Editing Multituberculata (section)

== Description ==
[[File:Taeniolabis NT small.jpg|thumb|left|Restoration of ''[[Taeniolabis]]'', the largest multituberculate at approximately {{convert|22|kg|abbr=on}}.]]
The multituberculates had a cranial and dental anatomy superficially similar to rodents such as mice and rats, with cheek-teeth separated from the chisel-like front teeth by a wide tooth-less gap (the [[Diastema (dentistry)|diasteme]]). Each cheek-tooth displayed several rows of small cusps (or [[tubercle]]s, hence the name) that operated against similar rows in the teeth of the jaw; the exact homology of these cusps to [[theria]]n ones is still a matter of debate.{{citation needed|date=June 2020}} Unlike rodents, which have ever-growing teeth, multituberculates underwent dental replacement patterns typical of most mammals (though in at least some species the lower incisors continued to erupt long after the root's closure).<ref name="p. 299">[[Zofia Kielan-Jaworowska|Kielan-Jaworowska, Zofia]], Richard L. Cifelli, and Zhe-Xi Luo (2005). ''Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure '', [https://books.google.com/books?id=qJGcX3X0EaMC&pg=PA299 p. 299]</ref> Multituberculates are notable for the presence of a massive fourth lower premolar, the [[plagiaulacoid]]; other mammals, like [[Plesiadapiformes]] and [[diprotodontia]]n [[marsupials]], also have similar premolars in both upper and lower jaws, but in multituberculates this tooth is massive and the upper premolars are not modified this way. In basal multituberculates all three lower premolars were plagiaulacoids, increasing in size posteriorly, but in [[Cimolodonta]] only the fourth lower premolar remained, with the third one remaining only as a vestigial peg-like tooth,<ref name="p. 299"/> and in several taxa like [[taeniolabidoidea]]ns, the plagiaulacoid disappeared entirely or was reconverted into a molariform tooth.<ref>Gurovich 2005 p. 334{{full citation needed|date=September 2021}}</ref><ref name="Gurovich & Beck 2009">{{cite journal |last1=Gurovich |first1=Yamila |last2=Beck |first2=Robin |date=March 2009 |title=The Phylogenetic Affinities of the Enigmatic Mammalian Clade Gondwanatheria |journal=Journal of Mammalian Evolution |volume=16 |issue=1 |pages=25–49 |doi=10.1007/s10914-008-9097-3 |s2cid=42799370}}</ref><ref>Rougier et al. 2009 p.233{{full citation needed|date=September 2021}}</ref>

[[File:Ptilodus skull BW.jpg|thumb|Skull of ''[[Ptilodus]]''. Notice the massive blade-like lower premolar.]]

Unlike rodents and similar therians, multituberculates had a palinal jaw stroke (front-to-back), instead of a propalinal (back-to-front) or transverse (side-to-side) one; as a consequence, their jaw musculature and cusp orientation is radically different.<ref name="Agusti-3" /><ref name="p. 299"/> Palinal jaw strokes are almost entirely absent in modern mammals (with the possible exception of the [[dugong]]<ref>{{cite journal |last1=Lanyon |first1=J. M. |last2=Sanson |first2=G. D. |title=Degenerate dentition of the dugong (Dugong dugon), or why a grazer does not need teeth: morphology, occlusion and wear of mouthparts |journal=Journal of Zoology |date=February 2006 |volume=268 |issue=2 |pages=133–152 |doi=10.1111/j.1469-7998.2005.00004.x }}</ref>), but are also present in [[haramiyida]]ns, [[argyrolagoidea]]ns and [[tritylodontid]]s, the former historically united with multituberculates on that basis. Multituberculate mastication is thought to have operated in a two stroke cycle: first, food held in place by the last upper premolar was sliced by the bladelike lower pre-molars as the dentary moved orthally (upward). Then the lower jaw moved palinally, grinding the food between the molar cusp rows.<ref name="Agusti-3" /><ref name="p. 299"/>
[[File:American Jurassic Mammals plate VII.jpg|thumb|Lower jaws and teeth of [[Allodontidae|allodontid]] multituberculates]]

The structure of the [[pelvis]] in the Multituberculata suggests that they gave birth to tiny helpless, underdeveloped young, similar to modern [[marsupial]]s, such as kangaroos.<ref name="Weil" /><ref name="p. 299"/> However, a 2022 study reveals that they might actually have had long gestation periods like placentals.<ref>{{cite web | url=https://news.umich.edu/new-study-challenges-old-views-on-whats-primitive-in-mammalian-reproduction/ | title=New study challenges old views on what's 'primitive' in mammalian reproduction | date=25 July 2022 }}</ref> However, in 2024, all Allotheria (including multituberculates) fell outside the crown group of Mammalia, implying that cimolodonts developed placental-like gestation (and viviparity in general) independently, rather than multituberculates and therians having a common viviparous ancestor.<ref>{{Cite journal |last=Mao |first=Fangyuan |last2=Li |first2=Zhiyu |last3=Wang |first3=Zhili |last4=Zhang |first4=Chi |last5=Rich |first5=Thomas |last6=Vickers-Rich |first6=Patricia |last7=Meng |first7=Jin |date=2024-04-03 |title=Jurassic shuotheriids show earliest dental diversification of mammaliaforms |url=https://www.nature.com/articles/s41586-024-07258-7 |journal=Nature |language=en |doi=10.1038/s41586-024-07258-7 |issn=0028-0836|url-access=subscription }}</ref>

At least two lineages developed [[hypsodonty]], in which tooth enamel extends beyond the gumline: [[Lambdopsalis|lambdopsalid]] [[taeniolabidoidea]]ns<ref name=willbru>{{cite journal|last1=Williamson|first1=Thomas E.|last2=Brusatte|first2=Stephen L.|last3=Secord|first3=Ross|last4=Shelley|first4=Sarah|title=A new taeniolabidoid multituberculate (Mammalia) from the middle Puercan of the Nacimiento Formation, New Mexico, and a revision of taeniolabidoid systematics and phylogeny|journal=Zoological Journal of the Linnean Society|volume=177|pages=183–208|date=2015|doi=10.1111/zoj.12336|doi-access=free}}</ref> and [[sudamericid]] [[gondwanatheres]].<ref>{{Cite web|url=https://books.google.com/books?id=JgKGv2aQxggC&q=gondwanatheria+grass&pg=PA32|title=Gondwanatheria}}{{dead link|date=September 2021}}</ref>

Studies published in 2018 demonstrated that multituberculates had relatively complex brains, some braincase regions even absent in therian mammals.<ref>{{cite journal |last1=Crompton |first1=A. W. |last2=Musinsky |first2=C. |last3=Rougier |first3=G. W. |last4=Bhullar |first4=B.-A. S. |last5=Miyamae |first5=J. A. |title=Origin of the Lateral Wall of the Mammalian Skull: Fossils, Monotremes and Therians Revisited |journal=Journal of Mammalian Evolution |date=September 2018 |volume=25 |issue=3 |pages=301–313 |doi=10.1007/s10914-017-9388-7 |s2cid=16072755 }}</ref>