List of mammalian gestation durations
This is a collection of lists of mammal gestation period estimated by experts in their fields. The mammals included are only viviparous (marsupials and placentals) as some mammals, which are monotremes (including platypuses and echidnas) lay their eggs. 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.
The gestation figures given here are shown in days. They represent average values and should only be considered as approximations.
Mammal | Gestation period (days)[1] | Reference | ||
---|---|---|---|---|
Min | Max | Average | ||
Aardvark (Orycteropus afer) | 213 | [2] | ||
Anteater (Giant) (Myrmecophaga tridactyla) | 170 | 190 | 180 | [3] |
Ape (Bonobo) (Pan paniscus) | 196 | 260 | 228 | [4] |
Ape (Bornean orangutan) (Pongo pygmaeus) | 234 | [5] | ||
Ape (Chimpanzee) (Pan troglodytes) | 230 | 250 | 240 | [4] |
Ape (Gorilla) (Genus Gorilla) | 255 | 260 | 257 | [4] |
Ape (Human) (Homo sapiens) | 259 | 275 | 270 | [6] |
Ape (Lar gibbon) (Hylobates lar) | 220 | [4] | ||
Ape (Siamang) (Symphalangus syndactylus) | 236 | [4] | ||
Armadillo (Nine-banded) (Dasypus novemcinctus) | 120 | [6] | ||
Armadillo (Six-banded) (Euphractus sexcinctus) | 62 | |||
Badger (American) (Taxidea taxus) | 60 | [6] | ||
Bat (Common vampire) (Desmodus rotundus) | 213 | [7] | ||
Bat (Little brown) (Myotis lucifugus) | 50 | 60 | 55 | [8] |
Bear (Black) (Ursus americanus) | 220 | [9] | ||
Bear (Giant panda) (Ailuropoda melanoleuca) | 95 | 160 | 127 | [10] |
Bear (Grizzly) (Ursus arctos) | 215 | [6] | ||
Bear (Polar) (Ursus maritimus) | 241 | [6] | ||
Bovid (American bison) (Bison bison) | 285 | |||
Bovid (Barbary sheep) (Ammotragus lervia) | 158 | [6] | ||
Bovid (Bay duiker) (Cephalophus dorsalis) | 120 | [6] | ||
Bovid (Bighorn sheep) (Ovis canadensis) | 180 | [5] | ||
Bovid (Blackbuck) (Antilope cervicapra) | 165 | [5] | ||
Bovid (Cattle) (Bos taurus) | 279 | 287 | 283 | [11] |
Bovid (Common eland) (Taurotragus oryx) | 255 | [6] | ||
Bovid (Domestic goat) (Capra hircus) | 145 | 155 | 150 | [6] |
Bovid (Domestic sheep) (Ovis aries) | 150 | [6] | ||
Bovid (Domestic yak) (Bos grunniens) | 255 | [6] | ||
Bovid (Dorcas gazelle) (Gazella dorcas) | 132 | [5] | ||
Bovid (Impala) (Aepyceros melampus) | 191 | [5] | ||
Bovid (Mountain goat) (Oreamnos americanus) | 176 | [5] | ||
Bovid (Sable antelope) (Hippotragus niger) | 270 | [5] | ||
Bovid (Thomson's gazelle) (Gazella thomsonii) | 165 | [5] | ||
Bovid (Zebu) (Bos indicus) | 280 | [6] | ||
Camelid (Alpaca) (Lama pacos) | 345 | [12][13] | ||
Camelid (Bactrian camel) (Camelus bactrianus) | 360 | 420 | 390 | |
Camelid (Llama) (Lama glama) | 330 | [6] | ||
Canid (African wild dog) (Lycaon pictus) | 71 | [5] | ||
Canid (Bat-eared fox) (Otocyon megalotis) | 65 | [6] | ||
Canid (Coyote) (Canis latrans) | 62 | [5] | ||
Canid (Domestic dog) (Canis familiaris) | 58 | 65 | 61 | |
Canid (Golden jackal) (Canis aureus) | 62 | [5] | ||
Canid (Island fox) (Urocyon littoralis) | 63 | [6] | ||
Canid (Red fox) (Vulpes vulpes) | 52 | [5] | ||
Canid (Wolf) (Canis lupus) | 60 | 68 | 64 | |
Cat (Canadian lynx) (Lynx canadensis) | 60 | [6] | ||
Cat (Cheetah) (Acinoyx jubatus) | 92 | [5] | ||
Cat (Domestic) (Felis catus) | 58 | 67 | 64 | |
Cat (Leopard) (Panthera pardus) | 92 | 95 | 93 | [6] |
Cat (Lion) (Panthera leo) | 108 | [6] | ||
Cat (Puma) (Puma concolor) | 90 | |||
Cat (Tiger) (Panthera tigris) | 105 | 113 | 109 | |
Deer (Chital) (Axis axis) | 218 | [6] | ||
Deer (Common fallow) (Dama dama) | 228 | [5] | ||
Deer (Elk, aka Wapiti) (Cervus canadensis) | 240 | 250 | 245 | [6] |
Deer (Moose) (Alces alces) | 240 | 250 | 245 | |
Deer (Mule) (Odocoileus hemionus) | 206 | [5] | ||
Deer (Père David's) (Elaphurus davidianus) | 284 | [6] | ||
Deer (Red) (Cervus elaphus) | 238 | [5] | ||
Deer (Reindeer) (Rangifer tarandus) | 215 | [5] | ||
Deer (Sambar) (Rusa unicolor) | 246 | [6] | ||
Deer (White-tailed) (Odocoileus virginianus) | 201 | |||
Elephant shrew (Bushveld) (Elephantulus intufi) | 51 | [6] | ||
Elephant shrew (Eastern rock) (Elephantulus myurus) | 46 | [6] | ||
Elephant (African bush) (Loxodonta africana) | 670 | [14] | ||
Elephant (African forest) (Loxodonta cyclotis) | 670 | [15] | ||
Elephant (Asian) (Elephas maximus) | 548 | 670 | 609 | [16] |
Equid (Burchell's_zebra) (Equus quagga burchelli) | 390 | [5] | ||
Equid (Donkey) (Equus asinus) | 335 | 426 | 365 | [5] |
Equid (Grant's zebra) (Equus quagga boehmi) | 361 | 390 | 375 | |
Equid (Horse) (Equus caballus) | 330 | 342 | 336 | [6] |
Ferret (Domestic) (Mustela furo) | 41 | 42 | 41 | [17] |
Galago (Family Galagidae) | 124 | [5] | ||
Giraffe (Genus Giraffa) | 420 | 450 | 430 | |
Hare (European) (Lepus europaeus) | 41 | [6] | ||
Hedgehog (European) (Erinaceus europaeus) | 34 | [6] | ||
Hippopotamus (Common) (Hippopotamus amphibius) | 225 | 250 | 237 | [6] |
Hyena (Striped) (Hyaena hyaena) | 90 | [18] | ||
Hyrax (Rock) (Procavia capensis) | 255 | [6] | ||
Kinkajou (Potos flavus) | 77 | [6] | ||
Lemur (Superfamily Lemuroidea) | 128 | [5] | ||
Manatee (West Indian) (Trichechus manatus) | 365 | 426 | 396 | [19] |
Marsupial (Kangaroo) (Family Macropodidae) | 42 | |||
Marsupial (Koala) (Phascolarctos cinereus) | 34 | [20] | ||
Marsupial (Quokka) (Setonix brachyurus) | 26 | [6] | ||
Marsupial (Stripe-faced dunnart) (Sminthopsis macroura) | 9.5 | 12 | 11 | [21] |
Marsupial (Virginia opossum) (Didelphis virginiana) | 12 | 13 | 12 | |
Marsupial (Wombat) (Family Vombatidae) | 26 | 28 | 27 | |
Mink (European) (Mustela lutreola) | 38 | 76 | 57 | [17] |
Monkey (Baboon) (Genus Papio) | 185 | [22] | ||
Monkey (Blue) (Cercopithecus mitis) | 140 | [4] | ||
Monkey (Bonnet macaque) (Macaca radiata) | 153 | 169 | 161 | [4] |
Monkey (Brown woolly) (Lagothrix lagothrica) | 139 | [4] | ||
Monkey (Celebes crested macaque) (Macaca nigra) | 155 | 175 | 164 | [4] |
Monkey (Crab-eating macaque) (Macaca fascicularis) | 153 | 179 | 165 | [4] |
Monkey (Dusky leaf) (Trachypithecus obscurus or Presbytis obscurus) | 150 | [4] | ||
Monkey (Formosan rock macaque) (Macaca cyclopis) | 163 | [4] | ||
Monkey (Gelada) (Theropithecus gelada) | 170 | [4] | ||
Monkey (Goeldi's marmoset) (Callimico goeldii) | 149 | 152 | 151 | [4] |
Monkey (Golden lion tamarin) (Leontopithecus rosalia) | 131 | [5] | ||
Monkey (Gracile capuchin) (Genus Cebus) | 180 | [4] | ||
Monkey (Grey-cheeked mangabey) (Cercocebus albigena) | 174 | [4] | ||
Monkey (Grivet) (Cercopithecus aethiops) | 210 | [4] | ||
Monkey (Guenon) (Genus Cercopithecus) | 160 | [5] | ||
Monkey (Japanese macaque) (Macaca fuscata) | 150 | 180 | 166 | [4] |
Monkey (King colobus) (Colobus polykomos) | 180 | 213 | 202 | [4] |
Monkey (Mantled howler) (Alquatta paliatta) | 139 | [6] | ||
Monkey (Northern plains gray langur) (Semnopithecus entellus or Presbytis entellus) | 183 | [4] | ||
Monkey (Patas) (Erythrocebus patas) | 192 | [4] | ||
Monkey (Proboscis) (Nasalis larvatus) | 166 | [4] | ||
Monkey (Red-shanked douc) (Pygathrix nemaeus) | 180 | 190 | 185 | [4] |
Monkey (Red-tailed) (Cercopithecus ascanius) | 190 | [4] | ||
Monkey (Rhesus macaque) (Macaca mulatta) | 164 | [4] | ||
Monkey (Southern pig-tailed macaque) (Macaca nemestrina) | 168 | 171 | 170 | [4] |
Monkey (Spider) (Genus Ateles) | 139 | [4] | ||
Monkey (Squirrel) (Genus Saimiri) | 167 | [5] | ||
Monkey (Stump-tailed macaque) (Macaca arctoides) | 168 | 184 | 182 | [4] |
Monkey (Talapoin) (Cercopithecus talapoin) | 196 | [4] | ||
Monkey (Tamarin) (Genus Saguinus) | 162 | [5] | ||
Monkey (Toque macaque) (Macaca sinica) | 180 | [4] | ||
Monkey (Vervet) (Cercopithecus pygerythrus) | 195 | [6] | ||
Otter (Subfamily Lutrinae) | 60 | 86 | 73 | |
Pig (Domestic) (Sus domesticus) | 112 | 115 | 113 | |
Pig (Wild boar) (Sus scrofa) | 120 | [6] | ||
Pinniped (California sea lion) (Zalophus californianus) | 350 | [6] | ||
Pinniped (Northern fur seal) (Callorhinus ursinus) | 254 | [6] | ||
Pinniped (Southern elephant seal) (Mirounga leonina) | 335 | [23] | ||
Pinniped (Walrus) (Odobenus rosmarus) | 456 | |||
Pinniped (Weddel seal) (Leptonychotes wedelli) | 310 | [6] | ||
Pronghorn (Antilocapra americana) | 246 | [5] | ||
Rabbit (Domestic) (Oryctolagus cuniculus domesticus) | 28 | 35 | 31 | [17] |
Raccoon (Common) (Procyon lotor) | 63 | [6] | ||
Rhinoceros (Black) (Diceros bicornis) | 450 | |||
Rhinoceros (Indian) (Rhinoceros unicornis) | 478 | [18] | ||
Rhinoceros (White) (Ceratotherium simum) | 467 | [5] | ||
Rodent (Beaver) (Genus Castor) | 122 | |||
Rodent (Chinchilla) (Genus Chinchilla) | 105 | 115 | 110 | [24] |
Rodent (Chinese hamster) (Cricetulus griseus) | 21 | [6] | ||
Rodent (Chipmunk) (Subtribe Tamiina) | 31 | |||
Rodent (Cotton mouse) (Peromyscus gossypinus) | 23 | [6] | ||
Rodent (Coypu) (Myocastor coypus) | 132 | [5] | ||
Rodent (Crested porcupine) (Hystrix cristata) | 112 | [6] | ||
Rodent (Domestic guinea pig) (Cavia porcellus) | 56 | 74 | 65 | [17] |
Rodent (Domestic mouse) (Mus musculus) | 19 | [6] | ||
Rodent (Eastern gray squirrel) (Sciurus carolinensis) | 30 | 40 | 35 | |
Rodent (Golden hamster) (Mesocricetus auratus) | 16 | [6] | ||
Rodent (Greater Egyptian gerbil) (Gebrillus pyramidum) | 21 | [6] | ||
Rodent (Green acouchi) (Myoprocta pratti) | 98 | [6] | ||
Rodent (Hamster) (Subfamily Cricetinae) | 16 | 23 | 20 | |
Rodent (Hispid cotton rat) (Sigmodon hispidus) | 27 | [6] | ||
Rodent (Meadow mouse) (Microtus pennsylvanicus) | 21 | |||
Rodent (Mongolian gerbil) (Meriones unguiculatus) | 22 | 130 | 24 | [17] |
Rodent (Muskrat) (Ondatra zibethicus) | 28 | 30 | 29 | |
Rodent (North American porcupine) (Erethizon dorsatum) | 113 | [6] | ||
Rodent (Rat) (Genus Rattus) | 21 | 23 | 22 | [25] |
Rodent (Red squirrel) (Sciurus vulgaris) | 38 | [6] | ||
Rodent (Southern flying squirrel) (Glaucomys volans) | 40 | [6] | ||
Rodent (White-footed mouse) (Peromyscus leucopus) | 23 | [6] | ||
Skunk (Striped) (Mephitis mephitis) | 65 | [5] | ||
Sloth (Hoffmann's two-toed)) (Choloepus hoffmanni) | 355 | 377 | 366 | [26] |
Sloth (Pale-throated) (Bradypus tridactylus) | 183 | [27] | ||
Slow loris (Sunda) (Nycticebus coucang) | 90 | [6] | ||
Tapir (Malayan) (Acrocodia indica) | 379 | [5] | ||
Treeshrew (Common) (Tupaia glis) | 46 | [6] | ||
Whale (Beluga) (Delphinapterus leucas) | 408 | [5] | ||
Whale (Blue) (Balaenoptera musculus) | 305 | 365 | 335 | [28] |
Whale (Bottlenose dolphin) (Tursiops truncatus) | 364 | [5] | ||
Whale (Harbour porpoise) (Phocoena phocoena) | 270 | [6] | ||
Whale (Northern right whale dolphin) (Lissodelphis borealis) | 368 | 374 | 371 | [29] |
Whale (Orca) (Orcinus orca) | 473 | 567 | 532 | [30] |
Whale (Sperm) (Physeter catodon) | 480 | 590 | 535 | |
Whale (Spinner dolphin) (Stenella longirostris) | 318 | [5] |
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.[31] 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.[32] Large mammals require a longer period of time to attain any proportion of adult mass compared to small mammals.[33]
The level of development at birth
More developed infants will typically require a longer gestation period. Altricial mammals needs less time to gestate compare to the precocial (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.[34] Precocial mammal species generally have greater adult body weights than altricial mammals as precocial mammals have markedly longer gestation periods than altricial mammals.[35] 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.[36]
Environmental factor
In response to the conditions of the environment, some mammals, such as bat delay the implantation due to the cold temperature in winter.[37] 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.[38]
In pinnipeds, 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.[39]
See also
- Evolution of mammals - Timing of placental evolution
- Gestation
References
Citations
- ^ infoplease.com > Health and Science > Environment and Nature > Nature > Gestation, Incubation, and Longevity of Selected Animals By James G. Doherty, general curator, The Wildlife Conservation Society. Retrieved on April 9, 2010
- ^ van Aarde 1984, pp. 466–467
- ^ Gaudin, T. J.; Hicks, P.; Blanco, Y. D. (2018). "Myrmecophaga tridactyla (Pilosa: Myrmecophagidae)". Mammalian Species. 50 (956): 1–13. doi:10.1093/mspecies/sey001. hdl:11336/90534.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad Ardito, G. (1976). Check-list of the data on the gestation length of primates. Journal of human evolution, 5(2), 213-222.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag Langer, P. (2008). The phases of maternal investment in eutherian mammals. Zoology, 111(2), 148-162.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba Sacher, G. A., & Staffeldt, E. F. (1974). Relation of gestation time to brain weight for placental mammals: implications for the theory of vertebrate growth. The American Naturalist, 108(963), 593-615.
- ^ Greenhall, A.M.; Joermann, G.; Schmidt, U. (1983). "Desmodus rotundus" (PDF). Mammalian Species (202): 1–6. doi:10.2307/3503895. JSTOR 3503895. Archived (PDF) from the original on 2014-05-23. Retrieved 2011-11-29.
- ^ Fenton, M. Brock; Barclay, Robert M. R. (1980). "Myotis lucifugus". Mammalian Species (142): 1–8. doi:10.2307/3503792. JSTOR 3503792. S2CID 253932645.
- ^ University of Michigan. "Ursus Americanus". Retrieved 2013-01-16.
- ^ Kleiman, Devra G. "Giant Panda Reproduction". Archived from the original on 7 August 2008. Retrieved 14 April 2008.
- ^ "Pregnant cows, timing of pregnancy, open cows, pregnancy rate".
- ^ Paris Hill Farm. "Alpacas 101". Retrieved 2012-07-14.
- ^ Northwest Alpacas. "Alpaca Q&A". Archived from the original on 2012-07-21. Retrieved 2012-07-14.
- ^ Williamson, B. R. (1976). "Reproduction in female African elephant in the Wankie National Park, Rhodesia". South African Journal of Wildlife Research. 6 (2): 89–93.
- ^ Turkalo, A. K.; Fay, J. M. (2001). "African Rain Forest Ecology and Conservation. Observations from the Dzanga Saline". In Weber, W.; White, L. J. T.; Vedder, A.; Naughton-Treves, L. (eds.). African Rain Forest Ecology and Conservation: An Interdisciplinary Perspective. New Haven and London: Yale University Press. pp. 207–213. ISBN 9780300084337.
- ^ Johnson, Edward W.; Rasmussen, Lel (2002-07-01). "Morphological characteristics of the vomeronasal organ of the newborn Asian elephant (Elephas maximus)". The Anatomical Record. 267 (3): 252–259. doi:10.1002/ar.10112. ISSN 0003-276X. PMID 12115276. S2CID 30345793.
- ^ a b c d e Anamnese en lichamelijk onderzoek bij gezelschapsdieren, A.Rijnberk, F.J.van Sluis, 2nd print, Bohn Stafleu van Loghum, 2005, (Current Dutch veterinary examination study book for small domestic mammals)
- ^ a b Kiltie, R. A. (1982). Intraspecific variation in the mammalian gestation period. Journal of Mammalogy, 63(4), 646-652.
- ^ "Reproduction in free-ranging Florida manatees". National Biological Service Information and Technology Report 1.
- ^ Larry Vogelnest; Rupert Woods (August 18, 2008). Medicine of Australian Mammals. Csiro Publishing. p. 439. ISBN 978-0-643-09928-9.
- ^ . A timetable of embryonic development, and ovarian and uterine changes during pregnancy, in the stripe-faced dunnart, Sminthopsis macroura (Marsupialia: Dasyuridae). Journal of reproduction and fertility 91 1 (1991): 213-27. DOI 10.1530/jrf.0.0910213
- ^ Christian R. Abee; Keith Mansfield; Suzette D. Tardif; Timothy Morris, eds. (May 9, 2012). Nonhuman Primates in Biomedical Research: Biology and Management. Academic Press. p. 215. ISBN 978-0-12-397837-0.
- ^ Elephant seals. San Luis Obispo, Calif.: Central Coast Press. 1999. ISBN 9780965877695. OCLC 44446823.
- ^ A.Rijnberk, F.J (2005). Anamnese en lichamelijk onderzoek bij gezelschapsdieren, A.Rijnberk, F.J.van Sluis, 2nd print, Bohn Stafleu van Loghum, 2005, (Current Dutch veterinary examination study book for small domestic mammals)
- ^ The Laboratory Rat, 2nd Edition, Eds. Mark A. Sucklow, Steven H. Weisbroth, and Craig L. Franklin. Page 151.
- ^ Gilmore, D. P.; Da-Costa, C. P.; Duarte, D. P. F. (February 2000). "An update on the physiology of two- and three-toed sloths". Brazilian Journal of Medical and Biological Research. 33 (2): 129–146. doi:10.1590/S0100-879X2000000200001. ISSN 0100-879X. PMID 10657054.
- ^ Taube, E.; et al. (2001). "Reproductive biology and postnatal development in sloths, Bradypus and Choloepus: review with original data from the field (French Guiana) and from captivity". Mammalian Review. 31 (3–4): 173–188. Bibcode:2001MamRv..31..173T. doi:10.1111/j.1365-2907.2001.00085.x.
- ^ Sears, R.; Perrin, W. F. (2018). "Blue Whale: "Balaenoptera musculus"". In Würsig, B.; Thewissen, J. G. M.; Kovacs, K. M. (eds.). Encyclopedia of marine mammals. London, UK: Academic Press. pp. 110–114.
- ^ Larese, Jason P.; Chivers, Susan J. (2009). "Growth and reproduction of female eastern and whitebelly spinner dolphins incidentally killed in the eastern tropical Pacific tuna purse-seine fishery". Canadian Journal of Zoology. 87 (6): 537–552. Bibcode:2009CaJZ...87..537L. doi:10.1139/Z09-038. ISSN 0008-4301.
- ^ Frances M.D. Gulland; Leslie A. Dierauf; Karyl L. Whitman (20 March 2018). CRC Handbook of Marine Mammal Medicine. CRC Press. p. 408. ISBN 978-1-351-38416-2.
- ^ Sacher, G. A., & Staffeldt, E. F. (1974).Relation of gestation time to brain weight for placental mammals: implications for the theory of vertebrate growth. The American Naturalist, 108(963), 593-615.
- ^ Martin, R. D., Genoud, M., & Hemelrijk, C. K. (2005). Problems of allometric scaling analysis: examples from mammalian reproductive biology. Journal of Experimental Biology, 208(9), 1731-1747.
- ^ Zullinger, E. M., Ricklefs, R. E., Redford, K. H., & Mace, G. M. (1984). Fitting sigmoidal equations to mammalian growth curves. Journal of Mammalogy, 65(4), 607-636.
- ^ Martin, R. D., & MacLarnon, A. M. (1985). Gestation period, neonatal size and maternal investment in placental mammals. Nature, 313(5999), 220-223.
- ^ Derrickson, E. M. (1992). Comparative reproductive strategies of altricial and precocial eutherian mammals. Functional Ecology, 57-65.
- ^ Isler, K., & van Schaik, C. P. (2009). The expensive brain: a framework for explaining evolutionary changes in brain size. Journal of human evolution, 57(4), 392-400.
- ^ Racey, P. A., & Swift, S. M. (1981). Variations in gestation length in a colony of pipistrelle bats (Pipistrellus pipistrellus) from year to year. Reproduction, 61(1), 123-129.
- ^ Bradley, S. (2006). The ecology of bat reproduction.
- ^ Scheffer, V. B., & York, A. E. (1997). Timing of implantation in the northern fur seal, Callorhinus ursinus. Journal of Mammalogy, 78(2), 675-683.
Sources
- Gestation, Incubation, and Longevity of Selected Animals
- David Crystal, The Cambridge Factfinder Cambridge: Cambridge University Press, 1998 (84).
- Online animal encyclopedia
- Study finds wide range in pregnancy length
- van Aarde, Rudi J. (1984). "Aardvark". In Macdonald, David (ed.). The Encyclopedia of Mammals. New York, NY: Facts on File Publications. ISBN 978-0-87196-871-5.