{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T09:15:29Z","timestamp":1785402929798,"version":"3.56.0"},"posted":{"date-parts":[[2026,3,8]]},"group-title":"Developmental Biology","reference-count":43,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,3,8]],"date-time":"2026-03-08T00:00:00Z","timestamp":1772928000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"id":[{"id":"https:\/\/ror.org\/001d55x84","id-type":"ROR","asserted-by":"publisher"}]},{"id":[{"id":"https:\/\/ror.org\/021nxhr62","id-type":"ROR","asserted-by":"publisher"}]},{"id":[{"id":"https:\/\/ror.org\/04v1psm68","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,3,8]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:p>\n                  Marsupials give birth to extremely altricial offspring which must be reared externally for an extended period, often in a pouch. Despite often being considered a defining feature of marsupials, around a third of living species lack a pouch. Here, we describe the postnatal development of the gray short-tailed opossum,\n                  <jats:italic>Monodelphis domestica<\/jats:italic>\n                  , a small pouchless South American didelphid and consider its implications for life history evolution within Metatheria. We find that at birth, ossification and chondrogenesis in neonatal\n                  <jats:italic>M. domestica<\/jats:italic>\n                  is more extensive than in basal pouched Australidelphian marsupials like the dunnart. Key precocial milestones such as tarsal ossification, eye opening, growth of body fur, and chewing tooth eruption occur earlier and more rapidly. Principal component analysis of life history and reproductive traits reveals a pronounced r- to K-selected gradient across living marsupial species. Stochastic character-mapping based ancestral state reconstruction suggests that absence of the pouch, and by inference possession of an r-selected life history strategy characterised by large litters, short attachment phases, and accelerated weaning was likely ancestral amongst crown-group marsupials. The more K-selected reproductive strategy of pouched marsupials wherein there is a prolonged postnatal development window, and relative few young are produced, likely evolved during the early Cenozoic, and separately amongst australidelphian and \u2018ameridelphian\u2019 marsupials. Rather than making early marsupials more sensitive to environmental disturbances, we hypothesis that their possession of an \u2018r-selected\u2019 life history strategy may have been a key factor in their persistence through the K\u2013Pg extinction.\n                <\/jats:p>","DOI":"10.64898\/2026.03.05.709990","type":"posted-content","created":{"date-parts":[[2026,3,9]],"date-time":"2026-03-09T04:30:51Z","timestamp":1773030651000},"source":"Crossref","is-referenced-by-count":0,"title":["Postnatal Development of the Gray Short-Tailed Opossum (\n                  <i>Monodelphis domestica<\/i>\n                  ): Implications for Metatherian Decline at the K\u2013Pg"],"prefix":"10.64898","author":[{"given":"Aidan M. C.","family":"Couzens","sequence":"first","affiliation":[{"name":"Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA"},{"name":"College of Science and Engineering, Flinders University, Bedford Park, South Australia 5042, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Clive","family":"Lau","sequence":"additional","affiliation":[{"name":"Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karen E.","family":"Sears","sequence":"additional","affiliation":[{"name":"Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026031105200454000_2026.03.05.709990v1.1","doi-asserted-by":"publisher","DOI":"10.1080\/106351599260472"},{"issue":"1-2","key":"2026031105200454000_2026.03.05.709990v1.2","first-page":"7","article-title":"Structure of the KT mammal radiation in North America: speculations on turnover rates and trophic structure","volume":"28","year":"1983","journal-title":"Acta Palaeontol. Pol"},{"issue":"1","key":"2026031105200454000_2026.03.05.709990v1.3","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1186\/1471-2105-7-88","article-title":"SIMMAP: Stochastic character mapping of discrete traits on phylogenies","volume":"7","year":"2006","journal-title":"BMC Bioinf"},{"key":"2026031105200454000_2026.03.05.709990v1.4","doi-asserted-by":"publisher","DOI":"10.1093\/jmammal\/gyx147"},{"key":"2026031105200454000_2026.03.05.709990v1.5","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.2006087117"},{"issue":"1","key":"2026031105200454000_2026.03.05.709990v1.6","doi-asserted-by":"crossref","first-page":"1028","DOI":"10.1038\/s42003-021-02506-2","article-title":"Postnatal development in a marsupial model, the fat-tailed dunnart (Sminthopsis crassicaudata; Dasyuromorphia: Dasyuridae)","volume":"4","year":"2021","journal-title":"Comm. Biol"},{"issue":"2","key":"2026031105200454000_2026.03.05.709990v1.7","first-page":"175","article-title":"The Weddell Line, an early Cenozoic biogeographical barrier among southern hemisphere terrestrial mammals","volume":"62","year":"2025","journal-title":"Ameghiniana"},{"issue":"1","key":"2026031105200454000_2026.03.05.709990v1.8","first-page":"41","article-title":"The marsupial pouch: implications for reproductive success and mammalian evolution","volume":"61","year":"2012","journal-title":"Aust. J. Zool"},{"key":"2026031105200454000_2026.03.05.709990v1.9","doi-asserted-by":"publisher","DOI":"10.1242\/dev.187633"},{"key":"2026031105200454000_2026.03.05.709990v1.10","doi-asserted-by":"publisher","DOI":"10.1093\/icb\/icw039"},{"issue":"5","key":"2026031105200454000_2026.03.05.709990v1.11","doi-asserted-by":"crossref","first-page":"349","DOI":"10.1111\/j.1096-3642.1955.tb00003.x","article-title":"The growth-stages of the pouch-young of the Native Cat (Dasyurus viverrinus) together with observations on the anatomy of the new-born young","volume":"28","year":"1955","journal-title":"Trans. Zool. Soc. London"},{"key":"2026031105200454000_2026.03.05.709990v1.12","doi-asserted-by":"publisher","DOI":"10.1002\/ece3.8114"},{"key":"2026031105200454000_2026.03.05.709990v1.13","doi-asserted-by":"crossref","unstructured":"Hughes RL , Hall LS . 1988. Structural adaptations of the newborn marsupial. In: Tyndale-Biscoe H, Janssens PA, editors. The Developing Marsupial. New York: Springer-Verlag. p 8\u201327.","DOI":"10.1007\/978-3-642-88402-3_2"},{"issue":"3","key":"2026031105200454000_2026.03.05.709990v1.14","first-page":"276","article-title":"The six-percent solution: second thoughts on the adaptedness of the Marsupialia","volume":"65","year":"1977","journal-title":"Am. Sci"},{"issue":"3","key":"2026031105200454000_2026.03.05.709990v1.15","first-page":"197","article-title":"The tectonic history of Drake Passage and its possible impacts on global climate","volume":"279","year":"2009","journal-title":"Earth Planet. Sci. Lett"},{"key":"2026031105200454000_2026.03.05.709990v1.16","doi-asserted-by":"publisher","DOI":"10.2307\/2407079"},{"issue":"4","key":"2026031105200454000_2026.03.05.709990v1.17","doi-asserted-by":"crossref","first-page":"691","DOI":"10.1017\/S0022336000032510","article-title":"Vertebrate faunal changes through Lancian and Puercan time in southern Wyoming","volume":"73","year":"1999","journal-title":"J. Paleontology"},{"key":"2026031105200454000_2026.03.05.709990v1.18","doi-asserted-by":"publisher","DOI":"10.1111\/j.1095-8312.1987.tb00434.x"},{"key":"2026031105200454000_2026.03.05.709990v1.19","doi-asserted-by":"publisher","DOI":"10.1038\/nature06277"},{"key":"2026031105200454000_2026.03.05.709990v1.20","doi-asserted-by":"publisher","DOI":"10.1038\/nature05805"},{"key":"2026031105200454000_2026.03.05.709990v1.21","doi-asserted-by":"publisher","DOI":"10.1093\/molbev\/msu176"},{"issue":"3","key":"2026031105200454000_2026.03.05.709990v1.22","doi-asserted-by":"crossref","first-page":"225","DOI":"10.1002\/bdra.23347","article-title":"Exogenous retinoic acid induces digit reduction in opossums (Monodelphis domestica) by disrupting cell death and proliferation, and apical ectodermal ridge and zone of polarizing activity function","volume":"103","year":"2015","journal-title":"Birth Def. Res"},{"issue":"5","key":"2026031105200454000_2026.03.05.709990v1.23","first-page":"843","article-title":"Modeling sunscreen-mediated melanoma prevention in the laboratory opossum (Monodelphis domestica)","volume":"27","year":"2014","journal-title":"Pig. Cell Mel. Res"},{"key":"2026031105200454000_2026.03.05.709990v1.24","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pbio.1000436"},{"key":"2026031105200454000_2026.03.05.709990v1.25","doi-asserted-by":"publisher","DOI":"10.1007\/s00239-003-0001-8"},{"key":"2026031105200454000_2026.03.05.709990v1.26","doi-asserted-by":"crossref","unstructured":"Nowak, R.M. , 1999. Walker\u2019s Mammals of the World Vol. 1. JHU Press.","DOI":"10.56021\/9780801857898"},{"key":"2026031105200454000_2026.03.05.709990v1.27","doi-asserted-by":"crossref","unstructured":"Renfree, M. B. and Pask, A. J. 2011. Reproductive and developmental manipulation of the marsupial, the tammar wallaby Macropus eugenii. In: Pelegri, F.J. editor. Vertebrate Embryogenesis, Methods in Molecular Biology 770.","DOI":"10.1007\/978-1-61779-210-6_18"},{"issue":"2","key":"2026031105200454000_2026.03.05.709990v1.28","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1111\/j.2041-210X.2011.00169.x","article-title":"phytools: an R package for phylogenetic comparative biology (and other things)","volume":"3","year":"2012","journal-title":"Meth. Ecol. Evol"},{"issue":"8","key":"2026031105200454000_2026.03.05.709990v1.29","doi-asserted-by":"crossref","first-page":"754","DOI":"10.1111\/2041-210X.12066","article-title":"Two new graphical methods for mapping trait evolution on phylogenies","volume":"4","year":"2013","journal-title":"Meth. Ecol. Evol"},{"key":"2026031105200454000_2026.03.05.709990v1.30","doi-asserted-by":"publisher","DOI":"10.1130\/B25402.1"},{"key":"2026031105200454000_2026.03.05.709990v1.31","doi-asserted-by":"publisher","DOI":"10.1111\/j.1525-142X.2008.00267.x"},{"issue":"10","key":"2026031105200454000_2026.03.05.709990v1.32","first-page":"2353","article-title":"Constraints on the morphological evolution of marsupial shoulder girdles","volume":"58","year":"2004","journal-title":"Evol"},{"issue":"5","key":"2026031105200454000_2026.03.05.709990v1.33","doi-asserted-by":"crossref","first-page":"1663","DOI":"10.1111\/j.1558-5646.1997.tb01489.x","article-title":"Comparative patterns of craniofacial development in eutherian and metatherian mammals","volume":"51","year":"1997","journal-title":"Evol"},{"key":"2026031105200454000_2026.03.05.709990v1.34","doi-asserted-by":"publisher","DOI":"10.1002\/ar.24049"},{"key":"2026031105200454000_2026.03.05.709990v1.35","doi-asserted-by":"crossref","unstructured":"Tyndale-Biscoe, C.H. , 2005. Life of Marsupials. CSIRO Publishing.","DOI":"10.1071\/9780643092204"},{"key":"2026031105200454000_2026.03.05.709990v1.36","doi-asserted-by":"crossref","unstructured":"Tyndale-Biscoe, C.H. and Renfree, M. , 1987. Reproductive Physiology of Marsupials. Cambridge University Press.","DOI":"10.1017\/CBO9780511623493"},{"key":"2026031105200454000_2026.03.05.709990v1.37","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pbio.3000494"},{"key":"2026031105200454000_2026.03.05.709990v1.38","doi-asserted-by":"publisher","DOI":"10.1086\/720410"},{"issue":"11","key":"2026031105200454000_2026.03.05.709990v1.39","doi-asserted-by":"crossref","first-page":"e26826","DOI":"10.1371\/journal.pone.0026826","article-title":"Spontaneous development of full weight-supported stepping after complete spinal cord transection in the neonatal opossum, Monodelphis domestica","volume":"6","year":"2011","journal-title":"PLOS ONE"},{"key":"2026031105200454000_2026.03.05.709990v1.40","doi-asserted-by":"publisher","DOI":"10.1016\/j.cub.2023.04.009"},{"key":"2026031105200454000_2026.03.05.709990v1.41","doi-asserted-by":"publisher","DOI":"10.3897\/zookeys.465.8178"},{"key":"2026031105200454000_2026.03.05.709990v1.42","doi-asserted-by":"publisher","DOI":"10.1666\/12041"},{"issue":"1","key":"2026031105200454000_2026.03.05.709990v1.43","doi-asserted-by":"crossref","first-page":"13734","DOI":"10.1038\/ncomms13734","article-title":"A large carnivorous mammal from the Late Cretaceous and the North American origin of marsupials","volume":"7","year":"2016","journal-title":"Nature Comm"}],"container-title":[],"original-title":[],"link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.64898\/2026.03.05.709990","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,3,11]],"date-time":"2026-03-11T12:20:24Z","timestamp":1773231624000},"score":1,"resource":{"primary":{"URL":"http:\/\/biorxiv.org\/lookup\/doi\/10.64898\/2026.03.05.709990"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,8]]},"references-count":43,"URL":"https:\/\/doi.org\/10.64898\/2026.03.05.709990","relation":{},"subject":[],"published":{"date-parts":[[2026,3,8]]},"subtype":"preprint"}}