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Re: On the subject of mysterious absences...The Answer

We have a winner:

The error involves Premise 1 and Premise 2. Premise 1 is using the word "amphibean" to describe a specific group of creatures including frogs, toads, salamanders, and various other existing groups. Premise 2 is using the term in a much broader sense, to include lineages which have long been extinct- basically, any tertrapod which is/was not an amniote (is that correct? I'm no scientist).


Today's amphibians (Lissamphibia) are probably more closely related to us than the anthracosaurs are. Using Amphibia for "all tetrapods that aren't amniotes" obscures this.

The same premises also contain further, related errors, assumed within the
error described:

1: The assumption that traits nearly universal among living representatives
of a group must have been near-universal among extinct members of that group
(most living dinosaurs can fly, therefor most dinosaurs must have been able
to fly).

Yes. In reality, the argument I reproduced was not so much made with anthracosaurs as with temnospondyls, which were universally thought to be amphibians in the phylogenetic sense ( = closer to Lissamphibia than we are), but that still didn't make the argument valid, as we are now finding out.

2: Defining a group in part by exclusion- as taking amphibeans to mean, as stated, any tetrapod which is not an amniote, and then expecting any member of this group to by more like another memebr of the group in every way than like any member of the excluded group (both apatosaurs and dromeaosaurs were non-avian dinosaurs, therefor the must have both walked on the same number
of legs).

Yes. This is what I meant. The same risk applies to Thecodontia.