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“Anyway, no one really knows how to define a species, and there is controversy about any proof that one species has ever become another species. The concept of Ring Species is sometimes mentioned as pretty good proof. But Ring Species seem to provide evidence of salamanders turning into … salamanders. And seagulls turning into … seagulls. Not everyone is impressed by this. “

—One could argue that Australopithecines turning into Homo sapiens is just apes turning into apes, and so isn’t really evolution at all.

“Now, what’s higher than a Species? Well, in ascending order you get Genus, Family, Order, Class. Now we’re at a pretty high level. An example of a Class would be “mammal” or “fish”. No one in their right mind imagines that a fish would – POOF! – turn into a mammal. That would be crazy, right?
What’s above Class? Well, at an even higher level you have a Plylum. An example would be Vertebrates or mollusks. A scallop turning into a mammal? I don’t think so. Hey, wanna know what’s really interesting about the Cambrian Explosion?? That’s when almost all the Phyla suddenly appeared. Basically, 600 million years ago, Phyla just started popping into existence. It’s not clear that there was much of anything as an intermediate step. One day you have mollusks, then the next day you have vertebrates. Wild, huh? I don’t think a nifty invention like sperm will help a mollusk suddenly evolve into a whole new Phyla – like a vertebrate — but who knows?
Now, remember, we have a hard time really explaining lions and a tigers and speciation and how they might have evolved within the Felis genus. No really good explanation for that – just a Theory. We call them species but we don’t really know what we mean when we say that. But, 600 Million Years Ago (so they say) much more magic things were happening – POOF!”

—I get the impression that you believe that the start of a new phyla requires a larger ‘jump’ than the start of a new species. Actually, it’s no different. In fact, it’s not really possible to know if one is witnessing the start of what will become a new phyla.
Phylum require what is sometimes known as a “retrospective coronation”. That is, a group of somethings can only become classified into a new phyla long after the time that the phyla is said to have started.

Essentially, by definition, a phyla is not something that can form very recently - or that could form tomorrow. It’s a label that would we put on a group of life forms only after many speciation events. An analogy to a phylum and how it forms might be like the start of a new language – or better yet a language family (such as the “Romance Languages” of Latin, French, Romanian, etc). The witnesses to the time of the beginning of Latin probably wouldn’t have seen it as the beginning of a new language, but instead as merely a variation of another language (probably Greek?). And even if someone did see it as the beginning of a new language (which is highly unlikely) they certainly wouldn’t have seen it as the beginning of a whole new family type of languages. And thus the beginning of a language family is also something that, essentially by definition, is something that could only have occurred long ago. It won’t happen today. And the time that we call the beginning of a language will always be a case of “retrospective coronation”. Anyone living at the time of the beginning of Latin would have looked at that start as just a population of people speaking barely any differently than other population - we can look back and call that time the beginning of a new language (and new language family) only because of our position far in the future and knowing what occurred later.

Likewise, no sane taxonomist living at the time of the ‘Cambrian Explosion’ would separate many of the lifeforms he sees into separate phyla as we do today. There wasn’t much differentiation between most of the ‘phlya’ at that point. Many of what we regard as separate phyla from that period are just slightly different wormy things that are close cousins of each other. Look at many of the lifeforms at that point and notice that, even when there’s excellent preservation, it’s often debated as to which phyla to put it in – this is because many of the phyla were so alike. For instance, what are thought to be early chordates at this time – Pikaia, Yunnanozoon, and Haikouella – in each case it’s debated as to whether they are chordates or some other phyla. And, as mentioned, in most cases the only reason for feeling the need of placing many of the lifeforms into separate ‘phyla’ is because of retrospective coronation.

Also, the Cambrian ‘Explosion’ wasn’t as impressive as once thought – the ‘explosion’ has been fizzling for the past century. It used to be thought of as the beginning of life, but it was found that that isn’t true. Then it was thought to be the beginning of multicellular life, but that isn’t true either. Then it was thought to be at least the start of animal life, but that isn’t true. Today, I often see it claimed, from many biologists, that the Cambrian Explosion was the start of “most animal phyla”. Looking at the actual data though, even that may turn out to be a gross exaggeration.

From E. O. Wilson’s “The Diversity of Life”: “The number of living animal phyla … is about thirty-three. Of these, approximately twenty comprise animals large and abundant enough to leave fossils of the kind preserved in beds of the Burgess Shale type. The number of Cambrian phyla identified with confidence remains at eleven.”

That was in 2001. Doing a bit of research to see what the latest numbers are, it looks like there are now 36 animal phyla (due to some reclassifying – notice that defining ‘phyla’ is problematic as well), and of these about 17 are thought to be identified from the Cambrian fossil record (so less than half). And of these 17, most existed prior to the Cambrian Explosion (Porifera, Mollusca, Annelida, Cnidaria, and Arthropoda, and probably Chordata, Nematode, Echinodermata, Brachiopods, and Placozoa). Most of the rest make their appearance well after the Cambrian (e.g. Rotifers, Onychophora, Nematomorpha, Echiura, Annelida).

So of the 36 or so phyla, perhaps 7-10 originated during the Cambrian Explosion (and that number could shrink as the fossil record of the pre-Cambrian continues to improve). More phyla appeared both before, and after the CE, than what appeared during the CE itself. So after the CE we have little wormy things, but no amphibians, no reptiles, no mammals, no insects (which make up 3/4 of all species), no birds, no dinos, no trees or flowering plants, etc etc. All of these have formed since then. That’s a bit more than a “tweaking” as you put it earlier.