Editing Mammal (section)

===First mammals===

The [[Permian–Triassic extinction event]] about 252&nbsp;million years ago, which was a prolonged event due to the accumulation of several extinction pulses, ended the dominance of carnivorous therapsids.<ref>{{cite journal| vauthors = Tanner LH, Lucas SG, Chapman MG |title=Assessing the record and causes of Late Triassic extinctions |journal=Earth-Science Reviews |volume=65 |issue=1–2 |pages=103–139 |year=2004 |doi=10.1016/S0012-8252(03)00082-5 |url=https://nmnaturalhistory.org/pdf_files/TJB.pdf |bibcode=2004ESRv...65..103T |url-status=dead |archive-url=https://web.archive.org/web/20071025225841/http://nmnaturalhistory.org/pdf_files/TJB.pdf |archive-date=25 October 2007 }}</ref> In the early Triassic, most medium to large land carnivore niches were taken over by [[archosaur]]s<ref>{{cite journal | vauthors = Brusatte SL, Benton MJ, Ruta M, Lloyd GT | title = Superiority, competition, and opportunism in the evolutionary radiation of dinosaurs | journal = Science | volume = 321 | issue = 5895 | pages = 1485–1488 | date = September 2008 | pmid = 18787166 | doi = 10.1126/science.1161833 | bibcode = 2008Sci...321.1485B | hdl = 20.500.11820/00556baf-6575-44d9-af39-bdd0b072ad2b | s2cid = 13393888 | url = https://www.pure.ed.ac.uk/ws/files/8232088/PDF_Brusatteetal2008SuperiorityCompetition.pdf | access-date = 12 October 2019 | archive-date = 19 July 2018 | archive-url = https://web.archive.org/web/20180719005836/https://www.pure.ed.ac.uk/ws/files/8232088/PDF_Brusatteetal2008SuperiorityCompetition.pdf | url-status = live }}</ref> which, over an extended period (35&nbsp;million years), came to include the [[Crocodylomorpha|crocodylomorphs]],<ref>{{cite book | vauthors = Gauthier JA |year=1986 |chapter=Saurischian monophyly and the origin of birds |title=The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences | veditors = Padian K |volume=8 |publisher=California Academy of Sciences |location=San Francisco |pages=1–55}}</ref> the [[pterosaur]]s and the dinosaurs;<ref>{{cite journal| vauthors = Sereno PC |year=1991|title=Basal archosaurs: phylogenetic relationships and functional implications|journal=Memoirs of the Society of Vertebrate Paleontology|volume=2|pages=1–53|doi=10.2307/3889336|jstor=3889336}}</ref> however, large cynodonts like ''[[Trucidocynodon]]'' and [[Traversodontidae|traversodontids]] still occupied large sized carnivorous and herbivorous niches respectively. By the Jurassic, the dinosaurs had come to dominate the large terrestrial herbivore niches as well.<ref>{{cite journal| vauthors = MacLeod N, Rawson PF, Forey PL, Banner FT, Boudagher-Fadel MK, Bown PR, Burnett JA, Chambers P, Culver S, Evans SE, Jeffery C | display-authors = 6 |title=The Cretaceous–Tertiary biotic transition|year=1997|journal=Journal of the Geological Society|volume=154|issue=2|pages=265–292|doi=10.1144/gsjgs.154.2.0265|bibcode=1997JGSoc.154..265M | s2cid = 129654916 }}</ref>

The first mammals (in Kemp's sense) appeared in the Late Triassic epoch (about 225&nbsp;million years ago), 40&nbsp;million years after the first therapsids. They expanded out of their nocturnal [[insectivore]] niche from the mid-Jurassic onwards;<ref>{{cite book|url={{Google books|plainurl=yes|id=APWwBAAAQBAJ|page=73}}| vauthors = Hunt DM, Hankins MW, Collin SP, Marshall NJ |title=Evolution of Visual and Non-visual Pigments|year= 2014|location=London|publisher=Springer|page=73|isbn=978-1-4614-4354-4|oclc=892735337}}</ref> the Jurassic ''[[Castorocauda]]'', for example, was a close relative of true mammals that had adaptations for swimming, digging and catching fish.<ref>{{cite web | url=https://news.nationalgeographic.com/news/2006/02/0223_060223_beaver.html| archive-url=https://web.archive.org/web/20060303071809/http://news.nationalgeographic.com/news/2006/02/0223_060223_beaver.html| url-status=dead| archive-date=3 March 2006| vauthors = Bakalar N |year=2006| title=Jurassic "Beaver" Found; Rewrites History of Mammals|access-date=28 May 2016|work=National Geographic News}}</ref> Most, if not all, are thought to have remained nocturnal (the [[nocturnal bottleneck]]), accounting for much of the typical mammalian traits.<ref>{{cite journal | vauthors = Hall MI, Kamilar JM, Kirk EC | title = Eye shape and the nocturnal bottleneck of mammals | journal = Proceedings of the Royal Society B: Biological Sciences| volume = 279 | issue = 1749 | pages = 4962–4968 | date = December 2012 | pmid = 23097513 | pmc = 3497252 | doi = 10.1098/rspb.2012.2258 }}</ref> The majority of the mammal species that existed in the [[Mesozoic|Mesozoic Era]] were multituberculates, eutriconodonts and [[spalacotheriid]]s.<ref name=Luo2007>{{cite journal | vauthors = Luo ZX | title = Transformation and diversification in early mammal evolution | journal = Nature | volume = 450 | issue = 7172 | pages = 1011–1019 | date = December 2007 | pmid = 18075580 | doi = 10.1038/nature06277 | bibcode = 2007Natur.450.1011L | s2cid = 4317817 }}</ref> The earliest-known fossil of the [[Metatheria]] ("changed beasts") is ''[[Sinodelphys]]'', found in 125-million-year-old [[Early Cretaceous]] [[shale]] in China's northeastern [[Liaoning Province]]. The fossil is nearly complete and includes tufts of fur and imprints of soft tissues.<ref>{{cite web | url=https://news.nationalgeographic.com/news/2003/12/1215_031215_oldestmarsupial.html | archive-url=https://web.archive.org/web/20031217024049/http://news.nationalgeographic.com/news/2003/12/1215_031215_oldestmarsupial.html | url-status=dead | archive-date=17 December 2003 | vauthors = Pickrell J |year=2003| title=Oldest Marsupial Fossil Found in China| publisher=National Geographic News|access-date=28 May 2016}}</ref>

[[File:Juramaia NT.jpg|thumb|Restoration of ''[[Juramaia|Juramaia sinensis]]'', the oldest-known [[eutheria]]n (160 mya)<ref name=Juramaia/>]]

The oldest-known fossil among the [[Eutheria]] ("true beasts") is the small shrewlike ''[[Juramaia|Juramaia sinensis]]'', or "Jurassic mother from China", dated to 160&nbsp;million years ago in the late Jurassic.<ref name=Juramaia>{{cite journal | vauthors = Luo ZX, Yuan CX, Meng QJ, Ji Q | title = A Jurassic eutherian mammal and divergence of marsupials and placentals | journal = Nature | volume = 476 | issue = 7361 | pages = 442–5 | date = August 2011 | pmid = 21866158 | doi = 10.1038/nature10291 | bibcode = 2011Natur.476..442L | s2cid = 205225806 }}</ref> A later eutherian relative, ''[[Eomaia]]'', dated to 125&nbsp;million years ago in the early Cretaceous, possessed some features in common with the marsupials but not with the placentals, evidence that these features were present in the last common ancestor of the two groups but were later lost in the placental lineage.<ref>{{cite journal | vauthors = Ji Q, Luo ZX, Yuan CX, Wible JR, Zhang JP, Georgi JA | title = The earliest known eutherian mammal | journal = Nature | volume = 416 | issue = 6883 | pages = 816–822 | date = April 2002 | pmid = 11976675 | doi = 10.1038/416816a | bibcode = 2002Natur.416..816J | s2cid = 4330626 }}</ref> In particular, the [[epipubic bone]]s extend forwards from the pelvis. These are not found in any modern placental, but they are found in marsupials, monotremes, other nontherian mammals and ''[[Ukhaatherium]]'', an early Cretaceous animal in the eutherian order [[Asioryctitheria]]. This also applies to the multituberculates.<ref name="Epipubic bones in eutherian mammals">{{cite journal | vauthors = Novacek MJ, Rougier GW, Wible JR, McKenna MC, Dashzeveg D, Horovitz I | title = Epipubic bones in eutherian mammals from the late Cretaceous of Mongolia | journal = Nature | volume = 389 | issue = 6650 | pages = 483–486 | date = October 1997 | pmid = 9333234 | doi = 10.1038/39020 | bibcode = 1997Natur.389..483N | s2cid = 205026882 }}</ref> They are apparently an ancestral feature, which subsequently disappeared in the placental lineage. These epipubic bones seem to function by stiffening the muscles during locomotion, reducing the amount of space being presented, which placentals require to contain their [[fetus]] during gestation periods. A narrow pelvic outlet indicates that the young were very small at birth and therefore [[Pregnancy (mammals)|pregnancy]] was short, as in modern marsupials. This suggests that the placenta was a later development.<ref>{{cite book|chapter-url={{Google books|plainurl=yes|id=G1exWxU3QHIC|page=68}} | vauthors = Power ML, Schulkin J |year=2012|title=Evolution of the Human Placenta|publisher=Johns Hopkins University Press|location=Baltimore| isbn=978-1-4214-0643-5|page=68|chapter=Evolution of Live Birth in Mammals}}</ref>

One of the earliest-known monotremes was ''[[Teinolophos]]'', which lived about 120&nbsp;million years ago in Australia.<ref>{{cite journal | vauthors = Rowe T, Rich TH, Vickers-Rich P, Springer M, Woodburne MO | title = The oldest platypus and its bearing on divergence timing of the platypus and echidna clades | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 4 | pages = 1238–1242 | date = January 2008 | pmid = 18216270 | pmc = 2234122 | doi = 10.1073/pnas.0706385105 | bibcode = 2008PNAS..105.1238R | doi-access = free }}</ref> Monotremes have some features which may be inherited from the original amniotes such as the same orifice to urinate, defecate and reproduce ([[cloaca]])—as reptiles and birds also do—<ref>{{cite book|chapter-url={{Google books|plainurl=yes|id=FASJWgDhxIsC|page=55}}| vauthors = Grant T |year=1995|title=The Platypus: A Unique Mammal|chapter=Reproduction|publisher=University of New South Wales|location= Sydney|page=55|isbn=978-0-86840-143-0|oclc=33842474}}</ref> and they lay [[Egg (biology)|eggs]] which are leathery and uncalcified.<ref>{{cite journal | vauthors = Goldman AS | title = Evolution of immune functions of the mammary gland and protection of the infant | journal = Breastfeeding Medicine | volume = 7 | issue = 3 | pages = 132–142 | date = June 2012 | pmid = 22577734 | doi = 10.1089/bfm.2012.0025 }}</ref>