“Marsupionta”的意思、由来-开放百科全书

'Marsupionta' is a hypothesised subclass within the Mammalia group. The existence of Marsupionta is a postulation by some researchers as a category devolving upon a notional unification between Marsupials (Marsupial/Marsupialia, Metatheria) with the egg-laying monotremes (Monotremata, Protheria). Under this suggested classification, placental mammals (Eutheria) would be the sister subclass to Marsupionta. The Marsupionta hypothesis was proposed in 1947 by W.K. Gregory^[1] and has since been the subject of multiple studies.^[2]^[3]^[4]

This merging of marsupials and monotremes into the hypothesized subclass of Marsupionta is contrary to the widespread belief that pouch and placental mammals share the common subclass Theria that excludes monotremes. Under this scheme that splits the marsupials from the monotremes, monotremes are placed by themselves in the subclass Yinotheria. Yinotheria are characterised by a number of common derived characteristics (synapomorphies), which include among others, viviparia (the birth of live pups), the presence of teats, and several features in the skull and shoulder girdle structures.

Common morphological features of the Marsupionta exist only in the epipubic (pouch) bones. The two epipubic bones that protrude from the pelvis bone, are present in both monotremes and marsupials, but are missing in placentals. However, some primitive mammals, as well as fossil ancestors of the Cretaceous higher mammals also exhibit these bones. It can therefore be assumed that the epipubic bones were an original feature that has been reduced in today's placentals, and thus no morphological feature for the Marsupionta exists.

Genetic findings regarding the correct classification scheme for marsupials and monotremes are contradictory. Comparisons of mitochondrial DNA support the Marsupionta theory,^[5] while genome sequencing^[6] speaks for the Theria hypothesis. Other studies do not come to a clear conclusion. The majority of researchers prefer the Theria classification based on the morphologies of marsupials and monotremes.

References

1. ^{{Cite journal|title=The root of the mammalian tree inferred from whole mitochondrial genomes|language=en|citeseerx = 10.1.1.518.7974}}
2. ^{{Cite journal|title=Phylogenetic analysis of 1.5 Mbp and platypus EST data refute the Marsupionta hypothesis and unequivocally support Monotremata as sister group to Marsupialia/Placentalia|journal=Zoologica Scripta|volume=37|issue=2|pages=115–127|language=en|doi = 10.1111/j.1463-6409.2007.00319.x|year = 2008|last1 = Kullberg|first1 = Morgan|last2=Hallström|first2=Björn M|last3=Arnason|first3=Ulfur|last4=Janke|first4=Axel}}
3. ^{{Cite journal|title=Marsupials and Eutherians reunited: genetic evidence for the Theria hypothesis of mammalian evolution|journal= Mammalian Genome|volume=12|issue=7|pages=513–7|language=en|pmid = 11420613|year = 2001|last1 = Killian|first1 = J. K|last2=Buckley|first2=T. R|last3=Stewart|first3=N|last4=Munday|first4=B. L|last5=Jirtle|first5=R. L|doi=10.1007/s003350020026}}
4. ^{{Cite journal|title=The platypus is in its place: nuclear genes and indels confirm the sister group relation of monotremes and Therians|journal=Molecular Biology and Evolution|volume=23|issue=3|pages=587–97|language=en|pmid = 16291999|year = 2006|last1 = Van Rheede|first1 = T|last2=Bastiaans|first2=T|last3=Boone|first3=D. N|last4=Hedges|first4=S. B|last5=De Jong|first5=W. W|last6=Madsen|first6=O|doi=10.1093/molbev/msj064}}
5. ^{{Cite journal|last=Janke |first=Axel|last2=Magnell|first2=Ola |display-authors=etal |date=2002|title=Phylogenetic Analysis of 18S rRNA and the Mitochondrial Genomes of the Wombat, Vombatus ursinus, and the Spiny Anteater, Tachyglossus aculeatus; Increased Support for the Marsupionta Hypothesis|url=https://www.researchgate.net/publication/11621274|journal=J. Mol. Evol.|volume=54|issue=1|pages=71–80|via=ResearchGate|pmid=11734900|doi=10.1007/s00239-001-0019-8}}
6. ^{{Cite journal|last=Grützner|first=Frank|last2=Graves|first2=Jeniffer A. Marshall|date=2004|title=A platypus' eye view of the mammalian genome|url=http://uahost.uantwerpen.be/funmorph/raoul/fylsyst/Grutzner2004.pdf|journal=Curr. Opin. Genet. Dev.|volume=14|pages=642–649|via=University of Antwerp}}