Darwinian Placental/Marsupial split:

Darwinists say that the three major lineages of class Mammalia shared a common ancestor approximately 161 to 217 mya .

The egg laying monotremes represent the earliest offshoot of the mammalian lineage & marsupial-placental mammal evolutionary divergence occured about160 million years ago.
[M. J. Phillips, T. H. Bennett, and M. S. Y. Lee, “Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas,” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 40, pp. 17089–17094, 2009 & Z. X. Luo, C. X. Yuan, Q. J. Meng, and Q. Ji, “A Jurassic eutherian mammal and divergence of marsupials and placentals,” Nature, vol. 476, no. 7361, pp. 442–445, 2011.]
http://www.popsci.co...marsupial-split

Darwinists consider this distinction to have come about early, and that each group lived its own evolutionary history totally independent of the other.

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The obstacle:

A most striking factor for consideration is the existence of numerous marsupial and placental mammals that are virtually identical to one another with the exception of the distinctions in their reproductive systems.
One of the most concrete examples of such an obstacle in the path of Neo-darwinian theory is that there are "pairs" in placentals and marsupials which are nearly the same.

In other words, according to the theory of evolution, mutations completely independent of each other must have produced these creatures "by chance" twice! This reality is a question that will give Darwinists problems even worse than dizzy spells.

Extraordinary resemblances and similar organs like these, which evolutionary biologists cannot accept as examples of "homology," show that homology does not constitute any evidence for the thesis of evolution from a common ancestor.