Editing Morganucodon (section)

==Biology==

[[File:Morganucodon.jpg|left|thumb|[[Life restoration]] of ''M. oehleri'']]
[[File:Morganucodon skull.svg|left|thumb|Diagram of the skull of ''Morganucodon'', with bones labelled ]]
''Morganucodon'' was a small, [[plantigrade]] animal. The tail was moderately long. According to Kemp (2005), "the skull was 2–3 cm in length and a presacral body length of about 10 cm [4 inches]. In general appearance, it would have looked like a shrew or mouse".<ref>Kemp T.S. 2005. ''The origin and evolution of mammals'', Oxford University Press, page 143. {{ISBN|0-19-850760-7}}.</ref> There is evidence that it had specialized glands used for grooming, which may indicate that, like present day mammals, it had fur.<ref name=Fur>{{cite journal| last1=Ruben|first1= J.A. |last2= Jones| first2= T.D. |year=2000|title= Selective Factors Associated with the Origin of Fur and Feathers |journal=[[Integrative and Comparative Biology|American Zoologist]]|volume= 40|pages= 585–596 | doi = 10.1093/icb/40.4.585| issue=4 |doi-access= free}}</ref>

Like present-day mammals of similar size and presumed habit, ''Morganucodon'' was likely nocturnal and spent the day in a burrow. There is no direct fossil evidence, but several lines of evidence point to a [[nocturnal bottleneck]] in the evolution of the mammal class, and almost all modern mammals of similar size to ''Morganucodon'' are still nocturnal.<ref>{{cite journal|last1=Hall|first1=M. I.|last2=Kamilar|first2=J. M.|last3=Kirk|first3=E. C.|title=Eye shape and the nocturnal bottleneck of mammals|journal=Proceedings of the Royal Society B: Biological Sciences|date=24 October 2012|volume=279|issue=1749|pages=4962–4968|doi=10.1098/rspb.2012.2258|pmid=23097513|pmc=3497252}}</ref><ref>{{cite journal|last1=Muchlinski|first1=Magdalena N.|title=A comparative analysis of vibrissa count and infraorbital foramen area in primates and other mammals|journal=Journal of Human Evolution|date=June 2010|volume=58|issue=6|pages=447–473|doi=10.1016/j.jhevol.2010.01.012|pmid=20434193}}</ref> Likewise, burrowing was widespread both in non-mammalian [[cynodont]]s and in primitive mammals.<ref>{{cite journal|last1=Damiani|first1=R.|last2=Modesto|first2=S.|last3=Yates|first3=A.|last4=Neveling|first4=J.|title=Earliest evidence of cynodont burrowing|journal=Proceedings of the Royal Society B: Biological Sciences|date=22 August 2003|volume=270|issue=1525|pages=1747–1751|doi=10.1098/rspb.2003.2427|pmid=12965004|pmc=1691433}}</ref><ref>{{cite journal |last1=Kielan-Jaworowska |first1=Zofia |author-link=Zofia Kielan-Jaworowska |last2=Gambaryan |first2=Petr P. |name-list-style=and |date=December 1994 |title=Postcranial anatomy and habits of Asian multituberculate mammals |journal=Lethaia |volume=27 |issue=4 |pages=300 |doi=10.1111/j.1502-3931.1994.tb01578.x |s2cid=85021289}}</ref> The logics of [[phylogenetic bracketing]] would make ''Morganucodon'' nocturnal and burrowing too. Plant material from the conifer ''[[Hirmeriella]]'' was also found in the fissure fills, indicating ''Morganucudon'' lived in, or near, a forested area.

The diet appears to have been insects and other small animals, with a preference for hard prey such as beetles.<ref>{{cite journal |last1=Gill |first1=Pamela G.  |last2=Purnell |first2=Mark A. |last3=Crumpton |first3=Nick |author-link4=Kate Robson Brown|last4=Robson-Brown |first4=Kate |last5=Gostling |first5=Neil J. |last6=Stampanoni |first6=M. |last7=Rayfield |first7=Emily J. |date=21 August 2014 |title=Dietary specializations and diversity in feeding ecology of the earliest stem mammals |journal=[[Nature (journal)|Nature]] |volume=512 |issue=7514 |pages=303–305 |doi=10.1038/nature13622 |pmid=25143112  |bibcode=2014Natur.512..303G |hdl=2381/29192  |s2cid=4469841 |hdl-access=free }}</ref> Like most modern mammal insectivores, it grew fairly quickly to adult size.<ref>{{cite journal |last=Chinsamy |first=A. |last2=Hurum |first2=J.H. |year=2006 |title=Bone microstructure and growth patterns of early mammals |url=http://www.app.pan.pl/archive/published/app51/app51-325.pdf |journal=Acta Palaeontologica Polonica |volume=51 |issue=2 |pages=325–338 |access-date=30 August 2013}}</ref> Its eggs were probably small and leathery, a condition still found in monotremes.<ref>{{cite journal |last=Parente |first=Raphael Câmara Medeiros |last2=Bergqvist |first2=Lílian Paglarelli |last3=Soares |first3=Marina Bento |last4=Filho |first4=Olimpio Barbosa Moraes |year=2011 |title=The history of vaginal birth |journal=Archives of Gynecology and Obstetrics |volume=284 |issue=1 |pages=1–11 |doi=10.1007/s00404-011-1918-6 |pmid=21547459 |s2cid=22997887}}</ref>

The teeth grew in mammalian fashion, with [[deciduous teeth]] being replaced by permanent teeth that were retained throughout the rest of the animal's life.<ref name=Replace>Alexander F. H. van Nievelt and Kathleen K. Smith, "To replace or not to replace: the significance of reduced functional tooth replacement in marsupial and placental mammals", ''Paleobiology'', Volume 31, Issue 2 (June 2005) pages 324–346</ref> The combination of rapid growth in juveniles and a toothless stage at infancy strongly suggests that ''Morganucodon'' raised its young by [[lactation]]; indeed, it may have been among the first animals to do so.<ref>{{cite book |last1=Kielan-Jaworowska |first1=Zofia |author-link=Zofia Kielan-Jaworowska |title=Mammals from the age of dinosaurs : origins, evolution, and structure |last2=Cifelli |first2=Richard L. |last3=Luo |first3=Zhe-Xi |date=2004 |publisher=Columbia University Press |isbn=978-0231119184 |location=New York |pages=148–153}}</ref> The molars in the adult had a series of raised humps and edges that fit into each other, allowing for efficient chewing. However, unlike the situation in most later mammals, the upper and lower molars did not occlude properly when they first met; as they wore against each other, however, their shapes were modified by wear to produce a precise fit.<ref>{{cite journal |last1=Crompton |first1=A. W. |last2=Jenkins |first2=Farish A. Jr. |author-link2=Farish Jenkins |year=1968 |title=Molar occlusion in late Triassic mammals |journal=Biological Reviews |volume=43 |issue=4 |pages=427–458 |doi=10.1111/j.1469-185x.1968.tb00966.x |pmid=4886687 |s2cid=1044399}}</ref>

A 2020 study suggests that the metabolism of ''Morganucodon'' was significantly slower than that of comparably sized modern mammals, and that it had a life-span more similar to that of reptiles, with the oldest specimen having a lifespan of 14 years. Thus it likely did not possess the fully [[endotherm]]ic metabolism seen in current mammals.<ref>{{cite journal |last1= Newham |first1=Elis |last2=Gill |first2=Pamela |display-authors=1 |date=2020 |title=Reptile-like physiology in Early Jurassic stem-mammals |journal=Nature Communications |volume=11 |issue=1 |pages=5121 |doi=10.1038/s41467-020-18898-4 |pmid=33046697 |pmc=7550344 |bibcode=2020NatCo..11.5121N |doi-access=free}}</ref>