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  • The Gondwanan Origin of Tribosphenida (Mammalia)

    From erik simpson@21:1/5 to All on Sun Dec 25 09:11:58 2022
    Title from https://www.tandfonline.com/doi/full/10.1080/03115518.2022.2132288

    Abstract

    A review of the Southern Hemisphere Mesozoic tribosphenic mammal fossil record supports the hypothesis that Tribosphenida arose in the Southern Hemisphere during the Early Jurassic, around 50 million years prior to the clade’s reliably dated first
    appearance in the Northern Hemisphere. Mesozoic Southern Hemisphere tribosphenic mammals are known from Australia, Madagascar, South America and the Indian subcontinent, and are classified into three families: Bishopidae (fam. nov.), Ausktribosphenidae
    and Henosferidae. These are stem therians, and considerable morphological evolution occurred within the lineage between the Jurassic and late Early Cretaceous. Important dental modifications include a graduated transition between premolars and molars,
    development of molar wear facets V and VI, loss of facets for postdentary bones, reduction in the Meckelian groove and development of a true dentary angle. Previous classifications of Southern Hemisphere tribosphenic mammals are ambiguous because
    information from the upper dentition has been lacking. Upper molars attributed to the late Early Cretaceous (Albian) Southern Hemisphere group Bishopidae fam. nov. are now known to possess a prominent protocone and stylar cusp C. We thus consider
    bishopids to be the sister group to Theria.

    This strongly suggests the origin of Tribosphenida was in the Jurassic, and
    in the southern hemisphere. (The prevailing understanding is that the group was more or less synonymous with Boreosphenida (see https://en.wikipedia.org/wiki/Tribosphenida)

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  • From jillery@21:1/5 to eastside.erik@gmail.com on Mon Dec 26 02:54:21 2022
    On Sun, 25 Dec 2022 09:11:58 -0800 (PST), erik simpson <eastside.erik@gmail.com> wrote:

    Title from https://www.tandfonline.com/doi/full/10.1080/03115518.2022.2132288

    Abstract

    A review of the Southern Hemisphere Mesozoic tribosphenic mammal fossil record supports the hypothesis that Tribosphenida arose in the Southern Hemisphere during the Early Jurassic, around 50 million years prior to the clade’s reliably dated first
    appearance in the Northern Hemisphere. Mesozoic Southern Hemisphere tribosphenic mammals are known from Australia, Madagascar, South America and the Indian subcontinent, and are classified into three families: Bishopidae (fam. nov.), Ausktribosphenidae
    and Henosferidae. These are stem therians, and considerable morphological evolution occurred within the lineage between the Jurassic and late Early Cretaceous. Important dental modifications include a graduated transition between premolars and molars,
    development of molar wear facets V and VI, loss of facets for postdentary bones, reduction in the Meckelian groove and development of a true dentary angle. Previous classifications of Southern Hemisphere tribosphenic mammals are ambiguous
    because information from the upper dentition has been lacking. Upper molars attributed to the late Early Cretaceous (Albian) Southern Hemisphere group Bishopidae fam. nov. are now known to possess a prominent protocone and stylar cusp C. We thus
    consider bishopids to be the sister group to Theria.

    This strongly suggests the origin of Tribosphenida was in the Jurassic, and >in the southern hemisphere. (The prevailing understanding is that the group was more or less synonymous with Boreosphenida (see https://en.wikipedia.org/wiki/Tribosphenida)


    This is interesting to me. I understood mammal dentition to be a
    defining characteristic of mammalian clades. But IIUC your cited
    Wikipedia article, tribosphenic molars are found in several
    paraphyletic groups. Are there other molar types which were once
    considered diagnostic of a clade but are no longer?

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  • From Sight Reader@21:1/5 to All on Mon Dec 26 07:19:18 2022
    Is it me or does it seem like you have to be absolutely obsessed with dentistry to study post-Triassic mammals?

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    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From erik simpson@21:1/5 to 69jp...@gmail.com on Mon Dec 26 08:38:59 2022
    On Sunday, December 25, 2022 at 11:54:24 PM UTC-8, 69jp...@gmail.com wrote:
    On Sun, 25 Dec 2022 09:11:58 -0800 (PST), erik simpson
    <eastsi...@gmail.com> wrote:

    Title from https://www.tandfonline.com/doi/full/10.1080/03115518.2022.2132288

    Abstract

    A review of the Southern Hemisphere Mesozoic tribosphenic mammal fossil record supports the hypothesis that Tribosphenida arose in the Southern Hemisphere during the Early Jurassic, around 50 million years prior to the clade’s reliably dated first
    appearance in the Northern Hemisphere. Mesozoic Southern Hemisphere tribosphenic mammals are known from Australia, Madagascar, South America and the Indian subcontinent, and are classified into three families: Bishopidae (fam. nov.), Ausktribosphenidae
    and Henosferidae. These are stem therians, and considerable morphological evolution occurred within the lineage between the Jurassic and late Early Cretaceous. Important dental modifications include a graduated transition between premolars and molars,
    development of molar wear facets V and VI, loss of facets for postdentary bones, reduction in the Meckelian groove and development of a true dentary angle. Previous classifications of Southern Hemisphere tribosphenic mammals are ambiguous
    because information from the upper dentition has been lacking. Upper molars attributed to the late Early Cretaceous (Albian) Southern Hemisphere group Bishopidae fam. nov. are now known to possess a prominent protocone and stylar cusp C. We thus
    consider bishopids to be the sister group to Theria.

    This strongly suggests the origin of Tribosphenida was in the Jurassic, and >in the southern hemisphere. (The prevailing understanding is that the group was more or less synonymous with Boreosphenida (see https://en.wikipedia.org/wiki/Tribosphenida)
    This is interesting to me. I understood mammal dentition to be a
    defining characteristic of mammalian clades. But IIUC your cited
    Wikipedia article, tribosphenic molars are found in several
    paraphyletic groups. Are there other molar types which were once
    considered diagnostic of a clade but are no longer?

    I'm not that well-versed in the mammal fossil record of the Mesozoic. For a long time teeth
    were the major part of that record, but my impression is that more recent finds have opened
    things up some. Just glancing at phylogentic tree found by googling shows lots of polytomies
    and short-branched clades. The overall view is pretty consistent, but there are lots of clades
    that are less well-supported than you'd like.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From erik simpson@21:1/5 to thesigh...@gmail.com on Mon Dec 26 08:39:36 2022
    On Monday, December 26, 2022 at 7:19:20 AM UTC-8, thesigh...@gmail.com wrote:
    Is it me or does it seem like you have to be absolutely obsessed with dentistry to study post-Triassic mammals?

    I don't know if it's absolutely necessary, but an awful lot of the post-Triasssic mammal fossils are little jaws and
    teeth. Mammals made a run for it in the Triassic, but following the end-Triassic extinction the dinosaurs got
    the upper hand, and mammals hunkered down until the end-Cretaceous event gave them another chance.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)