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Birth is the act or process of bearing or bringing forth
offspring
In biology, offspring are the young creation of living organisms, produced either by a single organism or, in the case of sexual reproduction, two organisms. Collective offspring may be known as a brood or progeny in a more general way. This ca ...
, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the
uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
to contract, expelling the fetus at a developmental stage when it is ready to feed and breathe.
In some species the offspring is
precocial
In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
and can move around almost immediately after birth but in others it is
altricial
In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
and completely dependent on parenting.
In
marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
s, the fetus is born at a very immature stage after a short
gestation
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...
and develops further in its mother's womb
pouch.
It is not only mammals that give birth. Some reptiles, amphibians, fish and invertebrates carry their developing young inside them. Some of these are
ovoviviparous
Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...
, with the eggs being hatched inside the mother's body, and others are
viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
, with the
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
developing inside her body, as in the case of mammals.
Mammals
Large
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, such as
primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
s,
cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...
,
horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...
s, some
antelope
The term antelope is used to refer to many species of even-toed ruminant that are indigenous to various regions in Africa and Eurasia.
Antelope comprise a wastebasket taxon defined as any of numerous Old World grazing and browsing hoofed mammals ...
s,
giraffe
The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, ''Giraffa camelopardalis ...
s,
hippopotamus
The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...
es,
rhinoceros
A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species o ...
es,
elephant
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
s,
seals
Seals may refer to:
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impress an emblem, used as a means of a ...
,
whale
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
s,
dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
s, and
porpoise
Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...
s, generally are pregnant with one offspring at a time, although they may have twin or multiple births on occasion.
In these large animals, the birth process is similar to that of a human, though in most the offspring is
precocial
In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
. This means that it is born in a more advanced state than a human baby and is able to stand, walk and run (or swim in the case of an aquatic mammal) shortly after birth.
[
In the case of whales, dolphins and porpoises, the single calf is normally born tail first which minimizes the risk of drowning. The mother encourages the newborn calf to rise to the surface of the water to breathe.
Most smaller mammals have multiple births, producing litters of young which may number twelve or more. In these animals, each fetus is surrounded by its own amniotic sac and has a separate placenta. This separates from the wall of the uterus during labor and the fetus works its way towards the birth canal.
Large mammals which give birth to twins is much more rare, but it does occur occasionally even for mammals as large as elephants. In April 2018, approximately 8-month old elephant twins were sighted joining their mother's herd in the Tarangire National Park of Tanzania, estimated to have been born in August 2017.
]
Human childbirth
Humans usually produce a single offspring at a time. The mother's body is prepared for birth by hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
s produced by the pituitary gland
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...
, the ovary
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
and the placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
. The total gestation period
In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once it ...
from fertilization
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
to birth is normally about 38 weeks (birth usually occurring 40 weeks after the last menstrual period
The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible. The ovarian cycle controls the production and release of eggs ...
). The normal process of childbirth takes several hours and has three stages. The first stage starts with a series of involuntary contractions of the muscular walls of the uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
and gradual dilation of the cervix. The active phase of the first stage starts when the cervix is dilated more than about 4 cm in diameter and is when the contractions become stronger and regular. The head (or the buttocks in a breech birth
A breech birth is when a baby is born bottom first instead of head first, as is normal. Around 3–5% of pregnant women at term (37–40 weeks pregnant) have a breech baby. Due to their higher than average rate of possible complications for the ...
) of the baby is pushed against the cervix
The cervix or cervix uteri (Latin, 'neck of the uterus') is the lower part of the uterus (womb) in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during ...
, which gradually dilates until is fully dilated at 10 cm diameter. At some time, the amniotic sac
The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shor ...
bursts and the amniotic fluid
The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...
escapes (also known as rupture of membranes Rupture of membranes (ROM) or amniorrhexis is a term used during pregnancy to describe a rupture of the amniotic sac. Normally, it occurs spontaneously at full term either during or at the beginning of labor. Rupture of the membranes is known col ...
or breaking the water). In stage two, starting when the cervix is fully dilated, strong contractions of the uterus and active pushing by the mother expels the baby out through the vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
, which during this stage of labour is called a birth canal as this passage contains a baby, and the baby is born with umbilical cord
In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologic ...
attached. In stage three, which begins after the birth of the baby, further contractions expel the placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
, amniotic sac, and the remaining portion of the umbilical cord usually within a few minutes.
Enormous changes take place in the newborn's circulation to enable breathing
Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.
All aerobic creatures need oxygen for cellular ...
in air. In the uterus, the fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
is dependent on circulation of blood through the placenta for sustenance including gaseous exchange and the unborn baby's blood bypasses the lungs by flowing through the foramen ovale, which is a hole in the septum dividing the right atrium
The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two at ...
and left atrium
The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two atr ...
. After birth the umbilical cord is clamped and cut, the baby starts to breathe air, and blood from the right ventricle
A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper ...
starts to flow to the lungs for gaseous exchange and oxygenated blood returns to the left atrium
The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two atr ...
, which is pumped into the left ventricle
A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper ...
, and then pumped into the main arterial system. As a result of these changes, the blood pressure in the left atrium exceeds the pressure in the right atrium, and this pressure difference forces the foramen ovale to close separating the left and right sides of the heart. The umbilical vein
The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood v ...
, umbilical arteries
The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord.
Structure Development
The umbilical arteries supply deoxygenated bl ...
, ductus venosus
In the fetus, the ''ductus venosus'' (Arantius' duct after Julius Caesar Aranzi) shunts a portion of umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. Compared to ...
and ductus arteriosus
The ''ductus arteriosus'', also called the ''ductus Botalli'', named after the Italian physiologist Leonardo Botallo, is a blood vessel in the developing fetus connecting the trunk of the pulmonary artery to the proximal descending aorta. It a ...
are not needed for life in air and in time these vessels become ligaments (embryonic remnants).
Cattle
Birthing in cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...
is typical of a larger mammal. A cow
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
goes through three stages of labor during normal delivery of a calf. During stage one, the animal seeks a quiet place away from the rest of the herd. Hormone changes cause soft tissues of the birth canal to relax as the mother's body prepares for birth. The contractions of the uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
are not obvious externally, but the cow may be restless. She may appear agitated, alternating between standing and lying down, with her tail slightly raised and her back arched. The fetus is pushed toward the birth canal by each contraction and the cow's cervix
The cervix or cervix uteri (Latin, 'neck of the uterus') is the lower part of the uterus (womb) in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during ...
gradually begins to dilate. Stage one may last several hours, and ends when the cervix is fully dilated. Stage two can be seen to be underway when there is external protrusion of the amniotic sac
The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shor ...
through the vulva, closely followed by the appearance of the calf's front hooves and head in a front presentation (or occasionally the calf's tail and rear end in a posterior presentation).[ During the second stage, the cow will usually lie down on her side to push and the calf progresses through the birth canal. The complete delivery of the calf (or calves in a multiple birth) signifies the end of stage two. The cow scrambles to her feet (if lying down at this stage), turns round and starts vigorously licking the calf. The calf takes its first few breaths and within minutes is struggling to rise to its feet. The third and final stage of labor is the delivery of the ]placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
, which is usually expelled within a few hours and is often eaten by the normally herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
cow.
Dogs
Birth is termed whelping in dogs. Among dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s, as whelping approaches, contractions become more frequent. Labour in the bitch can be divided into 3 stages. The first stage is when the cervix dilates, causing discomfort and restlessness in the bitch. Common signs of this stage are panting, fasting, and/or vomiting. This may last up to 12 hours. Stage two is the passage of the offspring. The amniotic sac
The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo (and later fetus) until shor ...
looking like a glistening grey balloon, with a puppy inside, is propelled through the vulva
The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external sex organ, female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, bulb of vestibu ...
. After further contractions, the sac is expelled and the bitch breaks the membranes, releasing clear fluid and exposing the puppy. The mother chews at the umbilical cord and licks the puppy vigorously, which stimulates it to breathe. If the puppy has not taken its first breath within about six minutes, it is likely to die. Further puppies follow in a similar way one by one usually with less straining than the first usually at 15-60-minute intervals. If a pup has not been passed in 2 hours a veterinarian should be contacted. Stage three is the passing of the placentas. This often occurs in conjunction with stage two with the passing of each offspring. The mother will then usually eat the afterbirth. This is an adaption to keep the den clean and prevent its detection by predators.
Marsupials
An infant marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
is born in a very immature state. The gestation period is usually shorter than the intervals between oestrus periods. The first sign that a birth is imminent is the mother cleaning out her pouch. When it is born, the infant is pink, blind, furless and a few centimetres long. It has nostrils in order to breathe and forelegs to cling onto its mother's hairs but its hind legs are undeveloped. It crawls through its mother's fur and makes its way into the pouch. Here it fixes onto a teat which swells inside its mouth. It stays attached to the teat for several months until it is sufficiently developed to emerge. Joeys are born with "oral shields"; in species without pouches or with rudimentary pouches these are more developed than in forms with well-developed pouches, implying a role in maintaining the young attached to the mother's nipple.
Other animals
Many reptiles and the vast majority of invertebrates, most fish, amphibians and all birds are oviparous
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...
, that is, they lay eggs with little or no embryonic development taking place within the mother. In aquatic organisms, fertilization is nearly always external with sperm and eggs being liberated into the water (an exception is sharks and rays, which have internal fertilization). Millions of eggs may be produced with no further parental involvement, in the expectation that a small number may survive to become mature individuals. Terrestrial invertebrates may also produce large numbers of eggs, a few of which may avoid predation and carry on the species. Some fish, reptiles, and amphibians have adopted a different strategy and invest their effort in producing a small number of young at a more advanced stage which are more likely to survive to adulthood. Birds care for their young in the nest and provide for their needs after hatching and it is perhaps unsurprising that internal development does not occur in birds, given their need to fly.
Ovoviviparity
Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...
is a mode of reproduction in which embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
s develop inside egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s that remain in the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
species in that there is internal fertilization
Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For inter ...
and the young are born in an advanced state, but differ in that there is no placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
l connection and the unborn young are nourished by egg yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...
. The mother's body provides gas exchange
Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...
(respiration), but that is largely necessary for oviparous animals as well.[ In many ]shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...
s the eggs hatch in the oviduct within the mother's body and the embryos are nourished by the egg's yolk and fluids secreted by glands in the walls of the oviduct. The Lamniforme
The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the grea ...
sharks practice ''oophagy
Oophagy ( ) sometimes ovophagy, literally "egg eating", is the practice of
embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek (, "egg") and classical Greek (, ...
'', where the first embryos to hatch consume the remaining eggs and sand tiger shark
The sand tiger shark (''Carcharias taurus''), gray nurse shark, spotted ragged-tooth shark or blue-nurse sand tiger, is a species of shark that inhabits subtropical and temperate waters worldwide. It inhabits the continental shelf, from sandy sho ...
pups cannibal
Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, bo ...
istically consume neighbouring embryos. The requiem sharks maintain a ''placental'' link to the developing young, this practice is known as viviparity
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
. This is more analogous to mammalian gestation than to that of other fishes. In all these cases, the young are born alive and fully functional. The majority of caecilian
Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics of ...
s are ovoviviparous and give birth to already developed offspring. When the young have finished their yolk sacs they feed on nutrients secreted by cells lining the oviduct
The oviduct in mammals, is the passageway from an ovary. In human females this is more usually known as the Fallopian tube or uterine tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, o ...
and even the cells themselves which they eat with specialist scraping teeth. The Alpine salamander
The alpine salamander (''Salamandra atra'') is a black salamander that can be found in the French Alps, and through the mountainous range in Europe. It is a member of the genus ''salamandra''. Their species name, ''atra'', may be derived from the ...
(''Salamandra atra'') and several species of Tanzanian toad in the genus ''Nectophrynoides
''Nectophrynoides'' is a genus of true toads, family Bufonidae. They are endemic to Eastern Arc forests and wetlands in Tanzania,Channing and Howell. (2006). ''Amphibians of East Africa.'' Pp. 104–117. and all except '' N. tornieri'' are thr ...
'' are ovoviviparous, developing through the larval stage inside the mother's oviduct and eventually emerging as fully formed juveniles.
A more developed form of viviparity
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
called placental viviparity is adopted by some species of scorpion
Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always end ...
s and cockroaches, certain genera of sharks
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...
, snake
Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
s and velvet worm
Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...
s. In these, the developing embryo is nourished by some form of placental structure. The earliest known placenta was found recently in a group of extinct fishes called placoderms
Placodermi (from Greek πλάξ 'plate' and δέρμα 'skin', literally 'plate-skinned') is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their head and thorax were ...
. A fossil from Australia's
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by a ...
Gogo Formation
The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community. The formation is named after Gogo Station, a cattle station where outcrops appear and fossils ...
, laid down in the Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
period, 380 million years ago, was found with an embryo inside it connected by an umbilical cord
In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologic ...
to a yolk sac
The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is far ...
. The find confirmed the hypothesis that a sub-group of placoderms, called ptyctodontids, fertilized their eggs internally. Some fishes that fertilize their eggs internally also give birth to live young, as seen here. This discovery moved our knowledge of live birth back 200 million years. The fossil of another genus was found with three embryos in the same position. Placoderms are a sister group of the ancestor of all living jawed fishes (Gnathostomata
Gnathostomata (; from Greek: (') "jaw" + (') "mouth") are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, living ...
), including both chondrichthyians, the sharks & rays, and Osteichthyes
Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilage ...
, the bony fishes.
Among lizards, the viviparous lizard
The viviparous lizard, or common lizard, (''Zootoca vivipara'', formerly ''Lacerta vivipara''), is a Eurasian lizard. It lives farther north than any other species of non-marine reptile, and is named for the fact that it is viviparous, meaning ...
''Zootoca vivipara'', slow worms and many species of skink
Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Ski ...
are viviparous, giving birth to live young. Some are ovoviviparous but others such as members of the genera '' Tiliqua'' and ''Corucia
The Solomon Islands skink (''Corucia zebrata''), also known as prehensile-tailed skink, monkey-tailed skink, giant skink, zebra skink, and monkey skink, is an arboreal species of skink endemic to the Solomon Islands archipelago. It is the larg ...
'', give birth to live young that develop internally, deriving their nourishment from a mammal-like placenta attached to the inside of the mother's uterus. In a recently described example, an African species, ''Trachylepis ivensi'', has developed a purely reptilian placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
directly comparable in structure and function to a mammalian placenta. Vivipary is rare in snake
Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
s, but boas and viper
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
s are viviparous, giving birth to live young.
The majority of insects lay eggs but a very few give birth to offspring that are miniature versions of the adult.[ The ]aphid
Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...
has a complex life cycle and during the summer months is able to multiply with great rapidity. Its reproduction is typically parthenogenetic
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
and viviparous and females produce unfertilized eggs which they retain within their bodies. The embryos develop within their mothers' ovarioles
An ovariole is a tubular component of the insect ovary, and the basic unit of egg production. Each ovariole is composed of a germarium (the germline stem cell niche) at the anterior tip, a set of developing oocytes contained within follicles, an ...
and the offspring are clones
Clone or Clones or Cloning or Cloned or The Clone may refer to:
Places
* Clones, County Fermanagh
* Clones, County Monaghan, a town in Ireland
Biology
* Clone (B-cell), a lymphocyte clone, the massive presence of which may indicate a pathologi ...
of their mothers. Female nymphs
A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are typ ...
are born which grow rapidly and soon produce more female offspring themselves. In some instances, the newborn nymphs already have developing embryos inside them.[
]
See also
* Animal sexual behaviour
Animal sexual behaviour takes many different forms, including within the same species. Common mating or Reproduction, reproductively motivated systems include Monogamous pairing in animals, monogamy, Polygyny in animals, polygyny, Polyandry ...
* Breeding season
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and cha ...
* Caesarean section
Caesarean section, also known as C-section or caesarean delivery, is the surgical procedure by which one or more babies are delivered through an incision in the mother's abdomen, often performed because vaginal delivery would put the baby or mo ...
* Dystocia
Obstructed labour, also known as labour dystocia, is the baby not exiting the pelvis because it is physically block during childbirth although the uterus contracts normally. Complications for the baby include not getting enough oxygen which may ...
* Episiotomy
Episiotomy, also known as perineotomy, is a surgical incision of the perineum and the posterior vaginal wall generally done by a midwife or obstetrician. Episiotomy is usually performed during second stage of labor to quickly enlarge the opening ...
* Foaling (horses)
* Forceps delivery
Obstetrical forceps are a medical instrument used in childbirth. Their use can serve as an alternative to the ventouse (vacuum extraction) method.
Medical uses
Forceps births, like all assisted births, should only be undertaken to help prom ...
* Kegel exercises
* Mating system
A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to animals, the term describes which males and females mating, mate under which circumstances. Reco ...
* Odon device
* Perineal massage
* Reproduction
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...
* Reproductive system
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
* Ventouse
Vacuum extraction (VE), also known as ventouse, is a method to assist delivery of a baby using a vacuum device. It is used in the second stage of labor if it has not progressed adequately. It may be an alternative to a forceps delivery and cae ...
* Birth spacing
Birth spacing, pregnancy spacing, inter-birth interval (IBI) or inter-pregnancy interval refers to how soon after a prior pregnancy a woman becomes pregnant or gives birth again. There are health risks associated both with pregnancies placed closel ...
References
Cited texts
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Animal developmental biology