Editing Mammal (section)

===Definitions {{Anchor|variations}}===
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The word "[[:wikt:mammal|mammal]]" is modern, from the scientific name ''Mammalia'' coined by [[Carl Linnaeus]] in 1758, derived from the [[Latin language|Latin]] ''[[wikt:mamma#Latin|mamma]]'' ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia [[phylogenetically]] as the [[crown group]] of mammals, the [[clade]] consisting of the [[most recent common ancestor]] of living [[monotreme]]s ([[echidna]]s and [[platypus]]es) and [[theria]]ns ([[marsupial]]s and [[placental]]s) and all descendants of that ancestor.<ref>{{cite journal |vauthors=Rowe T |year=1988 |title=Definition, diagnosis, and origin of Mammalia |journal=Journal of Vertebrate Paleontology |volume=8 |issue=3 |pages=241–264 |url=https://www.geo.utexas.edu/faculty/rowe/Publications/pdf/010%20Rowe%201988.pdf |doi=10.1080/02724634.1988.10011708 |bibcode=1988JVPal...8..241R |access-date=25 January 2024 |archive-date=18 January 2024 |archive-url=https://web.archive.org/web/20240118163712/http://www.geo.utexas.edu/faculty/rowe/Publications/pdf/010%20Rowe%201988.pdf |url-status=live }}</ref> Since this ancestor lived in the [[Jurassic]] period, Rowe's definition excludes all animals from the earlier [[Triassic]], despite the fact that Triassic fossils in the [[Haramiyida]] have been referred to the Mammalia since the mid-19th century.<ref>{{cite book |title=The Student's Elements of Geology | vauthors = Lyell C |author-link=Charles Lyell |year=1871 |publisher=John Murray |location=London |page=347 |url={{Google books|plainurl=yes|id=634gAQAAIAAJ|page=347}} |isbn=978-1-345-18248-4}}</ref> If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. ''[[Ambondro mahabo|Ambondro]]'' is more closely related to monotremes than to therian mammals while ''[[Amphilestes]]'' and ''[[Amphitherium]]'' are more closely related to the therians; as fossils of all three genera are dated about {{ma|167|million years ago}} in the [[Middle Jurassic]], this is a reasonable estimate for the appearance of the crown group.<ref>{{cite journal |vauthors=Cifelli RL, Davis BM |title=Paleontology. Marsupial origins |journal=Science |volume=302 |issue=5652 |pages=1899–1900 |date=December 2003 |pmid=14671280 |doi=10.1126/science.1092272|s2cid=83973542 }}</ref>

[[T. S. Kemp]] has provided a more traditional definition: "[[Synapsid]]s that possess a [[dentary]]–[[squamosal bone|squamosal]] jaw articulation and [[occlusion (dentistry)|occlusion]] between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view, the clade originating with the last common ancestor of ''[[Sinoconodon]]'' and living mammals.<ref>{{cite book |url=https://doc.rero.ch/record/200125/files/PAL_E3904.pdf |location=United Kingdom |title=The Origin and Evolution of Mammals |vauthors=Kemp TS |year=2005 |publisher=Oxford University Press |isbn=978-0-19-850760-4 |page=3 |oclc=232311794 |access-date=25 January 2024 |archive-date=26 September 2023 |archive-url=https://web.archive.org/web/20230926060152/https://doc.rero.ch/record/200125/files/PAL_E3904.pdf |url-status=live }}</ref> The earliest-known synapsid satisfying Kemp's definitions is ''[[Tikitherium]]'', dated {{ma|225|Ma}}, so the appearance of mammals in this broader sense can be given this [[Late Triassic]] date.<ref>{{cite journal |vauthors=Datta PM |year=2005 |title=Earliest mammal with transversely expanded upper molar from the Late Triassic (Carnian) Tiki Formation, South Rewa Gondwana Basin, India |journal=Journal of Vertebrate Paleontology |volume=25 |issue=1 |pages=200–207 |doi=10.1671/0272-4634(2005)025[0200:EMWTEU]2.0.CO;2|s2cid=131236175 }}</ref><ref>{{cite journal | vauthors = Luo ZX, Martin T |year=2007 |title=Analysis of Molar Structure and Phylogeny of Docodont Genera |journal=Bulletin of Carnegie Museum of Natural History |volume=39 |pages=27–47 |doi=10.2992/0145-9058(2007)39[27:AOMSAP]2.0.CO;2 |s2cid=29846648 |url=https://xa.yimg.com/kq/groups/13543816/1018125207/name/Luo+y+Martin+2007-+molar+structure+and+phylogeny+of+docodonts.pdf |access-date=8 April 2013 |archive-url=https://web.archive.org/web/20160303225517/http://xa.yimg.com/kq/groups/13543816/1018125207/name/Luo+y+Martin+2007-+molar+structure+and+phylogeny+of+docodonts.pdf |archive-date=3 March 2016 |url-status=dead }}</ref> However, this animal may have actually evolved during the Neogene.<ref name=":3">{{Cite journal |last1=Averianov |first1=Alexander O. |last2=Voyta |first2=Leonid L. |date=March 2024 |title=Putative Triassic stem mammal Tikitherium copei is a Neogene shrew |url=https://link.springer.com/10.1007/s10914-024-09703-w |journal=Journal of Mammalian Evolution |language=en |volume=31 |issue=1 |doi=10.1007/s10914-024-09703-w |issn=1064-7554}}</ref>