Hi MJ,
I don't want this post to be part of a pile-on, but I am hoping a new thread can be originated to discuss the idea you have mentioned several times in this thread. I think it could be a very interesting discussion.
MJ writes:
It is likely that each of the species that you mention are representative of kinds that are no longer well represented - the other member species disappeared by extinction. In these cases, the sloth or the kangaroo likely are the lone living representatives of their respective kinds, thus they are isolated taxonomically or whatever your method of classification.
This idea is quite congruent with evolutionary thought on the subject. The vast majority of species that have ever existed on the planet are extinct. We have a number of lineages that are represented by one or at best a very few species today, that were clearly more numerous in the past. If you could identify a group of obviously related organisms in the fossil record, using your
bauplan or whatever other criteria you choose, you might be able to show the diversity bulge that this scenario you propose would require (i.e., original kind => diversity of related sub-kinds (or whatever term you use) => single modern remnant). It might be a very good way to show empirical support for your concept. Have you uncovered any examples of this?
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