Beck Robin M D, Godthelp Henk, Weisbecker Vera, Archer Michael, Hand Suzanne J
School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia.
PLoS One. 2008 Mar 26;3(3):e1858. doi: 10.1371/journal.pone.0001858.
We describe new cranial and post-cranial marsupial fossils from the early Eocene Tingamarra Local Fauna in Australia and refer them to Djarthia murgonensis, which was previously known only from fragmentary dental remains.
METHODOLOGY/PRINCIPAL FINDINGS: The new material indicates that Djarthia is a member of Australidelphia, a pan-Gondwanan clade comprising all extant Australian marsupials together with the South American microbiotheres. Djarthia is therefore the oldest known crown-group marsupial anywhere in the world that is represented by dental, cranial and post-cranial remains, and the oldest known Australian marsupial by 30 million years. It is also the most plesiomorphic known australidelphian, and phylogenetic analyses place it outside all other Australian marsupials.
CONCLUSIONS/SIGNIFICANCE: As the most plesiomorphic and oldest unequivocal australidelphian, Djarthia may approximate the ancestral morphotype of the Australian marsupial radiation and suggests that the South American microbiotheres may be the result of back-dispersal from eastern Gondwana, which is the reverse of prevailing hypotheses.
我们描述了来自澳大利亚始新世早期廷加马拉动物群的新的有袋类颅骨和颅后化石，并将它们归为莫尔贡贾西亚兽，此前该物种仅发现过零散的牙齿化石。
方法/主要发现：新材料表明，贾西亚兽是澳大利亚有袋总目动物的一员，这是一个泛冈瓦纳分支，包括所有现存的澳大利亚有袋类动物以及南美洲的小负鼠科动物。因此，贾西亚兽是世界上已知最古老的有袋类冠群动物，有牙齿、颅骨和颅后化石为证，也是已知最古老的澳大利亚有袋类动物，比其他同类早3000万年。它也是已知最原始的澳大利亚有袋总目动物，系统发育分析显示它在所有其他澳大利亚有袋类动物之外。
结论/意义：作为最原始、最古老且明确无误的澳大利亚有袋总目动物，贾西亚兽可能接近澳大利亚有袋类动物辐射演化的祖先形态类型，并表明南美洲的小负鼠科动物可能是从冈瓦纳东部反向扩散的结果，这与主流假设相反。
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