This is a collection of lists of

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

gestation period estimated by experts in their fields. The mammals included are only

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

(

marsupials Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a ...

and

placentals Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...

) as some mammals, which are

monotremes Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified ...

(including

platypuses The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

and

echidnas Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae , living in Australia and New Guinea. The four extant species of echidnas and the platypus are the only l ...

) lay their

eggs An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

. A marsupial has a short gestation period, typically shorter than placental. For more information on how these estimates were ascertained, see Wikipedia's articles on

gestational age In obstetrics, gestational age is a measure of the age of a pregnancy taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method, if available. Such metho ...

. The gestation figures given here are shown in days. They represent average values and should only be considered as approximations.

Factors affecting the gestation period in mammals

There are several factors affecting the length of the gestation period in mammals.

Animal size/mass

There is a positive relationship between mass at birth and length of gestation in eutherian mammals. Larger mammals are more likely to produce a well-developed neonate than small mammals. Large mammals develop at an absolute slower rate compared to small mammals. Thus, the large mammal tend have longer gestation periods than small mammal as they tend to produce larger neonate. Large mammals require a longer period of time to attain any proportion of adult mass compared to small mammals.

The level of development at birth

More developed infants will typically require a longer gestation period.

Altricial Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. Altricial ...

mammals needs less time to gestate compare to the

precocial Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. Altricial ...

(well-developed neonate) mammal. A typical precocial mammal has a gestation period almost four times longer than a typical altricial mammal of the same body size. Precocial mammal species generally have greater adult body weights than altricial mammals as precocial mammals have markedly longer gestation periods than altricial mammals. The neonatal of larger mammals develop relatively more quickly and thus making it more likely that a large mammal would produce a more well-developed neonate as a consequence of its longer gestation period. In some cases, some mammal species may have similar gestation periods despite having significantly different body masses.

Environmental factor

In response to the conditions of the environment, some mammals, such as

bat Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...

delay the implantation due to the cold temperature in winter. Another factor is due to the shortage of food stocks during winter as the insects are being driven away and as the result, bat hibernate in pregnant condition. In

pinnipeds Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the walr ...

, the purpose of delayed implantation is in order to increase survival chance of the young animals as the mother ensure that the neonates are born at an optimal season. Scheffer, V. B., & York, A. E. (1997). Timing of implantation in the northern fur seal, Callorhinus ursinus. Journal of Mammalogy, 78(2), 675-683.

References

Citations

Sources

Gestation, Incubation, and Longevity of Selected Animals
*

David Crystal David Crystal, (born 6 July 1941) is a British linguist who works on the linguistics of the English language. Crystal studied English at University College London and has lectured at Bangor University and the University of Reading. He was aw ...

, ''

The Cambridge Factfinder ''The'' is a grammatical article in English, denoting nouns that are already or about to be mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The' ...

'' Cambridge:

Cambridge University Press Cambridge University Press was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessme ...

, 1998 (84).
Online animal encyclopedia

Study finds wide range in pregnancy length
* {{DEFAULTSORT:Gestation Period Fertility Midwifery