\[ **BT: [[chordates]]** ] --- # mammals ## characteristics of mammals ### lactation [[Mammals are distinguished by their ability to nurse their young.]][^1] [[Lactation has been a crucial factor in the evolution of mammalian parental investment and reproductive strategies.]][^2] [[There might be a 'human mammary pheromone, suggested by the response of human babies to secretions from any lactating mother, not just their own. Babies suck in response to secretions from the areola gland around the nipple.']][^3] - see also: [[breastfeeding (chestfeeding) 1|breastfeeding/chestfeeding]] #### oxytocin [[Suckling induces oxytocin production in all mammals.]][^4] [[In rabbits, the amount of oxytocin produced when suckling is correlated with litter size.]][^5] #### lactation and circadian rhythm [[Rats nurse more during the day time (i.e. their sleep and rest time).]][^1] - see also: [[life#circadian rhythms|circadian rhythms]] ### mammal pheromones [[Some mammals make use of appeasement (calming) pheromones.]][^6] [[There might be a 'human mammary pheromone, suggested by the response of human babies to secretions from any lactating mother, not just their own. Babies suck in response to secretions from the areola gland around the nipple.']][^7] - see also: [[pheromones]] --- ## classification of mammals | MAMMALIA Subclasses | Infraclass | Subdivision | Order | Notes | | --------------------------------------- | ------------------------------- | ------------------------------------------ | ------------------------------ | ---------------------------------------------------------- | | **YINOTHERIA**<br>\[egg-laying mammals] | | **Monotremata**<br>\[egg-laying mammals] | Monotremata | echidnas | | | | | | playtpus | | | | | | | | **THERIA**<br>\[live-bearing mammals] | **METATHERIA**<br>\[marsupials] | **Marsupialia**<br>\[pouch-based mammals] | Dasyuromorphia | Tasmanian tiger | | | | | Didelphimorphia | | | | | | Diprotodontia | | | | | | Microbiotheria | | | | | | Notoryctemorphia | | | | | | Paucituberculata | | | | | | Peramelemorphia | | | | | | † Yalkaparidontia | | | | | | | | | | **EUTHERIA**<br>\[placentals] | **Placentalia**<br>\[uterus-based mammals] | Afrosoricida | | | | | | [[artiodactyls\|Artiodactyla]] | antelope, cattle, sheep | | | | | [[carnivorans\|Carnivora]] | | | | | | | | | | | | | | | | | | | | | | | | Chiroptera | bats | | | | | Cingulata | | | | | | Dermoptera | | | | | | Eulipotyphla | true insectivores (hedgehogs, gymures, moles, true shrews) | | | | | Hyracoidea | | | | | | [[lagomorphs\|Lagomorpha]] | rabbits, hares, pika | | | | | Macroscelidea | | | | | | Perissodactyla | | | | | | Pholidota | | | | | | Pilosa | | | | | | [[primates\|Primates]] | primates | | | | | Proboscidea | | | | | | [[rodents\|Rodentia]] | rodents | | | | | Scandentia | | | | | | Sirenia | | | | | | Tubulidentata | | [^8] ## therians One of two mammal subclasses. Therians include Metatherians (aligns with Marsupialia) and Eutherians (aligns with Placentalia).[^9] ### therian XX/XY sex determination system [[Most therian mammals have a very conserved XX-XY sex determination system.]][^10] [[The general standard, in XY organisms, is two copies of the X chromosome in females (XX), and one X and one Y (XY) in males.]][^11] ### eutherians/placentals - [[artiodactyls|Artiodactyla (Order)]] - [[carnivorans|Carnivora (Order)]] - [[primates|Primates (Order)]] - [[rodents|Rodentia (Order)]] ## endnotes [^1]: Avery Nelson Gilbert, ‘[[Gilbert, ‘Mammary Number and Litter Size in Rodentia’, 1986|Mammary Number and Litter Size in Rodentia: The “One-Half Rule”]]’, *Proceedings of the National Academy of Sciences of the United States of America*, vol. 83, no. 13 (1986), p. 4828, https://www.jstor.org/stable/27601?origin=JSTOR-pdf. [^2]: Avery Nelson Gilbert, ‘[[Gilbert, ‘Mammary Number and Litter Size in Rodentia’, 1986|Mammary Number and Litter Size in Rodentia: The “One-Half Rule”]]’, *Proceedings of the National Academy of Sciences of the United States of America*, vol. 83, no. 13 (1986), p. 4828, https://www.jstor.org/stable/27601?origin=JSTOR-pdf. [^3]: Tristram D. Wyatt, ‘[[Wyatt, ‘Pheromones’, 2017|Pheromones]]’, *Current Biology*, vol. 27, no. 15 (2017), R743, [https://doi.org/10.1016/j.cub.2017.06.039](https://doi.org/10.1016/j.cub.2017.06.039). [^4]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 4, https://doi.org/10.3389/fendo.2018.00106; Jennifer Denver, *[[Denver, Female Biology, 2024|Female Biology]]*, 2nd edition, All USF Faculty Authored Books 108 (2024), p. 354. USF Scholarship Repository, https://repository.usfca.edu/faculty_books_all/108; Cat Bohannon, *[[Bohannon, Eve, 2023|Eve: How the Female Body Drove 200 Million Years of Human Evolution]]* (Hutchinson Heinemann, 2023), p. 43. [^5]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 4, https://doi.org/10.3389/fendo.2018.00106. [^6]: ’Pheromone’, Wikipedia, last edited 4 January 2025, 02:41 (UTC), https://en.wikipedia.org/wiki/Pheromone. [^7]: Tristram D. Wyatt, ‘[[Wyatt, ‘Pheromones’, 2017|Pheromones]]’, *Current Biology*, vol. 27, no. 15 (2017), R743, [https://doi.org/10.1016/j.cub.2017.06.039](https://doi.org/10.1016/j.cub.2017.06.039). [^8]: ‘Mammal’, Wikipedia, last edited 31 October 2025, 07:19 (UTC), https://en.wikipedia.org/wiki/Mammal. [^9]: Frédéric Veyrunes et al., ‘[[Veyrunes et al., ‘A Novel Sex Determination System in a Close Relative of the House Mouse’, 2010|A Novel Determination System in a Close Relative of the House Mouse]]’, *Proceedings of the Royal Society B (Biological Sciences)*, vol. 277, no. 1684, p. 1049, https://doi.org/10.1098/rspb.2009.1925. [^10]: Frédéric Veyrunes et al., ‘[[Veyrunes et al., ‘A Novel Sex Determination System in a Close Relative of the House Mouse’, 2010|A Novel Determination System in a Close Relative of the House Mouse]]’, *Proceedings of the Royal Society B (Biological Sciences)*, vol. 277, no. 1684, p. 1049, https://doi.org/10.1098/rspb.2009.1925. [^11]: Frédéric Veyrunes et al., ‘[[Veyrunes et al., ‘A Novel Sex Determination System in a Close Relative of the House Mouse’, 2010|A Novel Determination System in a Close Relative of the House Mouse]]’, *Proceedings of the Royal Society B (Biological Sciences)*, vol. 277, no. 1684, p. 1049, https://doi.org/10.1098/rspb.2009.1925.