\[ **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. Human babies respond to the areola gland secretions from any lactating mother, not just their own; these secretions prompt them to open their mouths, put out their tongues, and suckle.]][^3] - see also: [[breastfeeding (chestfeeding)|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. Human babies respond to the areola gland secretions from any lactating mother, not just their own; these secretions prompt them to open their mouths, put out their tongues, and suckle.]][^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)]] [^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); Alex Riley, ‘[[Riley, ‘Pheromones Are Probably Not Why People Find You Attractive’, 2016|Pheromones Are Probably Not Why People Find You Attractive]]’, BBC, 9 May 2016, [https://www.bbc.com/future/article/20160509-the-tantalising-truth-about-sex-pheromones](https://www.bbc.com/future/article/20160509-the-tantalising-truth-about-sex-pheromones). [^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); Alex Riley, ‘[[Riley, ‘Pheromones Are Probably Not Why People Find You Attractive’, 2016|Pheromones Are Probably Not Why People Find You Attractive]]’, BBC, 9 May 2016, [https://www.bbc.com/future/article/20160509-the-tantalising-truth-about-sex-pheromones](https://www.bbc.com/future/article/20160509-the-tantalising-truth-about-sex-pheromones). [^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.