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Updated: May 24, 2025
In Austro-Columbia, the later Tertiary fauna exhibits numerous and varied forms of Platyrrhine Apes, Rodents, Cats, Dogs, Stags, Edentata, and Opossums; but, as at present, no Catarrhine Apes, no Lemurs, no Insectivora, Oxen, Antelopes, Rhinoceroses, nor Didelphia other than Opossums.
At the epoch of the Trias, therefore, the Marsupialia must have, already existed long enough to have become differentiated into carnivorous and herbivorous forms. But the Monotremata are lower forms than the Didelphia, which last are intercalary between the Ornithodelphia and the Monodelphia.
But if this be the case, how much further back must we go to find the common stock of the monodelphous Mammalia? As to the Didelphia, if we may trust the evidence which seems to be afforded by their very scanty remains, a Hypsiprymnoid form existed at the epoch of the Trias, contemporaneously with a Carnivorous form.
But the three sub-classes differ so widely from each other, not only in the construction of the sexual organs, but in many other respects also, that we may confidently draw up the following important phylogenetic thesis: The Monodelphia or Placentals descend from the Didelphia or Marsupials; and the latter, in turn, are descended from the Monotremes or Ornithodelphia.
Triassic. : 21. Monotrema. Promammalia. : 21. Ornithodelphia. Echidna. Ornithorhyncus. Jurassic. : 22. Marsupalia. Prodidelphia. : 22. Didelphia. Didelphys. Perameles. Cretaceous. : 23. Mallotheria. Prochoriata. : 23. Insectivora. Erinaceida. Older Eocene. : 24. Lemuravida. Older lemurs. Dentition. 3. 1. 4. 3. : 24. Pachylemures. Neo-Eocene. : 25. Lemurogona. Later lemurs.
In Austro-Columbia the later Tertiary fauna exhibits numerous and varied forms of Platyrrhine Apes, Rodents, Cats, Dogs, Stags, Edentata, and Opossums; but, as at present, no Catarrhine Apes, no Lemurs, no Insectivora, Oxen, Antelopes, Rhinoceroses, nor Didelphia other than Opossums.
That the Didelphia were developed out of some ornithodelphous form, as Professor Haeckel supposes, seems to be unquestionable; but the existing Opossums and Kangaroos are certainly extremely modified and remote from their ancestors the "Prodidelphia," of which we have not, at present the slightest knowledge.
At the epoch of the Trias, therefore, the Marsupialia must have already existed long enough to have become differentiated into carnivorous and herbivorous forms. But the Monotremata are lower forms than the Didelphia which last are intercalary between the Ornithodelphia and the Monodelphia.
But if this be the case, how much further back must we go to find the common stock of the monodelphous Mammalia? As to the Didelphia, if we may trust the evidence which seems to be afforded by their very scanty remains, a Hypsiprymnoid form existed at the epoch of the Trias, contemporaneously with a Carnivorous form.
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