalus and calcaneum (ankle bones) are unfused. Metatarsal I (the first foot bone) is short and wide while metatarsals II-IV are much longer. Metatarsal V is even shorter and wider, with a hooked outer edge. The phalangeal formula of the foot is 2-3-4-5-4, and each toe is long and ends in a curved claw, similar to those of the hand.


Classification

''Vadasaurus herzogi'' is believed to be a close relative of the pleurosaurids according to a
phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
published in its description. The clade comprising this genus and Pleurosauridae is itself allied with '' Kallimodon'' and '' Sapheosaurus''. Although the structure of Rhynchocephalia as a whole is changeable depending on the methodology used in the analysis, the ''Vadasaurus'' + Pleurosauridae clade seems to be one of most well-supported parts of the whole order. The discovery of ''Vadasaurus'' helps to depict the evolution of the pleurosaurids. Although not technically a true pleurosaurid, ''Vadasaurus'' still possesses several features characteristic of the family, such as a long tail and nares, a wide metacarpal and metatarsal I, and limbs which are less well-ossified than those of other rhynchocephalians.


Paleobiology

''Vadasaurus'' is believed to have been at least partially aquatic, perhaps similar in lifestyle to the Galapagos marine iguana, ''Amblyrhynchus cristatus''. It possessed thicker and heavier ribs and gastralia which may have functioned as ballast. Although a large amount of skeletal evidence provides evidence for the idea that the holotype specimen of ''Vadasaurus'' died in adulthood, the
epiphyses The epiphysis () is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the jo ...
of its forelimb bones were not completely fused. This is further evidence for a semiaquatic lifestyle, as animals which spend a large portion of their time in the water do not experience the forces of terrestrial locomotion to the same extent as fully terrestrial animals. Although the limb bones of terrestrial animals strengthen during development, semiaquatic animals have less need for such strengthening, and as a lineage becomes more inclined to an aquatic lifestyle, the limbs become less inclined to fully ossify as they develop. ''Vadasaurus's'' not-fully-fused forelimbs are an intermediate form between the strong limbs of terrestrial rhynchocephalians and the weaker limbs of pleurosaurids.


References

{{Taxonbar, from=Q48247552 Sphenodontia Late Jurassic reptiles of Europe Solnhofen fauna Fossil taxa described in 2017