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Thread: Morphological Evidence Supports Dryolestoid Affinities for the Living Australian Marsupial Mole Notoryctes

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    Senior Member Catterick's Avatar
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    Arrow Morphological Evidence Supports Dryolestoid Affinities for the Living Australian Marsupial Mole Notoryctes

    This is not really surprising. Originally they were thought to be monotremes. All they really shared with marsupials was epipubic bones which are primitive.

    https://peerj.com/preprints/755/

    Recent discoveries demonstrated that the southern continents were a cradle for the evolutionary radiation of dryolestoid mammals at the end of the Cretaceous. Moreover, it becomes evident that some of these early mammals surpassed the K/T boundary in South America, at least. Notoryctes is a poorly known living mammal, currently distributed in the deserts of central Australia. Due to its extreme modifications to fossoriality and peculiar anatomy, the phylogenetic relationships of this genus were debated in the past, but most recent authors agree in its marsupial affinities. A comparative survey of the anatomy of Notoryctes reveals the poorly sustained marsupial affinities for the genus and striking plesiomorphies for a living mammal. Surprisingly, Notoryctes exhibits similarities with dryolestoids. Dryolestoids were a diverse and mainly mesozoic mammalian group phylogenetically nested between the egg-lying monotremes and derived therians. In particular, Notoryctes share a number of shared features with the extinct dryolestoid Necrolestes, from the Miocene of Patagonia. Both taxa conform a clade of burrowing and animalivorous dryolestoids that survived other members of their lineage probably due to their peculiar habits. Accordingly, Notoryctes constitutes a “living-fossil” from the supposedly extinct dryolestoid radiation, extending the biochron of the group more than 20 million years to the present day. The intermediate phylogenetic position of Notoryctes has the pivotal potential to shed light on crucial anatomical, physiological, ecological, and evolutionary topics in the deep transformation from egg-lying to placental mammals. This finding, together with the Australian monotremes, constitutes the second example of early mammals that survived in Gondwana well after the KT boundary.

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    Senior Member Catterick's Avatar
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    This paper criticises molecular trees that miss fossil DNA (as in inevitable) because long branch attraction can suggest misleading relationships for taxa with no close relatives. You can't really test wether that is happening because there is no sampled DNA from mammals that are unambiguously non-therian and non-monotreme. But you can test the molecular tree against anatomical character states.

    You will notice (elsewhere) that Placental trees including morphological data from fossil taxa, have to be constrained to replicate clades supported by molecular evidence. Almost like the molecular data can be fallacious like any other kind of data.

    Not that anatomical cladistics is without flaws: without soft tissue or fossil taxa, Homo sapiens is the sister group to the bipedal Hylobatids (as supposed by Dubois...) and is not a great ape. However this becomes resolved by throwing in fossil hominoids or adding soft tissue states and the morphological evidence lines up with molecular evidence.

    Notice that the soft tissue states and fossils are what draw Notoryctes away from marsupials, not towards them.

    The philosophy of science and the psychology of what makes people choose one line of evidence over others are interesting. Moreso than what marsupial moles really are, which might never be resolved without aDNA or preserved soft tissue from relevant fossil mammals.

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