Depends on the size of the saltation, I would think. Is it hypothesized to explain every gap in the record? And if we find an intermediate fossil, does that falsify the saltation or just make two where there was previously one?
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Yes, this is another way in which itâs too vague to be useful.
This would have certain consequences for phylogenetic reconstruction: you would see a tree that has a flurry of branches (a massive polytomy), with one branch later giving rise to another polytomy, and one of those to a further polytomy, etc. But this tends not to be what we see. Polytomies tend to have only a few branches, and most of the tree is generally found to be bifurcating. Of course you would have to identify a specific hypothesis of groups descended from these stem species, without prior reference to a tree, in order to test it. But identifying even one group that arose through saltation, or one that didnât, seems beyond you.
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Yes, of course, especially if youâre thinking about the record in any one area. And the distribution of taxa being limited in space as well as time, it does little good if the time missing from point A is found half-way around the world at point B.
I should add that the fossil record doesnât even have to be missing in some area; a change in environment could locally eliminate many species that continue to survive in some unsampled region, or show the sudden appearance of many species that could have been found in that unsampled area.
As @Roy and @AnEvolvedPrimate said, thatâs basically evolution. How does it differ? I suppose it might differ in the way @John_Harshman suggests, with a series of massive polytomies, but I took your âexplodesâ term to simply mean an adaptive radiation of the type we typically see in the fossil record, which would not require any polytomy. (And, of course, heâs right. We donât see huge polytomies, and thatâs probably because they are not real but are artifacts of the limits of our evidence; if two bifurcating events happen closely together, itâs not necessarily possible to say which of them happened first.)
Itâs fair to say that the fossil record does show adaptive radiations. They tend to be the product of ecological opportunity and things like that â for example, you get a huge mammalian adaptive radiation after the dominant large fauna are comprehensively exterminated in the K-Pg event. But the fact that adaptive radiations happen is not a challenge to, but rather an illustration of, evolutionary processes. And so I am having considerable difficulty seeing how your âstem speciesâ notion is different from conventional evolutionary explanation at all.
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Thatâs because itâs so vague as to be compatible with almost anything. I suspect his model has some unstated features: most importantly, that God causes the saltations and that otherwise they would be impossible; also, I do think he envisages a stem species giving rise to many independent saltatory events, pretty much all at once.
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Yeah, that seems to be true. And it means that one can carry on never defending a position, because thereâs no position to defend, while contending that the scientists have got it wrong. I donât know about Giltil, but Iâd be very unhappy to find myself in that sort of nihilistic zone. Surely at some point, if one cares about the origins of living diversity at all, one has got to have some kind of idea or understanding of the ideas of others which can be characterized meaningfully.
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To the ID-proponents and creationists, this was never really about getting the history of life on Earth right. It was always about trying to create some sort of platform on which to instigate a deeply socially conservative and fundamentalist religious revolution.
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One possible difference is that in @Giltilâs rocket scenario, every âexplosionâ, i.e. diversification, is on a single lineage, rather than each lineage having the potential to radiate independently of the others. Rather like the great chain of being, instead of the evolutionary bush. So the âexplosionâ that resulted in the radiation of bird species would have to be on the same lineage as the radiation of mammals, for example - and the same lineage as the radiation of flowering plants. Though itâs also possible that he, like many creationists, simply doesnât know or care about any lineage other than the one leading to humans.
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Well, yes. But I still might think that individuals who take a particular interest in the âcontroversyâ would want to have SOME idea beyond a mere negation of evolution as to what they think happened (and happens). I know that if I somehow came to believe in extreme saltationism, I would think that a thorough familiarity with the fossil record would be the first thing I would try to learn. I cannot imagine advocating for that view for years without ever bothering. It would be embarrassing to be constantly caught short of relevant facts.
Iâve lost count of the creation/ID advocates Iâve seen who are completely unembarrassed when caught posting vagaries, blather, falsehoods, copied rubbish, miswuotes or even outright lies.
Itâs as if being ârightâ (aka invincible incompetence) means never having to say sorry.
Iâd like to point out that @Giltil has posed a hypothesis that appears to be testable (perhaps with some modifications already suggested). So itâs probably wrong, but this too is science. 
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Has he? Shouldnât it make an explicitly, concrete, and unambiguously measurable prediction that is observationally distinguishable from competing alternatives, to be testable?
How would you test it? What are the observable differences from the usual evolutioniary scenario? This thing needs a whole lot of work before it rises to the level of âtestableâ.
Has he? Shouldnât it make an explicitly, concrete, and unambiguously measurable prediction that is observationally distinguishable from competing alternatives, to be testable?
It needs a little help. I think @Royâs suggestion #227 is one way to approach it - and (I predict) also quickly rejected by phylogenetic models comparing it to Common Descent.
My point here is that Gil has gone out on a limb to pose a hypothesis that (with a little help) could be testable. This is not any great development in evolutionary biology, but itâs a huge step for a Creationist. I do not intend faint praise - imagine if every Creationist could do the same.
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Only if @giltil actually adopts that pattern as a prediction of his hypothesis, which I predict he will not.
@Giltil You wonât get a better straight line than this. 