A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.
A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.
The skull of a snake is a very complex structure, with numerous joints to allow the snake to swallow prey far larger than its head.
The typical snake skull has a solidly ossified braincase, with the separate frontal bones and the united parietal bones extending downward to the basisphenoid, which is large and extends forward into a rostrum extending to the ethmoidal region. The nose is less ossified, and the paired nasal bones are often attached only at their base. The occipital condyle is either trilobate and formed by the basioccipital and the exoccipitals, or a simple knob formed by the basioccipital; the supraoccipital is excluded from the foramen magnum. The basioccipital may bear a curved ventral process or hypapophysis in the vipers.
The prefrontal bone is situated, on each side, between the frontal bone and the maxilla, and may or may not be in contact with the nasal bone.
The postfrontal bone, usually present, borders the orbit behind, rarely also above, and in the pythons a supraorbital bone is intercalated between it and the prefrontal bone.
The premaxillary bone is single and small and as a rule, connected with the maxillary only by ligament.
The paired vomer is narrow.
The palatine bone and pterygoid are long and parallel to the axis of the skull, the latter diverging behind and extending to the quadrate or to the articular extremity of the mandible; the pterygoid is connected with the maxillary by the ectopterygoid or transverse bone, which may be very long, and the maxillary often emits a process towards the palatine, the latter bone being usually produced inwards and upwards towards the anterior extremity of the basisphenoid.
The quadrate is usually large and elongate, and attached to the cranium through the supratemporal (often regarded as the squamosal).
In rare cases, ( Polemon ) the transverse bone is forked and articulates with the two branches of the maxilla.
The quadrate and maxillary and palatopterygoid arches are more or less movable to allow for the distension required by the passage of prey, often much exceeding the size of the mouth. For the same reason, the rami of the lower jaw, which consist of dentary, splenial, angular, and articular elements, with the addition of a coronoid in the boas and a few other small families, are connected at the symphysis by a very extensible elastic ligament.
The hyoid apparatus is reduced to a pair of cartilaginous filaments situated below the trachea, and united in front.
There are various modifications according to the genera. A large hole may be present between the frontal bones and the basisphenoid ( Psammophis , Coelopeltis ); the maxillary may be much abbreviated and movable vertically, as in the Viperidae; the pterygoids may taper and converge posteriorly, without any connection with the quadrate, as in the Amblycephalidae; the supratemporal may be much reduced, and wedged in between the adjacent bones of the cranium; the quadrate may be short or extremely large; the prefrontals may join in a median suture in front of the frontals; the dentary may be freely movable, and detached from the articular posteriorly.
The deviation from the normal type is much greater still when we consider the degraded wormlike members of the families Typhlopidae and Glauconiidae, in which the skull is very compact and the maxillary much reduced. In the former this bone is loosely attached to the lower aspect of the cranium; in the latter, it borders the mouth and is suturally joined to the premaxillary and the prefrontal. Both the transverse bone and the supratemporal are absent, but the coronoid element is present in the mandible.
In most snakes, teeth are located on the dentary of the lower jaw, the maxilla, the palatine bone and the lateral pterygoid plate. The latter form an "inner row" of teeth that can move separately from the rest of the jaws and are used to help "walk" the jaws over prey. Several snake lineages have evolved venom which is typically delivered by specialized teeth called fangs located on the maxilla.
Most snakes can be placed into one of four groups, based on their teeth, which correlate strongly with venom and lineage.
Aglyphous snakes (lacking grooves) have no specialized teeth; each tooth is similar in shape and often size. When teeth vary in size, as in some bird eaters, they do not vary in shape. Most aglyphous snakes are non-venomous; some, like Thamnophis , are considered mildly venomous. The feature is not a synapomorphy.
Opisthoglyphous ("rearward grooves") snakes possess venom injected by a pair of enlarged teeth at the back of the maxillae, which normally angle backward and are grooved to channel venom into the puncture. Since these fangs are not located at the front of the mouth, this arrangement is vernacularly called "rear-fanged". In order to envenomate prey, an opisthoglyphous snake must move the prey into the rear of its mouth and then penetrate it with its fangs, presenting difficulties with large prey although they can quickly move smaller prey into position. The opisthoglyphous dentition appears at least two times in the history of snakes. [1] The venom of some opisthoglyphous snakes is strong enough to harm humans; notably, herpetologists Karl Schmidt and Robert Mertens were killed by a boomslang and a twig snake, respectively, [2] [3] after each underestimated the effects of the bite and failed to seek medical help. Opisthoglyphous snakes are found mostly in the families Colubridae and Homalopsidae.
Proteroglyphous snakes (forward grooved) have shortened maxillae bearing few teeth except for a substantially enlarged fang pointing downwards and completely folded around the venom channel, forming a hollow needle. Because the fangs are only a fraction of an inch long in even the largest species, these snakes must hang on, at least momentarily, as they inject their venom. [4] Some spitting cobras have modified fang tips allowing them to spray venom at an attacker's eyes. This form of dentition is unique to elapids.
Solenoglyphous snakes (pipe grooved) have the most advanced venom delivery method of any snake. Each maxilla is reduced to a nub supporting a single hollow fang tooth. The fangs, which can be as long as half the length of the head, are folded against the roof of the mouth, pointing posteriorly. The skull has a series of interacting elements that ensure that the fangs rotate into biting position when the jaws open. Solenoglyphous snakes open their mouths almost 180 degrees, and the fangs swing into a position to allow them to penetrate deep into the prey. While solenoglyph venom is typically less toxic than that of proteroglyphs, this system allows them to deeply inject large quantities of venom. This form of dentition is unique to vipers.
A few snakes do not conform to these categories. Atractaspis is solenoglyphous but the fangs swing out sideways, allowing it to strike without opening its mouth, perhaps allowing it to hunt in small tunnels. Scolecophidia (blind burrowing snakes) typically have few teeth, often only in the upper or lower jaw.
Common names for the various types of snake dentition originate largely from older literature, but still are encountered in informal publications. Aglyphous snakes are commonly called fangless; opisthoglyphous snakes rear-fanged or back-fanged; and both Proteroglyphous and Solenoglyphous snakes are referred to as front-fanged. [5] [6]
Modifications of the skull in the European genera:
A snake has from 175 to more than 400 vertebrae in its backbone. The means by which vertebrae are secured are twofold: either a ball and socket joint, or zygopophyses, which stick out from each vertebra to poke rear-pointing projections from the vertebrae ahead of it. This results in a spine well-adapted to the snake's method of movement. [7]
The vertebral column consists of an atlas (composed of two vertebrae) without ribs; numerous precaudal vertebrae, all of which, except the first or first three, bear long, movable, curved ribs with a small posterior tubercle at the base, the last of these ribs sometimes forked; two to ten so-called lumbar vertebrae without ribs, but with bifurcate transverse processes (lymphapophyses) enclosing the lymphatic vessels; and a number of ribless caudal vertebrae with simple transverse processes. When bifid, the ribs or transverse processes have the branches regularly superposed.
The centra have the usual ball and socket joint, with the nearly hemispherical or transversely elliptic condyle at the back (procoelous vertebrae), while the neural arch is provided with additional articular surfaces in the form of pre- and post-zygapophyses, broad, flattened, and overlapping, and of a pair of anterior wedge-shaped processes called zygosphene, fitting into a pair of corresponding concavities, zygantrum, just below the base of the neural spine. Thus the vertebrae of snakes articulate with each other by eight joints in addition to the cup-and-ball on the centrum, and interlock by parts reciprocally receiving and entering one another, like the mortise and tenon joints. The precaudal vertebrae have a more or less high neural spine which, as a rare exception (Xenopholis), may be expanded and plate-like above, and short or moderately long transverse processes to which the ribs are attached by a single facet. The centra of the anterior vertebrae emit more or less developed descending processes, or haemapophyses, which are sometimes continued throughout, as in Tropidonotus , Vipera , and Ancistrodon , among European genera.
In the caudal region, elongate transverse processes take the place of ribs, and the haemapophyses are paired, one on each side of the haemal canal. In the rattlesnakes the seven or eight last vertebrae are enlarged and fused into one.
No living snake shows any remains of the pectoral arch, but remains of the pelvis are found in:
In vertebrates, the maxilla is the upper fixed 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. The two maxillary bones are fused at the intermaxillary suture, forming the anterior nasal spine. This is similar to the mandible, which is also a fusion of two mandibular bones at the mandibular symphysis. The mandible is the movable part of the jaw.
Lesothosaurus is a monospecific genus of ornithischian dinosaur that lived during the Early Jurassic in what is now South Africa and Lesotho. It was named by paleontologist Peter Galton in 1978, the name meaning "lizard from Lesotho". The genus has only one valid species, Lesothosaurus diagnosticus. Lesothosaurus is one of the most completely-known early ornithischians, based on numerous skull and postcranial fossils from the Upper Elliot Formation. It had a simpler tooth and jaw anatomy than later ornithischians, and may have been omnivorous in some parts of the year.
In anatomy, a process is a projection or outgrowth of tissue from a larger body. For instance, in a vertebra, a process may serve for muscle attachment and leverage, or to fit, with another vertebra. The word is also used at the microanatomic level, where cells can have processes such as cilia or pedicels. Depending on the tissue, processes may also be called by other terms, such as apophysis, tubercle, or protuberance.
Macroplata is an extinct genus of Early Jurassic rhomaleosaurid plesiosaur which grew up to 4.65 metres (15.3 ft) in length. Like other plesiosaurs, Macroplata probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward stroke for fast swimming. Macroplata also had a relatively long neck, twice the length of the skull, in contrast to pliosaurs. It is known from a nearly complete skeleton NHMUK PV R5488 from the Blue Lias Formation (Hettangian) of Harbury, Warwickshire, UK.
Elginia is an extinct genus of pareiasaurid known from the Late Permian of Scotland and China. It was named for the area around Elgin in Scotland, which has yielded many fossils referred to as the Elgin Reptiles.
Askeptosaurus is an extinct genus of askeptosauroid, a marine reptile from the extinct order Thalattosauria. Askeptosaurus is known from several well-preserved fossils found in Middle Triassic marine strata in what is now Italy and Switzerland.
Jiangjunosaurus is a genus of herbivorous stegosaurian dinosaur from the Oxfordian-age Shishugou Formation of the Junggar Basin, Xinjiang, China.
Anatosuchus is an extinct genus of notosuchian crocodyliforms discovered in Gadoufaoua, Niger, and described by a team of palaeontologists led by the American Paul Sereno in 2003, in the Journal of Vertebrate Paleontology. Its duck-like snout coincidentally makes it resemble a crocoduck, an imagined hybrid animal with the head of a crocodile and the body of a duck.
Goronyosaurus is an extinct genus of marine lizard belonging to the mosasaur family. Fossils of Goronyosaurus are exclusively known from the Late Maastrichtian of the Iullemmeden Basin in West Africa, specifically the Dukamaje Formation of Niger and Nigeria and Farin Doutchi Formation of Niger. The type specimen was first described in 1930 as Mosasaurus nigeriensis, but subsequent remains revealed a highly unique set of adaptations that prompted the species to be reclassified as the only species of the new genus Goronyosaurus in 1972. These unique adaptations have made Goronyosaurus notoriously difficult to classify within the Mosasauridae and it is often left out of phylogenetic analyses, although most authors agree that Goronyosaurus belonged to Mosasauridae.
Adamantinasuchus is an extinct genus of notosuchian crocodylomorph from and named after the Late Cretaceous Adamantina Formation of Brazil. It is known from only one fossil, holotype UFRJ-DG 107-R, collected by William Nava. The fossil consists of a partial skull, fragmentary limb bones and a few broken vertebrae, and was found 25 kilometres (16 mi) southwest of the town of Marilia, near a reservoir dam. Adamantinasuchus was approximately 60 centimetres (24 in) long from nose to tail, and would have only weighed a few kilograms.
Plesiotylosaurus, meaning "near Tylosaurus", is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like Mosasaurus and Prognathodon. The genus contains one species, Plesiotylosaurus crassidens, recovered from deposits of Middle Maastrichtian age in the Moreno Formation in California.
Vancleavea is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is V. campi, named by Robert Long & Phillip A Murry in 1995. At that time, the genus was only known from fragmentary bones including osteoderms and vertebrae. However, since then many more fossils have been found, including a pair of nearly complete skeletons discovered in 2002. These finds have shown that members of the genus were bizarre semiaquatic reptiles. Vancleavea individuals had short snouts with large, fang-like teeth, and long bodies with small limbs. They were completely covered with bony plates known as osteoderms, which came in several different varieties distributed around the body. Phylogenetic analyses by professional paleontologists have shown that Vancleavea was an archosauriform, part of the lineage of reptiles that would lead to archosaurs such as dinosaurs and crocodilians. Vancleavea lacks certain traits which are present in most other archosauriforms, most notably the antorbital, mandibular and supratemporal fenestrae, which are weight-saving holes in the skulls of other taxa. However, other features clearly support its archosauriform identity, including a lack of intercentra, the presence of osteoderms, an ossified laterosphenoid, and several adaptations of the femur and ankle bones. In 2016, a new genus of archosauriform, Litorosuchus, was described. This genus resembled both Vancleavea and more typical archosauriforms in different respects, allowing Litorosuchus to act as a transitional fossil linking Vancleavea to less aberrant archosauriforms.
Australothyris is an extinct genus of basal procolophonomorph parareptile known from the Middle Permian of Tapinocephalus Assemblage Zone, South Africa. The type and only known species is Australothyris smithi. As the most basal member of Procolophonomorpha, Australothyris helped to contextualize the origin of this major parareptile subgroup. It has been used to support the hypotheses that procolophonomorphs originated in Gondwana and ancestrally possess temporal fenestrae, due to its large and fully enclosed temporal fenestra and South African heritage. It also possessed several unique features, including a high tooth number, long postfrontal, small interpterygoid vacuity, and a specialized interaction between the stapes and quadrate.
Fodonyx is an extinct genus of rhynchosaur from the middle Triassic epoch of Devon in England. Its fossils were discovered in Otter Sandstone Formation and were first assigned to Rhynchosaurus spenceri. This species was reassigned to its own genus, Fodonyx the holotype of which is EXEMS 60/1985/292, that described by David W. E. Hone and Michael J. Benton in 2008. In 2010, one skull was reassigned to the new genus Bentonyx. It is distinguished from other rhynchosaurs by a single autapomorphy, the ventral angling of the paraoccipital processes. In all other rhynchosaurs these processes angle dorsally or are horizontal. It is not known if this conferred any advantage to Fodonyx. Fodonyx was between 40 and 50 cm long.
Daemonosaurus is an extinct genus of possible theropod dinosaur from the Late Triassic of New Mexico. The only known fossil is a skull and neck fragments from deposits of the latest Triassic Chinle Formation at Ghost Ranch. Daemonosaurus was an unusual dinosaur with a short skull and large, fang-like teeth. It lived alongside early neotheropods such as Coelophysis, which would have been among the most common dinosaurs by the end of the Triassic. However, Daemonosaurus retains several plesiomorphic ("primitive") traits of the snout, and it likely lies outside the clade Neotheropoda. It may be considered a late-surviving basal theropod or non-theropod basal saurischian, possibly allied to other early predatory dinosaurs such as herrerasaurids or Tawa.
Jesairosaurus is an extinct genus of early archosauromorph reptile known from the Illizi Province of Algeria. It is known from a single species, Jesairosaurus lehmani. Although a potential relative of the long-necked tanystropheids, this lightly-built reptile could instead be characterized by its relatively short neck as well as various skull features.
Palatodonta is an extinct genus of neodiapsid reptile known from the early Middle Triassic of the Netherlands. It was initially described in 2013 as a basal placodontiform closely related to a group of marine reptiles called placodonts, characterized by their crushing teeth and shell-like body armor. Under this interpretation, Palatodonta is transitional between placodonts and less specialized reptiles. Like placodonts, it has a row of large teeth on its palate, but while these teeth are thick and blunt in placodonts, Palatodonta has palatal teeth that are thin and pointed. A 2023 study instead classified it as a sauropterygomorph and the sister taxon to Eusaurosphargis. In other words, it is close to, but not within, Sauropterygia.
This glossary explains technical terms commonly employed in the description of dinosaur body fossils. Besides dinosaur-specific terms, it covers terms with wider usage, when these are of central importance in the study of dinosaurs or when their discussion in the context of dinosaurs is beneficial. The glossary does not cover ichnological and bone histological terms, nor does it cover measurements.
Rugarhynchos is an extinct genus of doswelliid archosauriform from the Late Triassic of New Mexico. The only known species is Rugarhynchos sixmilensis. It was originally described as a species of Doswellia in 2012, before receiving its own genus in 2020. Rugarhynchos was a close relative of Doswellia and shared several features with it, such as the absence of an infratemporal fenestra and heavily textured skull bones. However, it could also be distinguished by many unique characteristics, such as a thick diagonal ridge on the side of the snout, blunt spikes on its osteoderms, and a complex suture between the quadratojugal, squamosal, and jugal. Non-metric multidimensional scaling and tooth morphology suggest that Rugarhynchos had a general skull anatomy convergent with some crocodyliforms, spinosaurids, and phytosaurs. However, its snout was somewhat less elongated than those other reptiles.
Eurycephalosuchus is an extinct genus of orientalosuchine alligatoroid from the Late Cretaceous Jiangxi Province of China. Known from a well preserved skull and mandible alongside various postcranial remains, Eurycephalosuchus possessed a short and broad skull with a very short skulltable. Eurycephalosuchus lived with at least one other crocodilian, an indetermined member of the clade Brevirostres. The genus is monotypic, containing only the species Eurycephalosuchus gannanensis.