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      Three new Jurassic euharamiyidan species reinforce early divergence of mammals

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      Nature

      Springer Science and Business Media LLC

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          Abstract

          The phylogeny of Allotheria, including Multituberculata and Haramiyida, remains unsolved and has generated contentious views on the origin and earliest evolution of mammals. Here we report three new species of a new clade, Euharamiyida, based on six well-preserved fossils from the Jurassic period of China. These fossils reveal many craniodental and postcranial features of euharamiyidans and clarify several ambiguous structures that are currently the topic of debate. Our phylogenetic analyses recognize Euharamiyida as the sister group of Multituberculata, and place Allotheria within the Mammalia. The phylogeny suggests that allotherian mammals evolved from a Late Triassic (approximately 208 million years ago) Haramiyavia-like ancestor and diversified into euharamiyidans and multituberculates with a cosmopolitan distribution, implying homologous acquisition of many craniodental and postcranial features in the two groups. Our findings also favour a Late Triassic origin of mammals in Laurasia and two independent detachment events of the middle ear bones during mammalian evolution.

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          Most cited references 28

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          An Early Cretaceous tribosphenic mammal and metatherian evolution.

           Xi Yuan,  Zhe Luo,  Qiang Ji (2003)
          Derived features of a new boreosphenidan mammal from the Lower Cretaceous Yixian Formation of China suggest that it has a closer relationship to metatherians (including extant marsupials) than to eutherians (including extant placentals). This fossil dates to 125 million years ago and extends the record of marsupial relatives with skeletal remains by 50 million years. It also has many foot structures known only from climbing and tree-living extant mammals, suggesting that early crown therians exploited diverse niches. New data from this fossil support the view that Asia was likely the center for the diversification of the earliest metatherians and eutherians during the Early Cretaceous.
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            The earliest known eutherian mammal.

            The skeleton of a eutherian (placental) mammal has been discovered from the Lower Cretaceous Yixian Formation of northeastern China. We estimate its age to be about 125 million years (Myr), extending the date of the oldest eutherian records with skull and skeleton by about 40 50 Myr. Our analyses place the new fossil at the root of the eutherian tree and among the four other known Early Cretaceous eutherians, and suggest an earlier and greater diversification of stem eutherians that occurred well before the molecular estimate for the diversification of extant placental superorders (104 64 Myr). The new eutherian has limb and foot features that are known only from scansorial (climbing) and arboreal (tree-living) extant mammals, in contrast to the terrestrial or cursorial (running) features of other Cretaceous eutherians. This suggests that the earliest eutherian lineages developed different locomotory adaptations, facilitating their spread to diverse niches in the Cretaceous.
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              A Late Jurassic digging mammal and early mammalian diversification.

               Zhe Luo,  J Wible (2005)
              A fossil mammal from the Late Jurassic Morrison Formation, Colorado, has highly specialized teeth similar to those of xenarthran and tubulidentate placental mammals and different from the generalized insectivorous or omnivorous dentitions of other Jurassic mammals. It has many forelimb features specialized for digging, and its lumbar vertebrae show xenarthrous articulations. Parsimony analysis suggests that this fossil represents a separate basal mammalian lineage with some dental and vertebral convergences to those of modern xenarthran placentals, and reveals a previously unknown ecomorph of early mammals.
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                Author and article information

                Journal
                Nature
                Nature
                Springer Science and Business Media LLC
                0028-0836
                1476-4687
                October 2014
                September 10 2014
                October 2014
                : 514
                : 7524
                : 579-584
                Article
                10.1038/nature13718
                25209669
                © 2014

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