>>Yeah... I messed up the amniota there.
>>
>>Birds and frogs are a monophyletic group with all of the amniotes except birds removed, and all of the anamniote tetrapods except frogs removed.>>

One way to test monophyly is to use taxonomic characters. Monophyletic groups are united by synapomorphies, or shared derived characters. Example, the monophyletic group called Aves is united by the synapomorphy of feathers. Polyphyletic groups are united by convergent characters. For example, the polyphyletic group Haemothermia is defined on the basis of the convergent character homeothermy. Paraphyletic groups are defined by symplesiomorphs or shared ancestral characters. For example, Anapsida is defined by the shared ancestral state of an unfenestrated skull.

Please propose either a sympleisomorph or a synapomorph, either morphological or molecular, that would define your monophyletic/paraphyletic group "frogs plus birds." Otherwise you have no evidence to assert your claim of monophyly or paraphyly for this group.

Let me start first, your group frogs plus birds form a polyphyletic group because they share the convergent character of fewer than 5 fingers (frogs have 4 and birds have 3). Frogs have fingers 1-2-3-4, whereas birds have fingers 2-3-4. Since the closest relative of birds, the crocs, have five fingers, it follows that the last common ancestor of the frogs, crocs and birds probably had 5 fingers. That means frogs and birds lost their fingers independently after they last shared a common ancestor. Hence birds are only convergently similar to frogs and the two thus form a polyphyletic group.

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