Snakes

The snakes (Serpentes) or ophidians (Ophidia) are a suborder of sauropsids (reptiles) diapsids belonging to the order Squamata, of the superorder Lepidosauria, characterized by the absence of legs (the python maintains tiny vestigial limbs, an inheritance from its evolutionary past) and a very elongated body. They originated in the Cretaceous period.

Some perform venomous bites, such as cobras (Elapidae) and vipers, to kill their prey and later ingest it. Other snakes, such as boas and pythons, kill their prey by constriction.

More than 450 genera and 3,460 species are recognized. Snakes are thought to be derived from some type of lizard, but the precise details of their origin are unclear.

Evolution

Among the fossils of basal limbed snakes, we can find the genus Najash.

Anatomy and Physiology

Anatomy of a snake.
1 esophagus, 2 Bring it in. 3 Tracheal lungs, 4 rudimentary left lung, 5 right lung, 6 heart, 7 liver, 8 stomach, 9 Airbag, 10 gallbladder, 11 pancreas, 12 spleen, 13 intestine 14 testicles, 15 kidneys.

Displacement

The anatomy of snakes is specially adapted to be able to move without limbs. Compared with quadrupedal vertebrates, snakes have a very low center of gravity, close to the ground, and a greater body surface area in contact with the ground, which generates greater friction and distributes the body mass more. Despite this, they are capable of swimming, diving, climbing, jumping, digging, and some species can even glide. It presents different types of terrestrial locomotion, the most common form is carried out by means of lateral undulations of the body, which begin at the head and end at the tail. Another type of displacement involves the use of one part of the body as a static anchor to propel the rest of the body. Some snakes can also move in a straight line using their ventral muscles and scales to propel themselves. In addition, some species, especially from desert ecosystems, such as the horned rattlesnake (Crotalus cerastes), move by raising their heads and moving the anterior part of the body forwards, to later raise the middle part of the body and move it, this movement always has two parts of the body in contact with the substratum and one in the air. The widened ventral scales of many snakes prevent sliding in the opposite direction of walking.

Skeleton

The skeleton has many vertebrae, more than 100 in general and in some species reaching more than 400, which makes them very flexible. The variation in the number of vertebrae is related to the length of the snake, but also to its ecology. For example, constrictor species have a greater number of vertebrae than those that use other strategies.

The skull is highly modified from the basic diapsid model. The bones of the upper jaw are loosely attached to the rest of the skull, and the quadrate is free to move and possesses powerful refractive muscles, allowing the jaws to be gaping open and large prey swallowed whole. The teeth are sharp and curved backwards and are implanted both on the palate and on the maxilla and dental.

Boas and pythons have rudiments of their hind limbs and waists; in these snakes claws can be seen on the outside and on each side of the cloaca which play a certain part in coitus.

Senses

Detail view is limited, but does not prevent motion detection. Some snakes have loreal pits, capable of detecting heat. However, this does not indicate that they have infrared vision, since the information goes to areas of the brain other than those of vision. They just know if everything is hotter or colder.

Snakes' sense of hearing is very limited as their hearing organs have degenerated; the eardrum, tympanic cavity, and eustachian tube are missing, and the columella articulates with the quadrate. So it seems unlikely that snakes can clearly hear airborne sounds, but they are certainly sensitive to vibrations in the ground, transmitted through the jaw bones.

A snake smells through its nose; the tongue passes the air particles to the Jacobson's organ in the mouth for examination. Another characteristic of its tongue is that it ends in two branches, which is why it is called forked (the forked tongue is used to capture chemical particles and perceive them with the Jacobson's organ, which is in the front part of the palate).

Skin

Piece of snake skin

Snake skin is covered with scales. Most snakes use scales on the ventral part to move, clinging to surfaces with them. Its eyelids are permanently closed, but are actually transparent scales. Snakes periodically change their skin.

Unlike other reptiles, the change of skin is done in one piece, as if it were pulling on a stocking. This is done as the animal grows and also to repair wounds and get rid of external parasites.

Denture

Solnoglyphs of the snake of Gabon (Bitis gabonica), the largest among all snakes.

There are several types of teeth, depending on the bone on which they are implanted: maxillary, pterygoid, palatine, dental and premaxillary. The maxillary teeth are the most varied and the only ones that can be associated with poisonous glands; Four main types can be distinguished:

• Aglifos.

They are massive, prehensile teeth, curved backwards to hold the prey and are not designed to inoculate venom. This is the case of many colubrids, boids and pythonids. In general, they are harmless snakes for humans, with the exception of the large constrictors (pythons, anacondas).

• Opistoglifos.

They are grooved teeth located in the posterior part of the jaw and connected with venom glands, constituting a primitive inoculation system. Since they must bite with the back of their mouths to inject the venom, they are normally not very dangerous to humans. This is the case of the bastard snake (Malpolon monspessulanus). However, large species can cause severe bites and even death, such as Dispholidus typus, from sub-Saharan Africa.

• Proteroglyphs.

They are small, fixed teeth located at the front of the mouth, with a more or less closed canal. Cobras and mambas have these teeth. Some species, such as the spitting cobra (Naja nigricollis), have them modified to spit venom more than four meters away.

• Solenoglifos.

These are two long mobile fangs in the front part of the jaw; they are hollow with an inner channel closed and connected with venom glands. The fangs fold over the upper palate when the animal closes its mouth and quickly straighten when it opens. It is the most effective inoculation system. This type of dentition is characteristic of viperids.

Internal Organs

Red arrows: infrared receptor organs; black arrows: nasal holes. Up, a python; down, a rattlesnake

The respiratory system and viscera are highly modified since the snake's tubular body requires that all organs be elongated and thin, especially the lungs, kidneys, liver, heart, and testicles. The glottis may project forward to keep the respiratory passage open during prey ingestion, and in some species a part of the trachea is specialized for respiration, forming a tracheal lung.

The left lung is often reduced or sometimes even absent, and the other paired viscera are often at different levels on each side. They have a pair of reproductive organs, called hemipenes in males.

Poison

Extraction of poison from a kind of cobra for obtaining antiophysical serum.

Many species use venom to immobilize or kill their prey. The venom is a modified saliva and is injected through the fangs. The more specialized fangs (viperids) are very long and hollow, and act like real hypodermic needles that stick deep and inject the venom. Other types of fangs, less specialized, have a simple groove on their posterior margin through which the venom descends (cobras).

Snake venom is often specific to its prey, and its role as a defensive mechanism is secondary. The poison, like all salivary secretions, has agents that perform a predigestion of food; therefore, even "non-venomous" can cause tissue damage.

Venom is made up of a complex mixture of proteins that act as neurotoxins (which attack the nervous system), hemotoxins (which damage the blood), cytotoxins (which damage tissues), bungarotoxins, and many other substances that can affect the body. in different ways; almost all snake venoms contain hyaluronidase, an enzyme that destroys hyaluronic acid, which is the cement that holds connective tissue together, which therefore breaks down, thus facilitating the rapid diffusion of venom.

Venom is stored in venom glands on the back of the head. In all venomous snakes, these glands have ducts that open into grooves or canals in the teeth of the upper jaw. Australia is the place in the world with the largest number of poisonous species; however, there is only one death by bite per year on average. In contrast, in India, there are 250,000 bites per year that cause about 50,000 deaths. In Spain, 1,500 snake bites occur each year, of which between three and five cause the death of the victim.

Behavior

Playback

Hemipene in Crotalus atrox.

Most snakes reproduce by laying eggs, but some species have evolved a different method. The mother's body retains the eggs until the young are fully formed to live independently. In this phase, known as the gestation process, complete embryonic development occurs inside the snake.

In some cases the entire group gives birth to fully formed young, while other groups may consist of both members giving birth to fully formed young and members that lay eggs. For example, within the Boidae family, all boas give birth to fully-formed animals, while pythons lay eggs.

Food

Bastard snakeMalpolon monspessulanus) devouring an Iberian lizard (Podarcis hispanica).

All snakes are carnivorous, feeding on a wide variety of prey including birds, amphibians, mammals, fish or invertebrates and even reptiles, including other snakes in certain species. Generally, small to moderate-sized snakes hunt defenseless prey, which can be quickly eaten alive. However, if the prey resists, they may resort to techniques such as the use of poison or constriction to bring down the prey before eating it. Snakes cannot chew their food, and instead swallow it whole. A snake's teeth, which are needle-sharp and directed into the mouth, serve to retain prey from slipping out of its mouth. When swallowing, the maxilla and mandible, which are attached to the skull by ligaments, manage to separate to accommodate the size of the prey. Thus, a snake is capable of swallowing a prey that is three times larger than its own head and its diameter. Another reason for its ability to swallow is the lack of bones such as the sternum so that food can pass smoothly down the esophagus and throughout the reptile's body. After ingestion, a snake must go to sleep to complete the digestion process. This is because the digestive process requires a lot of energy that the snake must use to efficiently digest the food, which can last days or months, depending on the size of the prey. In this state, some organs such as the heart and the stomach become more active so that all the food is almost totally digested. The indigestible parts can be excreted or regurgitated.

Diversity

Snakes have almost as wide an adaptive radiation as lizards, although the structural variation is not as great.

Emerald Boa (Corallus batesii).

Boas and pythons

The families of boidae and pythonidae include the most primitive species of snakes, as evidenced by the fact that they still retain rudiments of hind legs. They lack venom and kill their prey by constriction, coiling around it until they suffocate. They include today's largest snakes, such as the anaconda and reticulated python. Pythons typically measure between 1 and 6 m, although some species are among the longest extant snakes; the reticulated python holds the record for the longest snake, at 10.32 m.

Staircase snake (Rhinechis scalaris).

Snakes

Most living snakes belong to the colubrid family, which includes many harmless, medium-sized species such as the European water snake (Natrix maura), the southern smooth snake (Coronella girondica) or the ladder snake (Rhinechis scalaris), and some moderately poisonous, with opisthoglyphous teeth (located at the back of the mouth), such as the bastard snake (Malpolon monspessulanus); the Cape tree snake (Dispholidus) is one of the few species whose bite can be fatal to humans.

Cover of glasses (Naja naja).

Cobras, mambas and corals

The elapid family includes cobras, coral snakes, mambas, and sea snakes, all of which are extremely venomous and potentially deadly to humans; the fangs are small and located in the front part of the mouth (proteroglyphs); its venom has a mainly neurotoxic action. All Australian venomous snakes belong to this group. Terrestrial elapids are similar to colubrids; almost all have long, slender bodies, heads covered with large scales and not always distinct from the neck, and eyes with round pupils. Furthermore, their behavior is generally quite active, and many species are oviparous. Mambas (Dendroaspis) are arboreal and are very agile and fast. Coral snakes have their bright warning colors since they are very poisonous (aposematism), among which yellow, red and black predominate; They are not very dangerous for humans since they are small and open their mouths a little, which makes it difficult for them to bite. Cobras (Naja, Ophiophagus and Hemachatus) are well known for their menacing appearance and bite; they inhabit tropical and desert areas of southern Asia and Africa; they display a kind of "hood" in the head and neck area when they are irritated or in danger, thanks to the long cervical ribs; it is a warning gesture before a possible enemy.

Schlegel's horny petal (Bothriechis schlegelii).

Snakes and Rattlesnakes

The viperid family includes Old World vipers and rattlesnakes, mainly American; all of them are very venomous and with two solenoglyphous fangs provided with a channel that act as hypodermic needles when they bite to inject venom. The venom has a mainly hemolytic action. The fangs are very long and fold against the roof of the mouth when the mouth is closed, unfolding rapidly when the snake is about to attack its prey. The head is triangular and wide, and the eyes have a vertical pupil. Most retain the eggs that contain the young inside the body, giving birth to the young after hatching from the inside of the body, that is, they are ovoviviparous.

Among its species are the European vipers (Vipera), the most venomous animals on the continent, the African horned vipers (Cerastes), the asp, the Gabon (Bitis, with the longest fangs of all snakes), American rattlesnakes (Crotalus, Lachesis), etc.

Taxonomy

All snakes belong to the clade Serpentes, which in turn is a member of the order Squamata. This order also includes the lizards, with which snakes are related; other members of this order, the blind shingles, have also lost their legs and superficially resemble snakes.

Snakes include Henophidia (the largest and most primitive, boas and pythons), Typhlopoidea (blind snakes), and Xenophidia (a highly diverse group that includes venomous snakes and their close relatives (snakes, vipers, cobras, snakes, etc.) marinas, etc.).^{[citation required]}

The suborder Snakes is subdivided into two infraorders and 25 families:

• Infraorden Alethinophidia
  • Family Acrochordidae
  • Aniliidae
  • Anomochilidae
  • Family Atractaspididae
  • Family Boidae
  • Family Bolyeriidae
  • Family Colubridae
  • Cylindrophiidae family
  • Elapidae family
  • Homalopsidae
  • Lamprophiidae
  • Loxocemidae
  • Family Pareatidae
  • Pythonidae
  • Family Tropidophiidae
  • Uropeltidae family
  • Family Viperidae
  • Xenodermatidae
  • Xenopeltidae
  • Xenophiidae
• Infraorden Scolecophidia
  • Anomalepididae
  • Family Gerrhopilidae
  • Family Leptotyphlopidae
  • Family Typhlopidae
  • Xenotyphlopidae family

Phylogeny

Recent molecular studies corroborate the monophyly of the Serpentes clade and the infraorders Scolecophidia and Alethinophidia.

Beliefs

Lilith with a snake (John Collier, 1892).

Sculpture of the bronze serpent of the Rod of Moses (in the form of caducee) on Mount Nebo in Jordan.

Snakes have been appreciated in various cultures, but disowned in others.

In the West, in Christian beliefs and Islam, the devil has been represented with snakes, in this case with Satan according to the Bible, where he recounts his sentence for tempting Adam and Eve. Even in the first chapters and verses of Genesis, after committing the temptation, she recounts how God, apart from telling her that she will crawl and walk on her chest, there will also be enmity between her and the woman who will bite her heel and the woman will bite her. will break your head.

This biblical story has inspired the Catholic Church to represent the Virgin Mary as the Immaculate Conception stepping on a snake as recounted in Genesis, but instead of biting the heel the reptile only carries an apple in its mouth. In some cases, Jesus Christ has also been represented stepping on a snake, but not inspired by the genesis of the Bible but as a representation of the fight between good and evil, which this symbology can also be applied to the case of the Virgin Mary.

Within Christianity there are also other opinions that can be considered contradictory, some theologians based on the story of Moses in the biblical story, to free the Hebrew people, God turned his staff into a snake in the middle of the burning bush when Moses came in contact. According to this story, it is interpreted that God through Moses demonstrated his fury against the Egyptian people in front of Pharaoh. In this, some theologians consider that the staff of Moses, known as the rod of Moses, is a serpent with a positive or at the same time miraculous aspect.

In Ancient Egypt, Wadjet (the cobra) was the "Lady of Heaven", a symbol of the burning heat of the Sun and the flame of fire. She represented the force of growth, the fertility of the soil and of the waters in Egyptian mythology. She was the protective goddess of Lower Egypt and of the pharaoh. However, the serpent Apophis was the symbol of the evil forces that inhabit the Duat, and tried to retain the solar boat of Ra.

In the Ancient Near East, the serpent was considered a long-lived, beneficent and healing animal, hence the emblem of the caduceus.

In the Far East, the snake is considered a sacred, divine animal and protector against negative energies, representing strength, energy and wisdom. It is also revered mainly within the Hindi culture. For example in Christianity, the Holy Spirit is represented as a white dove, but here, God Siva is represented as a snake, on a cobra.

Chinese culture also considers it a protective entity; An example of this is found in the Great Wall of China built on a mountainous terrain and located in the center of yellow. It has also been represented alongside the Dragon as a symbol of some oriental martial arts. In this animal, the different methods of self defense in ancient China have been inspired, mainly created and rescued by teachers or Shifus or martial artists. Also within Chinese astrology, the Sign of the Serpent, occupies the 6th place and as the successor part of the Sign of the Dragon, according to Chinese philosophy it is also part of the Ying yang.

Similarly, in America they have been revered by a large part of the cultures that flourished there. In Mesoamerica, the most famous example is that of the god Quetzalcóatl, the Feathered Serpent, Kukulcán for the Mayas. In South America there is the mythical figure of the Amaru or winged serpent, a very ancient deity and of great importance in the worldview of the Quechua and Aimara peoples. In the Mapuche people, two powerful beings in the form of mythical snakes called Trentren Vilu and Caicai Vilu are described; Caicai-Vilu being a "sea serpent" who has the power to dominate the sea and everything related to it, and Trentren-Vilu an "terrestrial serpent" who has power to dominate the earth, and its volcanoes.

In ancient Rome, the god Aesculapius (god of medicine) took the form of a serpent, which has given its name to the serpent of Aesculapius. In this case the snakes were also revered.

The basilisk is represented in some cultures as a large serpent with a crown-shaped spot on its head that, if it is direct, is capable of killing and, if it is indirect, it petrifies.