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Updated: May 24, 2025
The earliest known remains of mammals are those of small marsupials, which are the lowest of the mammalian type; while, conversely, the highest of the mammalian type Man is the most recent. The evidence that the vertebrate fauna, as a whole, has become more heterogeneous, is considerably stronger.
These limbless reptiles, evolved by degeneration from lizardlike ancestors, appeared in nonpoisonous types scarcely to be distinguished from those of the present day. The higher mammals had appeared, and henceforth the lower mammals the monotremes and the marsupials are reduced to a subordinate place. These first true mammals were archaic and generalized in structure.
The earliest fossil remains of them were found in the latest Triassic strata lower jaws of small ungulates and marsupials. More numerous remains are found a little later in the Jurassic, and some in the Cretaceous. All the mammal remains that we have from this section belong to the lower promammals and marsupials; among these were most certainly the ancestors of the human race.
And, as before the shooting of kangaroos, wallabies, and opossums was resorted to as a means of livelihood by hundreds of bushmen who had no other employment open to them, the young of these marsupials furnished the iguana with an ample supply of food, the theory is very probably correct.
In the first stages of the Tertiary period, in the age when we begin to trace the evolution of the suck-giving animals above the lowly grade in which the kangaroos and opossums belong, we find the ancestors of our mammalian series all characterized by rather weakly organized limbs fitted, as were those of their remoter kindred the marsupials, for tree climbing rather than for moving over the surface of the ground.
In the same way their affinities are seen to be with the lowest of mammals, the MONOTREMES and MARSUPIALS. The monotremes, such as the duckbill mole and the spiny ant-eater of Australia, reproduce by means of eggs resembling those of reptiles; the marsupials, such as the opossum and the kangaroo, bring forth their young alive, but in a very immature condition, and carry them for some time after birth in the marsupium, a pouch on the ventral side of the body.
Amongst other points Professor Huxley called attention to the resemblance between the anterior molars of the placental dog with those of the marsupial thylacine. These, indeed, are strikingly similar, but there are better examples still of this sort of coincidence. Thus it has often been remarked that the insectivorous marsupials, e.g.
They are placed by the mother in a marsupial pouch on her ventral surface, and here nourished till able to care for themselves. Pardon a moment's digression. The marsupials, except the opossum, are confined to Australia, and the oviparous mammals, or monotremes, to New Zealand.
It is said to have only a single young one at a time, and my own observation confirms this statement, for I once shot a female with a very small blind and naked little creature clinging closely to its breast, which was quite bare and much wrinkled, reminding me of the young of Marsupials, to which it seemed to form a transition.
Not only can we not find them, but zoological science tells us that they never existed, for the 'feebly pronounced, the ineffectual, marsupials of Australia and New Zealand could never have survived a competition with better creatures, such as that by which they are now perishing.
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