The current consensus is that the extinct rhipididstians are the ancestors of the tetrapods and that the transition took place no later than the mid-Devonian.
The Rhipidistians themselves are a loose polyphyletic assemblage whose exact lineage connections are not well established.
Some thought the Dipnoi and the tetrapods were sister groups with the Rhipidistians derived separately.
There is also a debate over whether tetrapods themselves
are monophyletic or polyphyletic; currently, it is generally accepted
that they are monophyletic
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